cppflags

CPPFLAGS stands for C PreProcessor Flags. It is an environment variable and a make variable used by many build systems to pass options to the preprocessor stage of the compiler. CPPFLAGS typically affects both C and C++ sources by providing include paths, macro definitions, and other preprocessor directives.

Common uses of CPPFLAGS include adding include directories with -I, defining or undefining macros with -D and -U, and specifying system include directories with -isystem. Other preprocessor-related options, such as -include to force include a file before processing, can also be supplied via CPPFLAGS. These flags influence header resolution and macro expansion before the compiler proper processes the source code.

CPPFLAGS is distinct from CFLAGS and CXXFLAGS. CFLAGS (and CXXFLAGS for C++) contain compiler options that influence optimization, warnings, and language features during the actual compilation of source code, after preprocessing. LDFLAGS holds options passed to the linker during the linking stage. In many Autotools-based projects, the build system uses CPPFLAGS to accumulate preprocessor options and CFLAGS/CXXFLAGS for compilation options separately.

Setting CPPFLAGS can be done in the environment or on the make command line. For example, CPPFLAGS="-I /opt/include -DDEBUG" ./configure or make CPPFLAGS="-I /opt/include" will ensure those preprocessor options are applied when building the project. While CPPFLAGS is widely supported, some projects may implement their own conventions or use alternative variables; the core idea remains: it collects preprocessor-related flags to be applied during compilation.