gcc/doc/gcc/known-causes-of-trouble-with-gcc/warning-messages-and-error-messages.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. index:: error messages, warnings vs errors, messages, warning and error
   7
   8 .. _warnings-and-errors:
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  10 Warning Messages and Error Messages
  11 ***********************************
  12
  13 The GNU compiler can produce two kinds of diagnostics: errors and
  14 warnings.  Each kind has a different purpose:
  15
  16 * :dfn:`Errors` report problems that make it impossible to compile your
  17   program.  GCC reports errors with the source file name and line
  18   number where the problem is apparent.
  19
  20 * :dfn:`Warnings` report other unusual conditions in your code that
  21   *may* indicate a problem, although compilation can (and does)
  22   proceed.  Warning messages also report the source file name and line
  23   number, but include the text :samp:`warning:` to distinguish them
  24   from error messages.
  25
  26 Warnings may indicate danger points where you should check to make sure
  27 that your program really does what you intend; or the use of obsolete
  28 features; or the use of nonstandard features of GNU C or C++.  Many
  29 warnings are issued only if you ask for them, with one of the :option:`-W`
  30 options (for instance, :option:`-Wall` requests a variety of useful
  31 warnings).
  32
  33 .. index:: pedantic, pedantic-errors
  34
  35 GCC always tries to compile your program if possible; it never
  36 gratuitously rejects a program whose meaning is clear merely because
  37 (for instance) it fails to conform to a standard.  In some cases,
  38 however, the C and C++ standards specify that certain extensions are
  39 forbidden, and a diagnostic *must* be issued by a conforming
  40 compiler.  The :option:`-pedantic` option tells GCC to issue warnings in
  41 such cases; :option:`-pedantic-errors` says to make them errors instead.
  42 This does not mean that *all* non-ISO constructs get warnings
  43 or errors.
  44
  45 See :ref:`warning-options`, for
  46 more detail on these and related command-line options.