8.18 C++ compiler says "NULL redefined"

Q: When I compile a C++ program which includes some standard C header files, the compiler prints error messages about redefinition of NULL....

A: This is because GCC 2.8.1 comes with C++ header files which redefine NULL in a way that conflicts with the DJGPP headers. It's a bug in the GNU C++ headers, but until it is fixed, you will need to make sure you include the C++ headers after the C headers. If that doesn't help in your case, you will need to hack your headers to reconcile them.

The C header files that come with DJGPP v2.02 work around this problem, so upgrading to the latest DJGPP release should make these messages go away.