Macros

A macro is a fragment of code which has been given a name. Whenever the name is used, it is replaced by the contents of the macro. There are two kinds of macros. They differ mostly in what they look like when they are used. Object-like macros resemble data objects when used, function-like macros resemble function calls.

You may define any valid identifier as a macro, even if it is a C keyword. The preprocessor does not know anything about keywords. This can be useful if you wish to hide a keyword such as const from an older compiler that does not understand it. However, the preprocessor operator defined (see Defined) can never be defined as a macro, and C++’s named operators (see C++ Named Operators) cannot be macros when you are compiling C++.

• Object-like Macros
• Function-like Macros
• Macro Arguments
• Stringizing
• Concatenation
• Variadic Macros
• Predefined Macros
  • Standard Predefined Macros
  • Common Predefined Macros
  • System-specific Predefined Macros
  • C++ Named Operators
• Undefining and Redefining Macros
• Directives Within Macro Arguments
• Macro Pitfalls
  • Misnesting
  • Operator Precedence Problems
  • Swallowing the Semicolon
  • Duplication of Side Effects
  • Self-Referential Macros
  • Argument Prescan
  • Newlines in Arguments