When the compiler encounters a programming error while compiling a C source program, it issues a diagnostic message to the standard error device, or to a listing file if you compile with the -qsource option. These diagnostic messages are specific to the C language.
If you specify the compiler option -qsrcmsg and the error is applicable to a particular line of code, the reconstructed source line or partial source line is included with the error message. A reconstructed source line is a preprocessed source line that has all the macros expanded.
You can control the diagnostic messages issued, according to their severity, using either the -qflag option or the -w option. To get additional informational messages about potential problems in your program, use the -qinfo option.