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class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/performance/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Performance</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/storage/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Database bindings (SQLite, KV, …)</a></li> <li class="toctree-l1 current"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">XPCOM</a> <ul class="current"> <li class="toctree-l2"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#consuming-xpcom-functionality">Consuming XPCOM functionality</a></li> <li class="toctree-l2"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#tooling-around-xpcom">Tooling around XPCOM</a></li> <li class="toctree-l2 current"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#writing-new-xpcom-interfaces-classes">Writing new XPCOM interfaces/classes</a> <ul class="current"> <li class="toctree-l3"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/xpidl.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">XPIDL</a></li> <li class="toctree-l3"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/writing-xpcom-interface.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Tutorial for Writing a New XPCOM Interface</a></li> <li class="toctree-l3"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/cc-macros.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">How to make a C++ class cycle collected</a></li> <li class="toctree-l3 current"><a class="current reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#"><code class="docutils literal notranslate">{fmt}</code> in Gecko</a></li> <li class="toctree-l3"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#user-defined-types">User-defined types</a></li> <li class="toctree-l3"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#formatting-sequences">Formatting sequences</a></li> <li class="toctree-l3"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#moz-log-integration"><code class="docutils literal notranslate">MOZ_LOG</code> integration</a></li> <li class="toctree-l3"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#ns-string-integration"><code class="docutils literal notranslate">ns*String</code> integration</a></li> <li class="toctree-l3"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#useful-links">Useful links</a></li> </ul></li> </ul></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/nspr/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">NSPR</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/security/nss/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Network Security Services (NSS)</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/content-security/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Web Security Checks in Gecko</a></li> </ul> The Firefox Build System <ul> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/mach/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Mach</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/tools/try/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Pushing to Try</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/build/buildsystem/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Build System</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/taskcluster/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Firefox CI and Taskgraph</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/tools/moztreedocs/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Managing Documentation</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/mozbuild/vendor/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Vendoring Third Party Components</a></li> </ul> Testing & Test Infrastructure <ul> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/testing/automated-testing/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Automated Testing</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/testing/treeherder-try/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Understanding Treeherder Results</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/testing/sheriffed-intermittents/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Sheriffed intermittent failures</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/testing/tests-for-new-config/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Turning on Firefox tests for a new configuration</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/testing/intermittent/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Avoiding intermittent tests</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/testing/testing-policy/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Testing Policy</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/testing/ci-configs/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Configuration Changes</a></li> <li class="toctree-l1"><a class="reference internal" href="https://firefox--source--docs-mozilla-org.translate.goog/testing/browser-chrome/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Browser chrome mochitests</a></li> <li class="toctree-l1"><a class="reference internal" 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href="https://firefox--source--docs-mozilla-org.translate.goog/metrics/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Metrics</a></li> </ul> </div> </div> </nav> <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap"> <nav class="wy-nav-top" aria-label="Mobile navigation menu"> <a href="https://firefox--source--docs-mozilla-org.translate.goog/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">Firefox Source Docs</a> </nav> <div class="wy-nav-content"> <div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="https://firefox--source--docs-mozilla-org.translate.goog/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item"><a href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB">XPCOM</a></li> <li class="breadcrumb-item active"><code class="docutils literal notranslate">{fmt}</code> in Gecko</li> <li class="wy-breadcrumbs-aside"><a href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://bugzilla.mozilla.org/enter_bug.cgi?product%3DDeveloper%2BInfrastructure%26component%3DFirefox%2BSource%2BDocs%253A%2BContent%26short_desc%3DDocumentation%2Bissue%2Bon%2Bxpcom/fmt-in-gecko%26comment%3DURL%2B%3D%2Bhttps://firefox-source-docs.mozilla.org/xpcom/fmt-in-gecko.html%26bug_file_loc%3Dhttps://firefox-source-docs.mozilla.org/xpcom/fmt-in-gecko.html" rel="nofollow">Report an issue</a> / <a href="https://firefox--source--docs-mozilla-org.translate.goog/_sources/xpcom/fmt-in-gecko.md.txt?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB" rel="nofollow"> View page source</a></li> </ul> <hr> </div> <div role="main" class="document" itemscope itemtype="http://schema.org/Article"> <div itemprop="articleBody"> <section id="fmt-in-gecko"> <h1><code class="docutils literal notranslate">{fmt}</code> in Gecko<a class="headerlink" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#fmt-in-gecko" title="Link to this heading">¶</a></h1> <a class="reference external" href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://fmt.dev/"><code class="docutils literal notranslate">{fmt}</code></a> is a library implementation of C++20’s <a class="reference external" href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://en.cppreference.com/w/cpp/header/format"><code class="docutils literal notranslate">std::format</code></a> formatting API which enables type-informed string formatting. Unlike <code class="docutils literal notranslate">printf</code> this format string style does not require specifying the types of each format parameter in the format string. For example, instead of: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>#include <mozilla/Sprintf.h> #include <inttypes.h> // ... char buf[1024]; int64_t a = 123; uint64_t a = 456; auto literal = "A literal"_ns; mozilla::SprintfBuf(buf, 1024, "Formatting a number: %" PRId64 " and another one: " PRIu64 ", and finally a string: %s", a, b, literal.get()); </pre> </div> </div> one can do: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>#include <fmt/format.h> // ... char buf[1024]; int64_t a = 123; uint64_t a = 456; auto literal = "A literal"_ns; fmt::format_to_n(res, 1024, FMT_STRING("Formatting a number: {} and another one: {} " "and finally a string: {}"), a, b, literal.get()); </pre> </div> </div> </section> <section id="user-defined-types"> <h1>User-defined types<a class="headerlink" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#user-defined-types" title="Link to this heading">¶</a></h1> Formatting a <a class="reference external" href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://fmt.dev/11.0/api/%23formatting-user-defined-types">user-defined type</a> can be done once, and then used with all sorts of formatting function in <code class="docutils literal notranslate">{fmt}</code>. Given an example object: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>struct POD { double mA; uint64_t mB; }; </pre> </div> </div> one can write a custom formatter like so: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>auto format_as(POD aInstance) -> std::string { return fmt::format(FMT_STRING("POD: mA: {}, mB: {}"), aInstance.mA, aInstance.mB); } </pre> </div> </div> and use it as expected in a variety of ways: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>char bufFmt[1024] = {}; POD p{4.3, 8}; auto [out, size] = fmt::format_to(bufFmt, "{}", p); *out = 0; // Write the null terminator assert(!strcmp("POD: mA: 4.3, mB: 8", bufFmt)); fmt::println(FMT_STRING("### debug: {}"), p); fmt::print(stderr, FMT_STRING("### debug to stderr {}\n"), p); MOZ_LOG_FMT(gLogModule, "Important: {}", p); </pre> </div> </div> </section> <section id="formatting-sequences"> <h1>Formatting sequences<a class="headerlink" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#formatting-sequences" title="Link to this heading">¶</a></h1> Containers that can work with with range-based for-loop can be formatted easily: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>nsTArray<uint8_t> array(4); for (uint32_t i = 0; i < 4; i++) { array.AppendElement((123 * 5 * (i+1)) % 255); } auto [out, size] = fmt::format_to(bufFmt, FMT_STRING("{:#04x}"), fmt::join(array, ", ")); *out = 0; // Write the null terminator ASSERT_STREQ("0x69, 0xd2, 0x3c, 0xa5", bufFmt); </pre> </div> </div> </section> <section id="moz-log-integration"> <h1><code class="docutils literal notranslate">MOZ_LOG</code> integration<a class="headerlink" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#moz-log-integration" title="Link to this heading">¶</a></h1> <code class="docutils literal notranslate">MOZ_LOG_FMT</code> is like <code class="docutils literal notranslate">MOZ_LOG</code>, but takes an <code class="docutils literal notranslate">{fmt}</code>-style format string: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>MOZ_LOG_FMT(gLogModule, "{}x{} = {}", 3, 3, 3*3); </pre> </div> </div> Unlike with <code class="docutils literal notranslate">MOZ_LOG</code>, it is unnecessary to put an extra pair of parenthesis around the format and argument list. </section> <section id="ns-string-integration"> <h1><code class="docutils literal notranslate">ns*String</code> integration<a class="headerlink" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#ns-string-integration" title="Link to this heading">¶</a></h1> It is possible to append an <code class="docutils literal notranslate">{fmt}</code>-style format string to an <code class="docutils literal notranslate">nsString</code> like so: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>nsCString aLovelyString("Here is a value: "); aLovelyString.AppendFmt(FMT_SRING("{}"), 4); nsString aLovelyWideString(u"Here are two values: "); aLovelyString.AppendFmt(FMT_SRING(u"{}, {}"), 4, u"wide"); </pre> </div> </div> Or directly use <code class="docutils literal notranslate">nsFmt[C]String</code>: <div class="highlight-c++ notranslate"> <div class="highlight"> <pre>nsFmtCString str(FMT_STRING("{},{},{},{}"), 1, 1, 2, 3); nsFmtString str(FMT_STRING(u"{},{},{},{}"), 1, 1, 2, u"wide string"); // use it as usual </pre> </div> </div> </section> <section id="useful-links"> <h1>Useful links<a class="headerlink" href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/fmt-in-gecko.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB#useful-links" title="Link to this heading">¶</a></h1> <ul class="simple"> <li>The syntax of <code class="docutils literal notranslate">{fmt}</code> format string: <a class="reference external" href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://fmt.dev/latest/syntax/">https://fmt.dev/latest/syntax/</a></li> <li>The complete API of the library: <a class="reference external" href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://fmt.dev/latest/api/">https://fmt.dev/latest/api/</a></li> </ul> </section> </div> </div> <footer> <div class="rst-footer-buttons" role="navigation" aria-label="Footer"><a href="https://firefox--source--docs-mozilla-org.translate.goog/xpcom/cc-macros.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB" class="btn btn-neutral float-left" title="How to make a C++ class cycle collected" accesskey="p" rel="prev"> Previous</a> <a href="https://firefox--source--docs-mozilla-org.translate.goog/nspr/index.html?_x_tr_sl=pl&_x_tr_tl=iw&_x_tr_hl=en-GB" class="btn btn-neutral float-right" title="NSPR" accesskey="n" rel="next">Next </a> </div> <hr> <div role="contentinfo"> </div> Built with <a href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://www.sphinx-doc.org/">Sphinx</a> using a <a href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://github.com/readthedocs/sphinx_rtd_theme">theme</a> provided by <a href="https://translate.google.com/website?sl=pl&tl=iw&hl=en-GB&u=https://readthedocs.org">Read the Docs</a>. </footer> </div> </div> </section> </div> <script> jQuery(function () { SphinxRtdTheme.Navigation.enable(true); 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