These variables are usually set inside a Makefile and are then appended to the command line when the compiler is invoked. If they are not specified in the Makefile, then they will be read from the environment, if present. Tools like autoconf's ./configure script will usually pick them up from the environment and write them into the generated Makefiles.
CFLAGS allows to add switches for the C compiler, while CXXFLAGS is meant to be used when invoking a C++ compiler. Similarly, a variable CPPFLAGS exists with switches to be passed to the C preprocessor.
Hands on - Linux/Unix - Make way for movies. Find out how the Xine project can help you play DVDs and other video files on Linux.(Column)
May 01, 2005; Byline: Barry Shilliday. DVD playback on Linux has, for a long time, been troublesome; no distributions support it on a plain...