C++ Identifiers

An identifier is a sequence of characters used to denote one of the following:

• Object or variable name
  
  
• Class, structure, or union name
  
  
• Enumerated type name
  
  
• Member of a class, structure, union, or enumeration
  
  
• Function or class-member function
  
  
• typedef name
  
  
• Label name
  
  
• Macro name
  
  
• Macro parameter

Syntax

identifier :

nondigit
identifier nondigit
identifier digit

nondigit : one of

_ a b c d e f g h i j k l m
n o p q r s t u v w x y z
A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z

digit : one of

0 1 2 3 4 5 6 7 8 9

Microsoft Specific

Only the first 247 characters of Microsoft C++ identifiers are significant. This restriction is complicated by the fact that names for user-defined types are “decorated” by the compiler to preserve type information. The resultant name, including the type information, cannot be longer than 247 characters. (See Decorated Names in the Visual C++ Programmer’s Guide for more information.) Factors that can influence the length of a decorated identifier are:

• Whether the identifier denotes an object of user-defined type or a type derived from a user-defined type.
  
  
• Whether the identifier denotes a function or a type derived from a function.
  
  
• The number of arguments to a function.

END Microsoft Specific

The first character of an identifier must be an alphabetic character, either uppercase or lowercase, or an underscore ( _ ). Because C++ identifiers are case sensitive, fileName is different from FileName.

Identifiers cannot be exactly the same spelling and case as keywords. Identifiers that contain keywords are legal. For example, Pint is a legal identifier, even though it contains int, which is a keyword.

Use of two sequential underscore characters ( __ ) at the beginning of an identifier, or a single leading underscore followed by a capital letter, is reserved for C++ implementations in all scopes. You should avoid using one leading underscore followed by a lowercase letter for names with file scope because of possible conflicts with current or future reserved identifiers.