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<h3 class="section">12.5 Standard Libraries</h3>
<p><a name="index-Wall-4270"></a>GCC by itself attempts to be a conforming freestanding implementation.
See <a href="Standards.html#Standards">Language Standards Supported by GCC</a>, for details of
what this means. Beyond the library facilities required of such an
implementation, the rest of the C library is supplied by the vendor of
the operating system. If that C library doesn't conform to the C
standards, then your programs might get warnings (especially when using
<samp><span class="option">-Wall</span></samp>) that you don't expect.
<p>For example, the <code>sprintf</code> function on SunOS 4.1.3 returns
<code>char *</code> while the C standard says that <code>sprintf</code> returns an
<code>int</code>. The <code>fixincludes</code> program could make the prototype for
this function match the Standard, but that would be wrong, since the
function will still return <code>char *</code>.
<p>If you need a Standard compliant library, then you need to find one, as
GCC does not provide one. The GNU C library (called <code>glibc</code>)
provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for
GNU/Linux and HURD-based GNU systems; no recent version of it supports
other systems, though some very old versions did. Version 2.2 of the
GNU C library includes nearly complete C99 support. You could also ask
your operating system vendor if newer libraries are available.
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