Compiling for Debugging
In order to debug a program effectively, you need to generate debugging information when you compile it. This debugging information is stored in the object file; it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code.9
To request debugging information, specify the -g option when you run the compiler.
Many C compilers are unable to handle the -g and -O options together. Using those compilers, you cannot generate optimized executables containing debugging information.
GCC, the GNU C compiler, supports -g with or without -O, making it possible to debug optimized code. We recommend that you always use -g whenever you compile a program. You may think your program is correct, but there is no sense in pushing your luck.
When you debug a program compiled with -g -O, remember that the optimizer is rearranging your code; the debugger shows you what is really there. Do not be too surprised when the execution path does not exactly match your source file! An extreme example: if you define a variable, but never use it, DDD never sees that variable--because the compiler optimizes it out of existence.
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