Basic concepts

This section provides definitions for the specific terminology and the concepts used when describing the C++ programming language.

A C++ program is a sequence of text files (typically header and source files) that contain declarations . They undergo translation to become an executable program, which is executed when the C++ implementation calls its main function .

Certain words in a C++ program have special meaning, and these are known as keywords . Others can be used as identifiers . Comments are ignored during translation. C++ programs also contain literals , the values of characters inside them are determined by character sets and encodings . Certain characters in the program have to be represented with escape sequences .

The entities of a C++ program are values, objects , references , structured bindings (since C++17) , result bindings (since C++26) , functions , enumerators , types , class members, templates , template specializations , packs (since C++11) , and namespaces . Preprocessor macros are not C++ entities.

Declarations may introduce entities, associate them with names and define their properties. The declarations that define all properties required to use an entity are definitions . A program must contain only one definition of any non-inline function or variable that is odr-used .

Definitions of functions usually include sequences of statements , some of which include expressions , which specify the computations to be performed by the program.

Names encountered in a program are associated with the declarations that introduced them using name lookup . Each name is only valid within a part of the program called its scope . Some names have linkage which makes them refer to the same entities when they appear in different scopes or translation units.

Each object, reference, function, expression in C++ is associated with a type , which may be fundamental , compound, or user-defined , complete or incomplete , etc.

Declared objects and declared references that are not non-static data members are variables  .

See also

C documentation for Basic concepts