#num line directives suppress warnings in C code

Question

I've been dealing with a fair amount preprocessed C code, which includes directives that look like:

#0 "/usr/local/gcctrunk/lib/gcc/x86_64unknownlinuxgnu/4.9.0/include/stddef.h" 3

The problem I've encountered is that when I compile files with such code in them using gcc, the usual warnings from the compiler are suppressed. I'm guessing that this is intended behavior? If so, is there a way to disable it (re-enabling the warnings)?

For example the testcase below produces no warnings unless the first line is commented out. Best,

------test.c-------
#0 "foo" 3

main ()
{
    printf ("%Xn");
}

Answer 1

Try -Wsystem-headers option.