Preprocessor

The preprocessor runs before the compilation begins. The result of preprocessing is single file which is then passed to the actual compiler.

[edit] Directives

The preprocessing directives control the behavior of the preprocessor. Each directive occupies one line and has the following format:

• # character
• preprocessing instruction (one of define, undef, include, if, ifdef, ifndef, else, elif, endif, line, error, warning, pragma)
• arguments (depends on the instruction)
• line break

The null directive (# followed by a line break) is allowed and has no effect.

[edit] Capabilities

The preprocessor has the source file translation capabilities:

• conditionally compile of parts of source file (controlled by directive #if, #ifdef, #ifndef, #else, #elif and #endif).
• replace text macros while possibly concatenating or quoting identifiers (controlled by directives #define and #undef, and operators # and ##)
• include other files (controlled by directive #include)
• cause a warning (controlled by directive #warning)
• cause an error (controlled by directive #error)

The following aspects of the preprocessor can be controlled:

• implementation defined behavior (controlled by directives #pragma)
• file name and line information available to the preprocessor (controlled by directives #line)