Directive (programming) - The C Preprocessor

The C Preprocessor

In C and C++, the language supports a simple macro preprocessor. Source lines that should be handled by the preprocessor, such as #define and #include are referred to as preprocessor directives.

Another C construct, the #pragma directive, is used to instruct the compiler to use pragmatic or implementation-dependent features. Two notable users of this directive are OpenMP and OpenACC.

Syntactic constructs similar to C's preprocessor directives, such as C#'s #if, are also typically called "directives", although in these cases there may not be any real preprocessing phase involved.