C++ In a Nutshell

Name

#define directive — Defines a macro

Synopsis

#define identifier 
               definition
#define identifier(  ) definition
#define identifier(  ) definition
#define identifier(identifier-list) definition
            

The #define directive defines a macro named identifier. The macro’s replacement text is the list of tokens shown as definition. The macro can be simple, with no arguments, or can have an argument list. The argument list is introduced by a left parenthesis that immediately follows the macro name. If there is a space between identifier and (, the ( is interpreted as the start of the definition of a simple macro. The identifier-list can be empty, or it can be a list of identifiers separated by commas. Whitespace is permitted in the identifier-list and before the closing parenthesis.

C programmers are accustomed to using macros to declare constants and simple inline functions, but C++ offers const declarations, true inline functions, and templates. Macros are therefore used much less often in C++ than in C. The main drawback to macros is that they do not obey scope or namespace rules. When you must use macros, a common convention is to use all uppercase letters for the macro names, and never use all uppercase letters for non-macro names.

A macro’s scope is from the point of definition to the end of the source file, or until you undefine the macro with the #undef directive. If you try to repeat a macro definition, the new definition must be identical to the original definition. The only way to give ...