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(gcc-295.info)Warnings and Errors

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Warning Messages and Error Messages
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   The GNU compiler can produce two kinds of diagnostics: errors and
warnings.  Each kind has a different purpose:

     *Errors* 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.

     *Warnings* report other unusual conditions in your code that *may*
     indicate a problem, although compilation can (and does) proceed.
     Warning messages also report the source file name and line number,
     but include the text `warning:' to distinguish them from error
     messages.

   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 `-W'
options (for instance, `-Wall' requests a variety of useful warnings).

   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 *must* be issued by a conforming compiler.
The `-pedantic' option tells GCC to issue warnings in such cases;
`-pedantic-errors' says to make them errors instead.  This does not
mean that *all* non-ANSI constructs get warnings or errors.

   Note: Options to Request or Suppress Warnings, for
more detail on these and related command-line options.