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    <p>libstdc++ does define <code>__USE_MINGW_ANSI_STDIO</code> during build (<code>config/os/mingw32-w64/os_defines.h</code>), which will turn on the mingw <code>sprintf</code> wrapper. As @Michael Burr pointed out, these wrappers exist for C99/GNU99 compatibility.</p> <p>Your test does not define <code>__USE_MINGW_ANSI_STDIO</code>, hence you'll not get the wrapper with <code>stdio.h</code>. But since it was defined when building libstdc++, you'll get it with <code>cstdio</code>. If you however define it yourself before including <code>stdio.h</code>, you will get the wrapper again.</p> <p>So you do get in fact different implementations, and <code>cstdio std::sprintf</code> is not necessarily the same as <code>stdio.h sprintf</code>, at least not when it comes to mingw.</p> <p>Here is a test. First the source:</p> <pre><code>#ifdef USE_STDIO #include &lt;stdio.h&gt; #else #include &lt;cstdio&gt; using std::sprintf; #endif int main () { int i; for (i = 0; i &lt; 500000; i++){ char x[100]; sprintf(x, "x%dx%dx", i, i&lt;&lt;2); } } </code></pre> <p>Results:</p> <pre><code>$ g++ -o test_cstdio.exe test.cc $ g++ -o test_stdio.exe -DUSE_STDIO test.cc $ g++ -o test_stdio_wrap.exe -DUSE_STDIO -D__USE_MINGW_ANSI_STDIO test.cc $ for x in test_*.exe; do ( echo $x; objdump -d $x | grep sprintf; echo ); done test_cstdio.exe 40154a: e8 41 64 00 00 callq 407990 &lt;_Z7sprintfPcPKcz&gt; 0000000000402c40 &lt;__mingw_vsprintf&gt;: 0000000000407990 &lt;_Z7sprintfPcPKcz&gt;: 4079c8: e8 73 b2 ff ff callq 402c40 &lt;__mingw_vsprintf&gt; test_stdio.exe 40154a: e8 71 62 00 00 callq 4077c0 &lt;sprintf&gt; 00000000004077c0 &lt;sprintf&gt;: 4077c0: ff 25 6e 6c 00 00 jmpq *0x6c6e(%rip) # 40e434 &lt;__imp_sprintf&gt; test_stdio_wrap.exe 40154a: e8 41 64 00 00 callq 407990 &lt;_Z7sprintfPcPKcz&gt; 0000000000402c40 &lt;__mingw_vsprintf&gt;: 0000000000407990 &lt;_Z7sprintfPcPKcz&gt;: 4079c8: e8 73 b2 ff ff callq 402c40 &lt;__mingw_vsprintf&gt; </code></pre>
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