A “preprocessor directive” is an instruction to the C++ preprocessor. Preprocessing takes place during the first phase of compilation. This chapter describes the preprocessing translation phase.
This chapter also discusses macros, the #define directive, the #undef directive, and the four preprocessor operators. A “preprocessor operator” is an operator that is only recognized as an operator within the context of preprocessor directives.
Include files (text files inserted into a program at the location of a #include directive), conditional compilation, the #error and #line directives, and pragmas are the topics of sections at the end of this chapter. A “pragma” is a “pragmatic,” or practical, instruction to the C++ compiler. Pragmas in C++ source files are typically used to control the actions of the compiler in a particular portion of a program without affecting the program as a whole.