7 Expressions [expr]

A function call is a postfix expression followed by parentheses containing a possibly empty, comma-separated list of initializer-clauses which constitute the arguments to the function.

The postfix expression shall have function type or function pointer type.

For a call to a non-member function or to a static member function, the postfix expression shall be either an lvalue that refers to a function (in which case the function-to-pointer standard conversion ([conv.func]) is suppressed on the postfix expression), or a prvalue of function pointer type.

If the selected function is non-virtual, or if the id-expression in the class member access expression is a qualified-id, that function is called.

Otherwise, its final overrider in the dynamic type of the object expression is called; such a call is referred to as a virtual function call.

If the postfix-expression names a destructor or pseudo-destructor ([expr.prim.id.dtor]), the type of the function call expression is void; otherwise, the type of the function call expression is the return type of the statically chosen function (i.e., ignoring the virtual keyword), even if the type of the function actually called is different.

If the postfix-expression names a pseudo-destructor (in which case the postfix-expression is a possibly-parenthesized class member access), the function call destroys the object of scalar type denoted by the object expression of the class member access ([expr.ref], [basic.life]).

A type ${\text{T}}_{\text{call}}$ is call-compatible with a function type ${\text{T}}_{\text{func}}$ if ${\text{T}}_{\text{call}}$ is the same type as ${\text{T}}_{\text{func}}$ or if the type “pointer to ${\text{T}}_{\text{func}}$” can be converted to type “pointer to ${\text{T}}_{\text{call}}$” via a function pointer conversion ([conv.fctptr]).

Calling a function through an expression whose function type is not call-compatible with the type of the called function's definition results in undefined behavior.

When a function is called, each parameter ([dcl.fct]) is initialized ([dcl.init], [class.copy.ctor]) with its corresponding argument.

If the function is an explicit object member function and there is an implied object argument ([over.call.func]), the list of provided arguments is preceded by the implied object argument for the purposes of this correspondence.

If there is no corresponding argument, the default argument for the parameter is used.

If the function is an implicit object member function, the object expression of the class member access shall be a glvalue and the implicit object parameter of the function ([over.match.funcs]) is initialized with that glvalue, converted as if by an explicit type conversion.

When a function is called, the type of any parameter shall not be a class type that is either incomplete or abstract.

It is implementation-defined whether a parameter is destroyed when the function in which it is defined exits ([stmt.return], [except.ctor]) or at the end of the enclosing full-expression; parameters are always destroyed in the reverse order of their construction.

The initialization and destruction of each parameter occurs within the context of the full-expression ([intro.execution]) where the function call appears.

The postfix-expression is sequenced before each expression in the expression-list and any default argument.

The initialization of a parameter, including every associated value computation and side effect, is indeterminately sequenced with respect to that of any other parameter.

The result of a function call is the result of the possibly-converted operand of the return statement ([stmt.return]) that transferred control out of the called function (if any), except in a virtual function call if the return type of the final overrider is different from the return type of the statically chosen function, the value returned from the final overrider is converted to the return type of the statically chosen function.

A function can be declared to accept fewer arguments (by declaring default arguments) or more arguments (by using the ellipsis, ..., or a function parameter pack ([dcl.fct])) than the number of parameters in the function definition.

When there is no parameter for a given argument, the argument is passed in such a way that the receiving function can obtain the value of the argument by invoking va_arg.

The lvalue-to-rvalue, array-to-pointer, and function-to-pointer standard conversions are performed on the argument expression.

An argument that has type cv std​::​nullptr_t is converted to type void* ([conv.ptr]).

After these conversions, if the argument does not have arithmetic, enumeration, pointer, pointer-to-member, or class type, the program is ill-formed.

Passing a potentially-evaluated argument of a scoped enumeration type ([dcl.enum]) or of a class type ([class]) having an eligible non-trivial copy constructor ([special], [class.copy.ctor]), an eligible non-trivial move constructor, or a non-trivial destructor ([class.dtor]), with no corresponding parameter, is conditionally-supported with implementation-defined semantics.

If the argument has integral or enumeration type that is subject to the integral promotions, or a floating-point type that is subject to the floating-point promotion, the value of the argument is converted to the promoted type before the call.

These promotions are referred to as the default argument promotions.

Recursive calls are permitted, except to the main function.

A function call is an lvalue if the result type is an lvalue reference type or an rvalue reference to function type, an xvalue if the result type is an rvalue reference to object type, and a prvalue otherwise.