On a Red Hat Enterprise Linux 4 WS system

freak:~/drv/helloworld % echo helloworld | cpp -dM | more
#define __DBL_MIN_EXP__ (-1021)
#define __FLT_MIN__ 1.17549435e-38F
...

Only platform specific macros are given. For standard macros, see RHEL-4 GCC manual section about macros.