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<span class="vector-toc-numb">6</span> <span>Implementations</span> </div> </a> <button aria-controls="toc-Implementations-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Implementations subsection</span> </button> <ul id="toc-Implementations-sublist" class="vector-toc-list"> <li id="toc-Heap-based" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Heap-based"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.1</span> <span>Heap-based</span> </div> </a> <ul id="toc-Heap-based-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-dlmalloc_and_ptmalloc" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#dlmalloc_and_ptmalloc"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.2</span> <span>dlmalloc and ptmalloc</span> </div> </a> <ul id="toc-dlmalloc_and_ptmalloc-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-FreeBSD's_and_NetBSD's_jemalloc" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#FreeBSD's_and_NetBSD's_jemalloc"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.3</span> <span>FreeBSD's and NetBSD's jemalloc</span> </div> </a> <ul id="toc-FreeBSD's_and_NetBSD's_jemalloc-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-OpenBSD's_malloc" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#OpenBSD's_malloc"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.4</span> <span>OpenBSD's malloc</span> </div> </a> <ul id="toc-OpenBSD's_malloc-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Hoard_malloc" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Hoard_malloc"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.5</span> <span>Hoard malloc</span> </div> </a> <ul id="toc-Hoard_malloc-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-mimalloc" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#mimalloc"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.6</span> <span>mimalloc</span> </div> </a> <ul id="toc-mimalloc-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Thread-caching_malloc_(tcmalloc)" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Thread-caching_malloc_(tcmalloc)"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.7</span> <span>Thread-caching malloc (tcmalloc)</span> </div> </a> <ul id="toc-Thread-caching_malloc_(tcmalloc)-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-In-kernel" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#In-kernel"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.8</span> <span>In-kernel</span> </div> </a> <ul id="toc-In-kernel-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Overriding_malloc" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Overriding_malloc"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Overriding malloc</span> </div> </a> <ul id="toc-Overriding_malloc-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Allocation_size_limits" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Allocation_size_limits"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>Allocation size limits</span> </div> </a> <ul id="toc-Allocation_size_limits-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Extensions_and_alternatives" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Extensions_and_alternatives"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>Extensions and alternatives</span> </div> </a> <ul id="toc-Extensions_and_alternatives-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">10</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">11</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div 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class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Dynamick%C3%A1_alokace_pam%C4%9Bti_v_jazyce_C" title="Dynamická alokace paměti v jazyce C – Czech" lang="cs" hreflang="cs" data-title="Dynamická alokace paměti v jazyce C" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%A7%D8%AE%D8%AA%D8%B5%D8%A7%D8%B5_%D8%AD%D8%A7%D9%81%D8%B8%D9%87_%D9%BE%D9%88%DB%8C%D8%A7_%D8%AF%D8%B1_%D8%B3%DB%8C" title="اختصاص حافظه پویا در سی – Persian" lang="fa" hreflang="fa" data-title="اختصاص حافظه پویا در سی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/C_%EB%8F%99%EC%A0%81_%EB%A9%94%EB%AA%A8%EB%A6%AC_%ED%95%A0%EB%8B%B9" title="C 동적 메모리 할당 – Korean" lang="ko" hreflang="ko" data-title="C 동적 메모리 할당" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Aloca%C3%A7%C3%A3o_din%C3%A2mica_de_mem%C3%B3ria_em_C" title="Alocação dinâmica de memória em C – Portuguese" lang="pt" hreflang="pt" data-title="Alocação dinâmica de memória em C" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/C_dynamic_memory_allocation" title="C dynamic memory allocation – Simple English" lang="en-simple" hreflang="en-simple" data-title="C dynamic memory allocation" 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functions">Mathematics</a></li> <li><a href="/wiki/C_file_input/output" title="C file input/output">File input/output</a></li> <li><a href="/wiki/C_date_and_time_functions" title="C date and time functions">Date/time</a></li> <li><a href="/wiki/C_localization_functions" title="C localization functions">Localization</a></li> <li><a class="mw-selflink selflink">Memory allocation</a></li> <li><a href="/wiki/C_process_control" title="C process control">Process control</a></li> <li><a href="/wiki/C_signal_handling" title="C signal handling">Signals</a></li> <li><a href="/wiki/C_alternative_tokens" title="C alternative tokens">Alternative tokens</a></li></ul></td> </tr><tr><th class="sidebar-heading"> Miscellaneous headers</th></tr><tr><td class="sidebar-content"> <ul><li><span class="monospaced"><<a href="/wiki/Assert.h" title="Assert.h">assert.h</a>></span></li> <li><span class="monospaced"><<a href="/wiki/Errno.h" title="Errno.h">errno.h</a>></span></li> <li><span class="monospaced"><<a href="/wiki/Setjmp.h" title="Setjmp.h">setjmp.h</a>></span></li> <li><span class="monospaced"><<a href="/wiki/Stdarg.h" title="Stdarg.h">stdarg.h</a>></span></li></ul></td> </tr><tr><td class="sidebar-navbar"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:C_standard_library" title="Template:C standard library"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:C_standard_library" title="Template talk:C standard library"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:C_standard_library" title="Special:EditPage/Template:C standard library"><abbr title="Edit this template">e</abbr></a></li></ul></div></td></tr></tbody></table> <p><b>C dynamic memory allocation</b> refers to performing <a href="/wiki/Manual_memory_management" title="Manual memory management">manual memory management</a> for <a href="/wiki/Dynamic_memory_allocation" class="mw-redirect" title="Dynamic memory allocation">dynamic memory allocation</a> in the <a href="/wiki/C_(programming_language)" title="C (programming language)">C programming language</a> via a group of functions in the <a href="/wiki/C_standard_library" title="C standard library">C standard library</a>, namely <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734"><span class="monospaced">malloc</span>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734"><span class="monospaced">realloc</span>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734"><span class="monospaced">calloc</span>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734"><span class="monospaced">aligned_alloc</span> and <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734"><span class="monospaced">free</span>.<sup id="cite_ref-c99_1-0" class="reference"><a href="#cite_note-c99-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p><p>The <a href="/wiki/C%2B%2B" title="C++">C++</a> programming language includes these functions; however, the operators <a href="/wiki/New_and_delete_(C%2B%2B)" title="New and delete (C++)"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734"><span class="monospaced">new</span> and <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734"><span class="monospaced">delete</span></a> provide similar functionality and are recommended by that language's authors.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Still, there are several situations in which using <code>new</code>/<code>delete</code> is not applicable, such as garbage collection code or performance-sensitive code, and a combination of <code>malloc</code> and placement <code>new</code> may be required instead of the higher-level <code>new</code> operator. </p><p>Many different implementations of the actual memory allocation mechanism, used by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734"><span class="monospaced">malloc</span>, are available. Their performance varies in both execution time and required memory. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Rationale">Rationale</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=1" title="Edit section: Rationale"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/C_(programming_language)" title="C (programming language)">C programming language</a> manages memory <a href="/wiki/Static_memory_allocation" class="mw-redirect" title="Static memory allocation">statically</a>, <a href="/wiki/Automatic_memory_allocation" class="mw-redirect" title="Automatic memory allocation">automatically</a>, or <a href="/wiki/Dynamic_memory_allocation" class="mw-redirect" title="Dynamic memory allocation">dynamically</a>. Static-duration variables are allocated in main memory, usually along with the executable code of the program, and persist for the lifetime of the program; automatic-duration variables are allocated on the <a href="/wiki/Call_stack" title="Call stack">stack</a> and come and go as functions are called and return. For static-duration and automatic-duration variables, the size of the allocation must be <a href="/wiki/Compile-time" class="mw-redirect" title="Compile-time">compile-time</a> constant (except for the case of variable-length automatic arrays<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>). If the required size is not known until <a href="/wiki/Run_time_(program_lifecycle_phase)" class="mw-redirect" title="Run time (program lifecycle phase)">run-time</a> (for example, if data of arbitrary size is being read from the user or from a disk file), then using fixed-size data objects is inadequate. </p><p>The lifetime of allocated memory can also cause concern. Neither static- nor automatic-duration memory is adequate for all situations. Automatic-allocated data cannot persist across multiple function calls, while static data persists for the life of the program whether it is needed or not. In many situations the programmer requires greater flexibility in managing the lifetime of allocated memory. </p><p>These limitations are avoided by using <a href="/wiki/Dynamic_memory_allocation" class="mw-redirect" title="Dynamic memory allocation">dynamic memory allocation</a>, in which memory is more explicitly (but more flexibly) managed, typically by allocating it from the <span class="citation-needed-content" style="padding-left:0.1em; padding-right:0.1em; color:var(--color-subtle, #54595d); border:1px solid var(--border-color-subtle, #c8ccd1);"><i>free store</i> (informally called the "heap"),</span><sup class="noprint Inline-Template Template-Fact" style="margin-left:0.1em; white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="In my experience 'heap' is almost exclusively used in a C context. While free store is used in C++ context for the new/delete operators. (July 2022)">citation needed</span></a></i>]</sup> an area of memory structured for this purpose. In C, the library function <code>malloc</code> is used to allocate a block of memory on the heap. The program accesses this block of memory via a <a href="/wiki/Pointer_(computer_programming)" title="Pointer (computer programming)">pointer</a> that <code>malloc</code> returns. When the memory is no longer needed, the pointer is passed to <code>free</code> which deallocates the memory so that it can be used for other purposes. </p><p>The original description of C indicated that <code>calloc</code> and <code>cfree</code> were in the standard library, but not <code>malloc</code>. Code for a simple model implementation of a storage manager for <a href="/wiki/Unix" title="Unix">Unix</a> was given with <code>alloc</code> and <code>free</code> as the user interface functions, and using the <code><a href="/wiki/Sbrk" title="Sbrk">sbrk</a></code> system call to request memory from the operating system.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> The 6th Edition Unix documentation gives <code>alloc</code> and <code>free</code> as the low-level memory allocation functions.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> The <code>malloc</code> and <code>free</code> routines in their modern form are completely described in the 7th Edition Unix manual.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> </p><p>Some platforms provide library or <a href="/wiki/Intrinsic_function" title="Intrinsic function">intrinsic function</a> calls which allow run-time dynamic allocation from the C stack rather than the heap (e.g. <code>alloca()</code><sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup>). This memory is automatically freed when the calling function ends. </p> <div class="mw-heading mw-heading2"><h2 id="Overview_of_functions">Overview of functions</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=2" title="Edit section: Overview of functions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The C dynamic memory allocation functions are defined in <code>stdlib.h</code> header (<code>cstdlib</code> header in C++).<sup id="cite_ref-c99_1-1" class="reference"><a href="#cite_note-c99-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable"> <tbody><tr> <th>Function </th> <th>Description </th></tr> <tr> <td><span class="anchor" id="malloc"></span><code class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><span class="n">malloc</span></code> </td> <td>allocates the specified number of bytes </td></tr> <tr> <td><span class="anchor" id="aligned_alloc"></span><code class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><span class="n">aligned_alloc</span></code> </td> <td>allocates the specified number of bytes at the specified alignment </td></tr> <tr> <td><span class="anchor" id="realloc"></span><code class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><span class="n">realloc</span></code> </td> <td>increases or decreases the size of the specified block of memory, moving it if necessary </td></tr> <tr> <td><span class="anchor" id="calloc"></span><code class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><span class="n">calloc</span></code> </td> <td>allocates the specified number of bytes and initializes them to zero </td></tr> <tr> <td><span class="anchor" id="free"></span><code class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><span class="n">free</span></code> </td> <td>releases the specified block of memory back to the system </td></tr></tbody></table> <div class="mw-heading mw-heading3"><h3 id="Differences_between_malloc()_and_calloc()"><span id="Differences_between_malloc.28.29_and_calloc.28.29"></span>Differences between <code>malloc()</code> and <code>calloc()</code></h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=3" title="Edit section: Differences between malloc() and calloc()"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><code>malloc()</code> takes a single argument (the amount of memory to allocate in bytes), while <code>calloc()</code> takes two arguments — the number of elements and the size of each element.</li> <li><code>malloc()</code> only allocates memory, while <code>calloc()</code> allocates and sets the bytes in the allocated region to zero.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup></li></ul> <div class="mw-heading mw-heading2"><h2 id="Usage_example">Usage example</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=4" title="Edit section: Usage example"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Creating an <a href="/wiki/Array_data_structure" class="mw-redirect" title="Array data structure">array</a> of ten integers with automatic scope is straightforward in C: </p> <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="n">array</span><span class="p">[</span><span class="mi">10</span><span class="p">];</span> </pre></div> <p>However, the size of the array is fixed at compile time. If one wishes to allocate a similar array dynamically without using a <a href="/wiki/Variable-length_array" title="Variable-length array">variable-length array</a>, which is not guaranteed to be supported in all <a href="/wiki/C11_(C_standard_revision)" title="C11 (C standard revision)">C11</a> implementations, the following code can be used: </p> <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">array</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">malloc</span><span class="p">(</span><span class="mi">10</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span> </pre></div> <p>This computes the number of bytes that ten integers occupy in memory, then requests that many bytes from <code>malloc</code> and assigns the result to a <a href="/wiki/Pointer_(computer_programming)" title="Pointer (computer programming)">pointer</a> named <code>array</code> (due to C syntax, pointers and arrays can be used interchangeably in some situations). </p><p>Because <code>malloc</code> might not be able to service the request, it might return a <a href="/wiki/Null_pointer" title="Null pointer">null pointer</a> and it is <a href="/wiki/Coding_best_practices" title="Coding best practices">good programming practice</a> to check for this: </p> <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">array</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">malloc</span><span class="p">(</span><span class="mi">10</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span> <span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">array</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nb">NULL</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> <span class="w"> </span><span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">"malloc failed</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">-1</span><span class="p">;</span> <span class="p">}</span> </pre></div> <p>When the program no longer needs the <a href="/wiki/Dynamic_array" title="Dynamic array">dynamic array</a>, it must eventually call <code>free</code> to return the memory it occupies to the free store: </p> <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre><span></span><span class="n">free</span><span class="p">(</span><span class="n">array</span><span class="p">);</span> </pre></div> <p>The memory set aside by <code>malloc</code> is not <a href="/wiki/Initialization_(programming)" title="Initialization (programming)">initialized</a> and may contain <a href="/wiki/Cruft" title="Cruft">cruft</a>: the remnants of previously used and discarded data. After allocation with <code>malloc</code>, elements of the array are <a href="/wiki/Uninitialized_variable" title="Uninitialized variable">uninitialized variables</a>. The command <code>calloc</code> will return an allocation that has already been cleared: </p> <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">array</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">calloc</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span> </pre></div> <p>With realloc we can resize the amount of memory a pointer points to. For example, if we have a pointer acting as an array of size <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle n}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>n</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle n}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a601995d55609f2d9f5e233e36fbe9ea26011b3b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.395ex; height:1.676ex;" alt="{\displaystyle n}"></span> and we want to change it to an array of size <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle m}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>m</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle m}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/0a07d98bb302f3856cbabc47b2b9016692e3f7bc" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:2.04ex; height:1.676ex;" alt="{\displaystyle m}"></span>, we can use realloc. </p> <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">arr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">malloc</span><span class="p">(</span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span> <span class="n">arr</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span> <span class="n">arr</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span> <span class="n">arr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">realloc</span><span class="p">(</span><span class="n">arr</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="kt">int</span><span class="p">));</span> <span class="n">arr</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span> </pre></div> <p>Note that realloc must be assumed to have changed the base address of the block (i.e. if it has failed to extend the size of the original block, and has therefore allocated a new larger block elsewhere and copied the old contents into it). Therefore, any pointers to addresses within the original block are also no longer valid. </p> <div class="mw-heading mw-heading2"><h2 id="Type_safety">Type safety</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=5" title="Edit section: Type safety"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><code>malloc</code> returns a <a href="/wiki/Void_pointer" class="mw-redirect" title="Void pointer">void pointer</a> (<code>void *</code>), which indicates that it is a pointer to a region of unknown data type. The use of casting is required in C++ due to the strong type system, whereas this is not the case in C. One may "cast" (see <a href="/wiki/Type_conversion" title="Type conversion">type conversion</a>) this pointer to a specific type: </p> <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="p">,</span><span class="w"> </span><span class="o">*</span><span class="n">ptr2</span><span class="p">;</span> <span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">malloc</span><span class="p">(</span><span class="mi">10</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="o">*</span><span class="n">ptr</span><span class="p">));</span><span class="w"> </span><span class="cm">/* without a cast */</span> <span class="n">ptr2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="p">)</span><span class="n">malloc</span><span class="p">(</span><span class="mi">10</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="o">*</span><span class="n">ptr</span><span class="p">));</span><span class="w"> </span><span class="cm">/* with a cast */</span> </pre></div> <p>There are advantages and disadvantages to performing such a cast. </p> <div class="mw-heading mw-heading3"><h3 id="Advantages_to_casting">Advantages to casting</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=6" title="Edit section: Advantages to casting"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li>Including the cast may allow a C program or function to compile as C++.</li> <li>The cast allows for <a href="/wiki/ANSI_C" title="ANSI C">pre-1989 versions</a> of <code>malloc</code> that originally returned a <code>char *</code>.<sup id="cite_ref-Cprog_malloc_12-0" class="reference"><a href="#cite_note-Cprog_malloc-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup></li> <li>Casting can help the developer identify inconsistencies in type sizing should the destination pointer type change, particularly if the pointer is declared far from the <code>malloc()</code> call (although modern compilers and static analysers can warn on such behaviour without requiring the cast<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup>).</li></ul> <div class="mw-heading mw-heading3"><h3 id="Disadvantages_to_casting">Disadvantages to casting</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=7" title="Edit section: Disadvantages to casting"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li>Under the C standard, the cast is redundant.</li> <li>Adding the cast may mask failure to include the header <code>stdlib.h</code>, in which the <a href="/wiki/Function_prototype" title="Function prototype">function prototype</a> for <code>malloc</code> is found.<sup id="cite_ref-Cprog_malloc_12-1" class="reference"><a href="#cite_note-Cprog_malloc-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> In the absence of a prototype for <code>malloc</code>, the C90 standard requires that the C compiler assume <code>malloc</code> returns an <code>int</code>. If there is no cast, C90 requires a diagnostic when this integer is assigned to the pointer; however, with the cast, this diagnostic would not be produced, hiding a bug. On certain architectures and data models (such as LP64 on 64-bit systems, where <code>long</code> and pointers are 64-bit and <code>int</code> is 32-bit), this error can actually result in undefined behaviour, as the implicitly declared <code>malloc</code> returns a 32-bit value whereas the actually defined function returns a 64-bit value. Depending on calling conventions and memory layout, this may result in <a href="/wiki/Stack_smashing" class="mw-redirect" title="Stack smashing">stack smashing</a>. This issue is less likely to go unnoticed in modern compilers, as C99 does not permit implicit declarations, so the compiler must produce a diagnostic even if it does assume <code>int</code> return.</li> <li>If the type of the pointer is changed at its declaration, one may also need to change all lines where <code>malloc</code> is called and cast.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Common_errors">Common errors</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=8" title="Edit section: Common errors"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The improper use of dynamic memory allocation can frequently be a source of bugs. These can include security bugs or program crashes, most often due to <a href="/wiki/Segmentation_fault" title="Segmentation fault">segmentation faults</a>. </p><p>Most common errors are as follows:<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> </p> <dl><dt>Not checking for allocation failures</dt> <dd>Memory allocation is not guaranteed to succeed, and may instead return a null pointer. Using the returned value, without checking if the allocation is successful, invokes <a href="/wiki/Undefined_behavior" title="Undefined behavior">undefined behavior</a>. This usually leads to crash (due to the resulting segmentation fault on the null pointer dereference), but there is no guarantee that a crash will happen so relying on that can also lead to problems.</dd> <dt>Memory leaks</dt> <dd>Failure to deallocate memory using <code>free</code> leads to buildup of non-reusable memory, which is no longer used by the program. This wastes memory resources and can lead to allocation failures when these resources are exhausted. <span class="anchor" id="Use_after_free"></span></dd> <dt>Logical errors</dt> <dd>All allocations must follow the same pattern: allocation using <code>malloc</code>, usage to store data, deallocation using <code>free</code>. Failures to adhere to this pattern, such as memory usage after a call to <code>free</code> (<a href="/wiki/Dangling_pointer" title="Dangling pointer">dangling pointer</a>) or before a call to <code>malloc</code> (<a href="/wiki/Wild_pointer" class="mw-redirect" title="Wild pointer">wild pointer</a>), calling <code>free</code> twice ("double free"), etc., usually causes a segmentation fault and results in a crash of the program. These errors can be transient and hard to debug – for example, freed memory is usually not immediately reclaimed by the OS, and thus dangling pointers may persist for a while and appear to work.</dd></dl> <p>In addition, as an interface that precedes ANSI C standardization, <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">malloc</code> and its associated functions have behaviors that were intentionally left to the implementation to define for themselves. One of them is the zero-length allocation, which is more of a problem with <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">realloc</code> since it is more common to resize to zero.<sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> Although both <a href="/wiki/POSIX" title="POSIX">POSIX</a> and the <a href="/wiki/Single_Unix_Specification" class="mw-redirect" title="Single Unix Specification">Single Unix Specification</a> require proper handling of 0-size allocations by either returning <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">NULL</code> or something else that can be safely freed,<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> not all platforms are required to abide by these rules. Among the many double-free errors that it has led to, the 2019 <a href="/wiki/WhatsApp" title="WhatsApp">WhatsApp</a> RCE was especially prominent.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> A way to wrap these functions to make them safer is by simply checking for 0-size allocations and turning them into those of size 1. (Returning <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">NULL</code> has its own problems: it otherwise indicates an out-of-memory failure. In the case of <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">realloc</code> it would have signaled that the original memory was not moved and freed, which again is not the case for size 0, leading to the double-free.)<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Implementations">Implementations</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=9" title="Edit section: Implementations"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The implementation of memory management depends greatly upon operating system and architecture. Some operating systems supply an allocator for malloc, while others supply functions to control certain regions of data. The same dynamic memory allocator is often used to implement both <code>malloc</code> and the operator <code>new</code> in <a href="/wiki/C%2B%2B" title="C++">C++</a>.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Heap-based">Heap-based</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=10" title="Edit section: Heap-based"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Sbrk" title="Sbrk">sbrk</a></div> <p>Implementation of legacy allocators was commonly done using the <a href="/wiki/Data_segment#Heap" title="Data segment">heap segment</a>. The allocator would usually expand and contract the heap to fulfill allocation requests. </p><p>The heap method suffers from a few inherent flaws: </p> <ul><li>A linear allocator can only shrink if the last allocation is released. Even if largely unused, the heap can get "stuck" at a very large size because of a small but long-lived allocation at its tip which could waste any amount of address space, although some allocators on some systems may be able to release entirely empty intermediate pages to the OS.</li> <li>A linear allocator is sensitive to <a href="/wiki/Fragmentation_(computer)" class="mw-redirect" title="Fragmentation (computer)">fragmentation</a>. A good allocator will attempt to track and reuse free slots through the entire heap, but as allocation sizes and lifetimes get mixed it can be difficult and expensive to find or coalesce free segments large enough to hold new allocation requests.</li> <li>A linear allocator has extremely poor concurrency characteristics, as the heap segment is per-process every thread has to synchronise on allocation, and concurrent allocations from threads which may have very different work loads amplifies the previous two issues.</li></ul> <p><span class="anchor" id="dlmalloc"></span> </p> <div class="mw-heading mw-heading3"><h3 id="dlmalloc_and_ptmalloc">dlmalloc and ptmalloc<span class="anchor" id="dlmalloc"></span></h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=11" title="Edit section: dlmalloc and ptmalloc"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Doug_Lea" title="Doug Lea">Doug Lea</a> has developed the <a href="/wiki/Public_domain" title="Public domain">public domain</a> dlmalloc ("Doug Lea's Malloc") as a general-purpose allocator, starting in 1987. The <a href="/wiki/GNU_C_library" class="mw-redirect" title="GNU C library">GNU C library</a> (glibc) is derived from Wolfram Gloger's ptmalloc ("pthreads malloc"), a fork of dlmalloc with threading-related improvements.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-phrack-57-8_22-0" class="reference"><a href="#cite_note-phrack-57-8-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> As of November 2023, the latest version of dlmalloc is version 2.8.6 from August 2012.<sup id="cite_ref-dlmalloc_24-0" class="reference"><a href="#cite_note-dlmalloc-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> </p><p>dlmalloc is a boundary tag allocator. Memory on the <a href="/wiki/Heap_memory" class="mw-redirect" title="Heap memory">heap</a> is allocated as "chunks", an 8-byte <a href="/wiki/Data_structure_alignment" title="Data structure alignment">aligned</a> <a href="/wiki/Data_structure" title="Data structure">data structure</a> which contains a header, and usable memory. Allocated memory contains an 8- or 16-byte overhead for the size of the chunk and usage flags (similar to a <a href="/wiki/Dope_vector" title="Dope vector">dope vector</a>). Unallocated chunks also store pointers to other free chunks in the usable space area, making the minimum chunk size 16 bytes on 32-bit systems and 24/32 (depends on alignment) bytes on 64-bit systems.<sup id="cite_ref-phrack-57-8_22-1" class="reference"><a href="#cite_note-phrack-57-8-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-dlmalloc_24-1" class="reference"><a href="#cite_note-dlmalloc-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Location: 2.8.6, Minimum allocated size">: 2.8.6, Minimum allocated size </span></sup> </p><p>Unallocated memory is grouped into "<a href="/wiki/Bin_(computational_geometry)" title="Bin (computational geometry)">bins</a>" of similar sizes, implemented by using a double-linked list of chunks (with pointers stored in the unallocated space inside the chunk). Bins are sorted by size into three classes:<sup id="cite_ref-phrack-57-8_22-2" class="reference"><a href="#cite_note-phrack-57-8-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-dlmalloc_24-2" class="reference"><a href="#cite_note-dlmalloc-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Location: Overlaid data structures">: Overlaid data structures </span></sup> </p> <ul><li>For requests below 256 bytes (a "smallbin" request), a simple two power best fit allocator is used. If there are no free blocks in that bin, a block from the next highest bin is split in two.</li> <li>For requests of 256 bytes or above but below the <a href="/wiki/Mmap" title="Mmap">mmap</a> threshold, dlmalloc since v2.8.0 use <a href="/wiki/Trie#Bitwise_tries" title="Trie">an in-place <i>bitwise trie</i> algorithm</a> ("treebin"). If there is no free space left to satisfy the request, dlmalloc tries to increase the size of the heap, usually via the <a href="/wiki/Sbrk" title="Sbrk">brk</a> system call. This feature was introduced way after ptmalloc was created (from v2.7.x), and as a result is not a part of glibc, which inherits the old best-fit allocator.</li> <li>For requests above the mmap threshold (a "largebin" request), the memory is always allocated using the <a href="/wiki/Mmap" title="Mmap">mmap</a> system call. The threshold is usually 128 KB.<sup id="cite_ref-glibc-env_25-0" class="reference"><a href="#cite_note-glibc-env-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> The mmap method averts problems with huge buffers trapping a small allocation at the end after their expiration, but always allocates an entire <a href="/wiki/Page_(computer_memory)" title="Page (computer memory)">page</a> of memory, which on many architectures is 4096 bytes in size.<sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup></li></ul> <p>Game developer Adrian Stone argues that <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">dlmalloc</code>, as a boundary-tag allocator, is unfriendly for console systems that have virtual memory but do not have <a href="/wiki/Demand_paging" title="Demand paging">demand paging</a>. This is because its pool-shrinking and growing callbacks (<code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">sysmalloc</code>/<code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">systrim</code>) cannot be used to allocate and commit individual pages of virtual memory. In the absence of demand paging, fragmentation becomes a greater concern.<sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> </p><p><span class="anchor" id="jemalloc"></span> </p> <div class="mw-heading mw-heading3"><h3 id="FreeBSD's_and_NetBSD's_jemalloc"><span id="FreeBSD.27s_and_NetBSD.27s_jemalloc"></span>FreeBSD's and NetBSD's jemalloc</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=12" title="Edit section: FreeBSD's and NetBSD's jemalloc"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Since <a href="/wiki/FreeBSD" title="FreeBSD">FreeBSD</a> 7.0 and <a href="/wiki/NetBSD" title="NetBSD">NetBSD</a> 5.0, the old <code>malloc</code> implementation (<code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">phkmalloc</code> by <a href="/wiki/Poul-Henning_Kamp" title="Poul-Henning Kamp">Poul-Henning Kamp</a>) was replaced by <a rel="nofollow" class="external text" href="http://jemalloc.net/">jemalloc</a>, written by Jason Evans. The main reason for this was a lack of scalability of <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">phkmalloc</code> in terms of multithreading. In order to avoid lock contention, <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">jemalloc</code> uses separate "arenas" for each <a href="/wiki/Central_processing_unit" title="Central processing unit">CPU</a>. Experiments measuring number of allocations per second in multithreading application have shown that this makes it scale linearly with the number of threads, while for both phkmalloc and dlmalloc performance was inversely proportional to the number of threads.<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> </p><p><span class="anchor" id="openbsd"></span> </p> <div class="mw-heading mw-heading3"><h3 id="OpenBSD's_malloc"><span id="OpenBSD.27s_malloc"></span>OpenBSD's malloc</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=13" title="Edit section: OpenBSD's malloc"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/OpenBSD" title="OpenBSD">OpenBSD</a>'s implementation of the <code>malloc</code> function makes use of <a href="/wiki/Mmap" title="Mmap">mmap</a>. For requests greater in size than one page, the entire allocation is retrieved using <code>mmap</code>; smaller sizes are assigned from memory pools maintained by <code>malloc</code> within a number of "bucket pages", also allocated with <code>mmap</code>.<sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup><sup class="noprint Inline-Template noprint noexcerpt Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:NOTRS" class="mw-redirect" title="Wikipedia:NOTRS"><span title="This claim needs references to better sources. (November 2015)">better source needed</span></a></i>]</sup> On a call to <code>free</code>, memory is released and unmapped from the process <a href="/wiki/Address_space" title="Address space">address space</a> using <code>munmap</code>. This system is designed to improve security by taking advantage of the <a href="/wiki/Address_space_layout_randomization" title="Address space layout randomization">address space layout randomization</a> and gap page features implemented as part of OpenBSD's <code>mmap</code> <a href="/wiki/System_call" title="System call">system call</a>, and to detect use-after-free bugs—as a large memory allocation is completely unmapped after it is freed, further use causes a <a href="/wiki/Segmentation_fault" title="Segmentation fault">segmentation fault</a> and termination of the program. </p><p>The GrapheneOS project initially started out by porting OpenBSD's memory allocator to Android's Bionic C Library.<sup id="cite_ref-30" class="reference"><a href="#cite_note-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> </p><p><span class="anchor" id="hoard"></span> </p> <div class="mw-heading mw-heading3"><h3 id="Hoard_malloc">Hoard malloc</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=14" title="Edit section: Hoard malloc"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Hoard_memory_allocator" title="Hoard memory allocator">Hoard memory allocator</a></div> <p>Hoard is an allocator whose goal is scalable memory allocation performance. Like OpenBSD's allocator, Hoard uses <code>mmap</code> exclusively, but manages memory in chunks of 64 kilobytes called superblocks. Hoard's heap is logically divided into a single global heap and a number of per-processor heaps. In addition, there is a thread-local cache that can hold a limited number of superblocks. By allocating only from superblocks on the local per-thread or per-processor heap, and moving mostly-empty superblocks to the global heap so they can be reused by other processors, Hoard keeps fragmentation low while achieving near linear scalability with the number of threads.<sup id="cite_ref-31" class="reference"><a href="#cite_note-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="mimalloc">mimalloc</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=15" title="Edit section: mimalloc"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Mimalloc" title="Mimalloc">mimalloc</a></div> <p>An <a href="/wiki/Open_source" title="Open source">open-source</a> compact general-purpose <a href="/wiki/Memory_allocator" class="mw-redirect" title="Memory allocator">memory allocator</a> from <a href="/wiki/Microsoft_Research" title="Microsoft Research">Microsoft Research</a> with focus on performance.<sup id="cite_ref-32" class="reference"><a href="#cite_note-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> The library is about 11,000 <a href="/wiki/Lines_of_code" class="mw-redirect" title="Lines of code">lines of code</a>. </p><p><span class="anchor" id="tcmalloc"></span> </p> <div class="mw-heading mw-heading3"><h3 id="Thread-caching_malloc_(tcmalloc)"><span id="Thread-caching_malloc_.28tcmalloc.29"></span>Thread-caching malloc (tcmalloc)</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=16" title="Edit section: Thread-caching malloc (tcmalloc)"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Every thread has a <a href="/wiki/Thread-local_storage" title="Thread-local storage">thread-local storage</a> for small allocations. For large allocations mmap or <a href="/wiki/Sbrk" title="Sbrk">sbrk</a> can be used. <a rel="nofollow" class="external text" href="https://code.google.com/p/gperftools/">TCMalloc</a>, a <i>malloc</i> developed by Google,<sup id="cite_ref-33" class="reference"><a href="#cite_note-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> has garbage-collection for local storage of dead threads. The TCMalloc is considered to be more than twice as fast as glibc's ptmalloc for multithreaded programs.<sup id="cite_ref-34" class="reference"><a href="#cite_note-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-35" class="reference"><a href="#cite_note-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="In-kernel">In-kernel</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=17" title="Edit section: In-kernel"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Operating system <a href="/wiki/Kernel_(operating_system)" title="Kernel (operating system)">kernels</a> need to allocate memory just as application programs do. The implementation of <code>malloc</code> within a kernel often differs significantly from the implementations used by C libraries, however. For example, memory buffers might need to conform to special restrictions imposed by <a href="/wiki/Direct_memory_access" title="Direct memory access">DMA</a>, or the memory allocation function might be called from interrupt context.<sup id="cite_ref-36" class="reference"><a href="#cite_note-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> This necessitates a <code>malloc</code> implementation tightly integrated with the <a href="/wiki/Virtual_memory" title="Virtual memory">virtual memory</a> subsystem of the operating system kernel. </p> <div class="mw-heading mw-heading2"><h2 id="Overriding_malloc">Overriding malloc</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=18" title="Edit section: Overriding malloc"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Because <code>malloc</code> and its relatives can have a strong impact on the performance of a program, it is not uncommon to override the functions for a specific application by custom implementations that are optimized for application's allocation patterns. The C standard provides no way of doing this, but operating systems have found various ways to do this by exploiting dynamic linking. One way is to simply link in a different library to override the symbols. Another, employed by <a href="/wiki/UNIX_System_V#SVR3" title="UNIX System V">Unix System V.3</a>, is to make <code>malloc</code> and <code>free</code> function pointers that an application can reset to custom functions.<sup id="cite_ref-Levine_1999_CH9_37-0" class="reference"><a href="#cite_note-Levine_1999_CH9-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> </p><p>The most common form on POSIX-like systems is to set the environment variable LD_PRELOAD with the path of the allocator, so that the dynamic linker uses that version of malloc/calloc/free instead of the libc implementation. </p> <div class="mw-heading mw-heading2"><h2 id="Allocation_size_limits">Allocation size limits</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=19" title="Edit section: Allocation size limits"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The largest possible memory block <code>malloc</code> can allocate depends on the host system, particularly the size of physical memory and the operating system implementation. </p><p>Theoretically, the largest number should be the maximum value that can be held in a <code><a href="/wiki/Size_t" class="mw-redirect" title="Size t">size_t</a></code> type, which is an implementation-dependent unsigned integer representing the size of an area of memory. In the <a href="/wiki/C99" title="C99">C99</a> standard and later, it is available as the <code>SIZE_MAX</code> constant from <code><<a href="/wiki/Stdint.h" class="mw-redirect" title="Stdint.h">stdint.h</a>></code>. Although not guaranteed by <span class="nowrap">ISO C</span>, it is usually <code>2^(CHAR_BIT * <a href="/wiki/Sizeof" title="Sizeof">sizeof</a>(size_t)) - 1</code>. </p><p>On glibc systems, the largest possible memory block <code>malloc</code> can allocate is only half this size, namely <code>2^(CHAR_BIT * <a href="/wiki/Sizeof" title="Sizeof">sizeof</a>(ptrdiff_t) - 1) - 1</code>.<sup id="cite_ref-38" class="reference"><a href="#cite_note-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Extensions_and_alternatives">Extensions and alternatives</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=20" title="Edit section: Extensions and alternatives"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The C library implementations shipping with various operating systems and compilers may come with alternatives and extensions to the standard <code>malloc</code> interface. Notable among these is: </p> <ul><li><code><a href="/wiki/Alloca" class="mw-redirect" title="Alloca">alloca</a></code>, which allocates a requested number of bytes on the <a href="/wiki/Call_stack" title="Call stack">call stack</a>. No corresponding deallocation function exists, as typically the memory is deallocated as soon as the calling function returns. <code>alloca</code> was present on Unix systems as early as <a href="/wiki/UNIX/32V" title="UNIX/32V">32/V</a> (1978), but its use can be problematic in some (e.g., embedded) contexts.<sup id="cite_ref-39" class="reference"><a href="#cite_note-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> While supported by many compilers, it is not part of the <a href="/wiki/ANSI_C" title="ANSI C">ANSI-C</a> standard and therefore may not always be portable. It may also cause minor performance problems: it leads to variable-size stack frames, so that both <a href="/wiki/Call_stack#STACK-POINTER" title="Call stack">stack and frame pointers</a> need to be managed (with fixed-size stack frames, one of these is redundant).<sup id="cite_ref-40" class="reference"><a href="#cite_note-40"><span class="cite-bracket">[</span>40<span class="cite-bracket">]</span></a></sup> Larger allocations may also increase the risk of undefined behavior due to a <a href="/wiki/Stack_overflow" title="Stack overflow">stack overflow</a>.<sup id="cite_ref-41" class="reference"><a href="#cite_note-41"><span class="cite-bracket">[</span>41<span class="cite-bracket">]</span></a></sup> C99 offered <a href="/wiki/Variable-length_arrays" class="mw-redirect" title="Variable-length arrays">variable-length arrays</a> as an alternative stack allocation mechanism –  however, this feature was relegated to optional in the later <a href="/wiki/C11_(C_standard_revision)" title="C11 (C standard revision)">C11</a> standard.</li> <li><a href="/wiki/POSIX" title="POSIX">POSIX</a> defines a function <code>posix_memalign</code> that allocates memory with caller-specified alignment. Its allocations are deallocated with <code>free</code>,<sup id="cite_ref-42" class="reference"><a href="#cite_note-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup> so the implementation usually needs to be a part of the malloc library.</li></ul> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=21" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Buffer_overflow" title="Buffer overflow">Buffer overflow</a></li> <li><a href="/wiki/Memory_debugger" title="Memory debugger">Memory debugger</a></li> <li><a href="/wiki/Memory_protection" title="Memory protection">Memory protection</a></li> <li><a href="/wiki/Page_(computer_memory)" title="Page (computer memory)">Page size</a></li> <li><a href="/wiki/Variable-length_array" title="Variable-length array">Variable-length array</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=22" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-c99-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-c99_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-c99_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) 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Retrieved <span class="nowrap">2016-01-05</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=stackoverflow.com&rft.atitle=Why+is+the+use+of+alloca%28%29+not+considered+good+practice%3F&rft_id=https%3A%2F%2Fstackoverflow.com%2Fquestions%2F1018853%2Fwhy-is-the-use-of-alloca-not-considered-good-practice&rfr_id=info%3Asid%2Fen.wikipedia.org%3AC+dynamic+memory+allocation" class="Z3988"></span></span> </li> <li id="cite_note-40"><span class="mw-cite-backlink"><b><a href="#cite_ref-40">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAmarasingheLeiserson2010" class="citation web cs1">Amarasinghe, Saman; Leiserson, Charles (2010). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150622092347/http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-172-performance-engineering-of-software-systems-fall-2010/video-lectures/lecture-8-cache-efficient-algorithms/">"6.172 Performance Engineering of Software Systems, Lecture 10"</a>. <i>MIT OpenCourseWare</i>. Massachusetts Institute of Technology. Archived from <a rel="nofollow" class="external text" href="http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-172-performance-engineering-of-software-systems-fall-2010/video-lectures/lecture-8-cache-efficient-algorithms/">the original</a> on 2015-06-22<span class="reference-accessdate">. Retrieved <span class="nowrap">2015-01-27</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=MIT+OpenCourseWare&rft.atitle=6.172+Performance+Engineering+of+Software+Systems%2C+Lecture+10&rft.date=2010&rft.aulast=Amarasinghe&rft.aufirst=Saman&rft.au=Leiserson%2C+Charles&rft_id=http%3A%2F%2Focw.mit.edu%2Fcourses%2Felectrical-engineering-and-computer-science%2F6-172-performance-engineering-of-software-systems-fall-2010%2Fvideo-lectures%2Flecture-8-cache-efficient-algorithms%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AC+dynamic+memory+allocation" class="Z3988"></span></span> </li> <li id="cite_note-41"><span class="mw-cite-backlink"><b><a href="#cite_ref-41">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://man7.org/linux/man-pages/man3/alloca.3.html">"alloca(3) - Linux manual page"</a>. <i>man7.org</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2016-01-05</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=man7.org&rft.atitle=alloca%283%29+-+Linux+manual+page&rft_id=http%3A%2F%2Fman7.org%2Flinux%2Fman-pages%2Fman3%2Falloca.3.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AC+dynamic+memory+allocation" class="Z3988"></span></span> </li> <li id="cite_note-42"><span class="mw-cite-backlink"><b><a href="#cite_ref-42">^</a></b></span> <span class="reference-text"><span class="plainlinksneverexpand"><code><a rel="nofollow" class="external text" href="https://pubs.opengroup.org/onlinepubs/9799919799/functions/posix_memalign.html">posix_memalign</a></code></span> – System Interfaces Reference, <a href="/wiki/Single_Unix_Specification" class="mw-redirect" title="Single Unix Specification">The Single UNIX Specification</a>, Version 4 from <a href="/wiki/The_Open_Group" title="The Open Group">The Open Group</a></span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=C_dynamic_memory_allocation&action=edit&section=23" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1235681985">.mw-parser-output .side-box{margin:4px 0;box-sizing:border-box;border:1px solid #aaa;font-size:88%;line-height:1.25em;background-color:var(--background-color-interactive-subtle,#f8f9fa);display:flow-root}.mw-parser-output .side-box-abovebelow,.mw-parser-output .side-box-text{padding:0.25em 0.9em}.mw-parser-output .side-box-image{padding:2px 0 2px 0.9em;text-align:center}.mw-parser-output .side-box-imageright{padding:2px 0.9em 2px 0;text-align:center}@media(min-width:500px){.mw-parser-output .side-box-flex{display:flex;align-items:center}.mw-parser-output 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Programming/C dynamic memory management">C Programming/C Reference</a></b></i></div></div> </div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1235681985"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1237033735"><div class="side-box side-box-right plainlinks sistersitebox"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409"> <div class="side-box-flex"> <div class="side-box-image"><span class="noviewer" typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Wikiversity_logo_2017.svg/40px-Wikiversity_logo_2017.svg.png" decoding="async" width="40" height="33" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Wikiversity_logo_2017.svg/60px-Wikiversity_logo_2017.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Wikiversity_logo_2017.svg/80px-Wikiversity_logo_2017.svg.png 2x" data-file-width="626" data-file-height="512" /></span></span></div> <div class="side-box-text plainlist">Wikiversity has learning resources about <i><b><a href="https://en.wikiversity.org/wiki/C/Memory_Management" class="extiw" title="v:C/Memory Management">C/Memory_Management</a></b></i></div></div> </div> <ul><li><a rel="nofollow" class="external text" href="http://www.opengroup.org/onlinepubs/9699919799/functions/malloc.html">Definition of malloc in IEEE Std 1003.1 standard</a></li> <li><a href="/wiki/Doug_Lea" title="Doug Lea">Lea, Doug</a>; <a rel="nofollow" class="external text" href="http://gee.cs.oswego.edu/dl/html/malloc.html"><i>The design of the basis of the glibc allocator</i></a></li> <li>Gloger, Wolfram; <a rel="nofollow" class="external text" href="http://www.malloc.de/en/"><i>The ptmalloc homepage</i></a></li> <li>Berger, Emery; <a rel="nofollow" class="external text" href="http://www.hoard.org/"><i>The Hoard homepage</i></a></li> <li>Douglas, Niall; <a rel="nofollow" class="external text" href="http://www.nedprod.com/programs/portable/nedmalloc/"><i>The nedmalloc homepage</i></a></li> <li>Evans, Jason; <a rel="nofollow" class="external text" href="http://jemalloc.net/"><i>The jemalloc homepage</i></a></li> <li>Google; <a rel="nofollow" class="external text" href="https://github.com/gperftools/gperftools/wiki"><i>The tcmalloc homepage</i></a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20060409094110/http://www.osdcom.info/content/view/31/39/"><i>Simple Memory Allocation Algorithms</i></a> on OSDEV Community</li> <li>Michael, Maged M.; <a rel="nofollow" class="external text" href="http://www.research.ibm.com/people/m/michael/pldi-2004.pdf"><i>Scalable Lock-Free Dynamic Memory Allocation</i></a></li> <li>Bartlett, Jonathan; <a rel="nofollow" class="external text" href="http://www.ibm.com/developerworks/library/l-memory/"><i>Inside memory management</i> – The choices, tradeoffs, and implementations of dynamic allocation</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20050823083743/http://live.gnome.org/MemoryReduction">Memory Reduction (GNOME)</a> wiki page with much information about fixing malloc</li> <li><a rel="nofollow" class="external text" href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf">C99 standard draft, including TC1/TC2/TC3</a></li> <li><a rel="nofollow" class="external text" href="http://paste.tclers.tk/1596">Some useful references about C</a></li> <li><a rel="nofollow" class="external text" href="http://www.open-std.org/jtc1/sc22/wg14/www/standards">ISO/IEC 9899 – Programming languages – C</a></li> <li><a rel="nofollow" class="external text" href="https://sploitfun.wordpress.com/2015/02/10/understanding-glibc-malloc/"><i>Understanding glibc malloc</i></a></li></ul> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style 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(TLB)</li> <li><a href="/wiki/Input%E2%80%93output_memory_management_unit" title="Input–output memory management unit">Input–output memory management unit</a> (IOMMU)</li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Virtual_memory" title="Virtual memory">Virtual memory</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Demand_paging" title="Demand paging">Demand paging</a></li> <li><a href="/wiki/Memory_paging" title="Memory paging">Memory paging</a></li> <li><a href="/wiki/Page_table" title="Page table">Page table</a></li> <li><a href="/wiki/Virtual_memory_compression" title="Virtual memory compression">Virtual memory compression</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Memory_segmentation" title="Memory segmentation">Memory segmentation</a></th><td 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title="Jemalloc">jemalloc</a></li> <li><a href="/wiki/Libumem" title="Libumem">libumem</a></li> <li><a href="/wiki/Mimalloc" title="Mimalloc">mimalloc</a></li> <li><a href="/wiki/Ptmalloc" class="mw-redirect" title="Ptmalloc">ptmalloc</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Manual_memory_management" title="Manual memory management">Manual memory management</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Static_variable" title="Static variable">Static memory allocation</a></li> <li><a class="mw-selflink selflink">C dynamic memory allocation</a></li> <li><a href="/wiki/New_and_delete_(C%2B%2B)" title="New and delete (C++)">new and delete (C++)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Garbage_collection_(computer_science)" title="Garbage collection (computer science)">Garbage collection</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Automatic_Reference_Counting" title="Automatic Reference Counting">Automatic Reference Counting</a></li> <li><a href="/wiki/Boehm_garbage_collector" title="Boehm garbage collector">Boehm garbage collector</a></li> <li><a href="/wiki/Cheney%27s_algorithm" title="Cheney's algorithm">Cheney's algorithm</a></li> <li><a href="/wiki/Concurrent_mark_sweep_collector" title="Concurrent mark sweep collector">Concurrent mark sweep collector</a></li> <li><a href="/wiki/Finalizer" title="Finalizer">Finalizer</a></li> <li><a href="/wiki/Garbage_(computer_science)" title="Garbage (computer science)">Garbage</a></li> <li><a href="/wiki/Garbage-first_collector" title="Garbage-first collector">Garbage-first collector</a></li> <li><a href="/wiki/Mark%E2%80%93compact_algorithm" title="Mark–compact algorithm">Mark–compact algorithm</a></li> <li><a href="/wiki/Reference_counting" title="Reference counting">Reference counting</a></li> <li><a href="/wiki/Tracing_garbage_collection" title="Tracing garbage collection">Tracing garbage collection</a></li> <li><a href="/wiki/Weak_reference" title="Weak reference">Strong reference</a></li> <li><a href="/wiki/Weak_reference" title="Weak reference">Weak reference</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Memory_safety" title="Memory safety">Memory safety</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Buffer_overflow" title="Buffer overflow">Buffer overflow</a></li> <li><a href="/wiki/Buffer_over-read" title="Buffer over-read">Buffer over-read</a></li> <li><a href="/wiki/Dangling_pointer" title="Dangling pointer">Dangling pointer</a></li> <li><a href="/wiki/Stack_overflow" title="Stack overflow">Stack overflow</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Issues</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fragmentation_(computing)" title="Fragmentation (computing)">Fragmentation</a></li> <li><a href="/wiki/Memory_leak" title="Memory leak">Memory leak</a></li> <li><a href="/wiki/Unreachable_memory" title="Unreachable memory">Unreachable memory</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Automatic_variable" title="Automatic variable">Automatic variable</a></li> <li><a href="/wiki/International_Symposium_on_Memory_Management" title="International Symposium on Memory Management">International Symposium on Memory Management</a></li> <li><a href="/wiki/Region-based_memory_management" title="Region-based memory management">Region-based memory management</a></li> <li><a href="/wiki/Memory_pool" title="Memory pool">Memory pool</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <a href="/wiki/Category:Memory_management" title="Category:Memory management">Memory management</a></li> <li><span class="noviewer" typeof="mw:File"><span 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