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<title>Using the GNU Compiler Collection (GCC)</title>
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<h3 class="section">Warning Messages and Error Messages</h3>
<p>The GNU compiler can produce two kinds of diagnostics: errors and
warnings. Each kind has a different purpose:
<ul>
<li><dfn>Errors</dfn> report problems that make it impossible to compile your
program. GCC reports errors with the source file name and line
number where the problem is apparent.
<li><dfn>Warnings</dfn> report other unusual conditions in your code that
<em>may</em> indicate a problem, although compilation can (and does)
proceed. Warning messages also report the source file name and line
number, but include the text <code>warning:</code> to distinguish them
from error messages.
</ul>
<p>Warnings may indicate danger points where you should check to make sure
that your program really does what you intend; or the use of obsolete
features; or the use of nonstandard features of GNU C or C++. Many
warnings are issued only if you ask for them, with one of the <code>-W</code>
options (for instance, <code>-Wall</code> requests a variety of useful
warnings).
<p>GCC always tries to compile your program if possible; it never
gratuitously rejects a program whose meaning is clear merely because
(for instance) it fails to conform to a standard. In some cases,
however, the C and C++ standards specify that certain extensions are
forbidden, and a diagnostic <em>must</em> be issued by a conforming
compiler. The <code>-pedantic</code> option tells GCC to issue warnings in
such cases; <code>-pedantic-errors</code> says to make them errors instead.
This does not mean that <em>all</em> non-ISO constructs get warnings
or errors.
<p>See <a href="Warning-Options.html#Warning%20Options">Options to Request or Suppress Warnings</a>, for
more detail on these and related command-line options.
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