15.6 Warning Messages and Error Messages

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. GNU Fortran reports errors with the source file name, line number, and column within the line where the problem is apparent.
• Warnings report other unusual conditions in your code that might indicate a problem, although compilation can (and does) proceed. Warning messages also report the source file name, line number, and column information, but include the text `warning:' to distinguish them from error messages.

Warnings might 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 Fortran. 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).

Note: Currently, the text of the line and a pointer to the column is printed in most g77 diagnostics.

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