Software Engineering and Computer Games

22.15. Preprocessor directives

Compiling a file is actually a multi-step process. Before actually compiling any code, a compiler uses something called a ‘preprocessor’ to look through the project files and carries out the instructions embodied in the various preprocessor directives. Any line of C++ that starts with # is a preprocessor directive. Some of them are #include, #define, #ifdef, #endif, and #pragma. Each preprocessor directive tells the compiler to do something before running. The instructions in the # directives are used to alter the contents of the file, which is only then passed on to the normal compilation process.

The #include directive

What the #include directive tells the compiler to do is to replace a line like #include “whatever.h” ...