-g Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF). GDB can
work with this debugging information.
On most systems that use stabs format, -g enables use of extra debugging information that only GDB can use;
this extra information makes debugging work better in GDB but will probably make other debuggers crash or
refuse to read the program. If you want to control for certain whether to generate the extra information, use
-gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).
Unlike most other C compilers, GCC allows you to use -g with -O. The shortcuts taken by optimized code may
occasionally produce surprising results: some variables you declared may not exist at all; flow of control may
briefly move where you did not expect it; some statements may not be executed because they compute constant
results or their values were already at hand; some statements may execute in different places because they were
moved out of loops.
Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for
programs that might have bugs.
The following options are useful when GCC is generated with the capability for more than one debugging format.