Primary Expressions

Primary expressions are the building blocks of more complex expressions. They may be literals, names, and names qualified by the scope-resolution operator (::). A primary expression may have any of the following forms:

:: name ( expression )

A literal is a constant primary expression. Its type depends on the form of its specification. For complete information about specifying literals, see Literals .

The this keyword is a pointer to a class object. It's available within nonstatic member functions. It points to the instance of the class for which the function was invoked. The this keyword can't be used outside the body of a class-member function.

The type of the this pointer is type * const (where type is the class name) within functions that don't specifically modify the this pointer. The following example shows member function declarations and the types of this:

// expre_Primary_Expressions.cpp
// compile with: /LD
class Example
    void Func();          //  * const this
    void Func() const;    //  const * const this
    void Func() volatile; //  volatile * const this

For more information about modifying the type of the this pointer, see this pointer.

The scope-resolution operator (::) followed by a name is a primary expression. Such names must be names at global scope, not member names. The type of the expression is determined by the declaration of the name. It's an l-value (that is, it can appear on the left-hand side of an assignment expression) if the declaring name is an l-value. The scope-resolution operator allows a global name to be referred to, even if that name is hidden in the current scope. See Scope for an example of how to use the scope-resolution operator.

An expression enclosed in parentheses is a primary expression. Its type and value are identical to the type and value of the unparenthesized expression. It's an l-value if the unparenthesized expression is an l-value.

Examples of primary expressions include:

100 // literal
'c' // literal
this // in a member function, a pointer to the class instance
::func // a global function
::operator + // a global operator function
::A::B // a global qualified name
( i + 1 ) // a parenthesized expression

These examples are all considered names, and as such, primary expressions, in various forms:

MyClass // an identifier
MyClass::f // a qualified name
operator = // an operator function name
operator char* // a conversion operator function name
~MyClass // a destructor name
A::B   // a qualified name
A<int> // a template id

See also

Types of Expressions