C++ Notes: Function Parameters

Formal Parameters

Formal parameters are written in the function prototype and function header of the definition. Formal parameters are local variables which are assigned values from the arguments when the function is called.

Actual Parameters or Arguments

When a function is called, the values (expressions) that are passed in the call are called the arguments or actual parameters (both terms mean the same thing). At the time of the call each actual parameter is assigned to the corresponding formal parameter in the function definition.

For value parameters (the default), the value of the actual parameter is assigned to the formal parameter variable. For reference parameters, the memory address of the actual parameter is assigned to the formal parameter.

Value Parameters

By default, argument values are simply copied to the formal parameter variables at the time of the call. This type of parameter passing is called pass-by-value. It is the only kind of parameter passing in Java and C. C++ also has pass-by-reference (see below).

Reference Parameters

A reference parameter is indicated by following the formal parameter name in the function prototype/header by an ampersand (&). The compiler will then pass the memory address of the actual parameter, not the value. A formal reference parameter may be used as a normal variable, without explicit dereference - the compiler will generate the correct code for using an address. Reference parameters are useful in two cases: See Reference Parameters.

Additional topics

This summary doesn't cover some features: eg, variable parameter lists, default parameter values, ....