Functions are named units of computation and are essential to structuring even modest programs. Every function has a return type, a name, a (possibly empty) list of parameters, and a function body. The function body is a block that is executed when the function is called. When a function is called, the arguments passed to the function must be compatible with the types of the corresponding parameters.

In C++, functions may be overloaded: The same name may be used to define different functions as long as the number or types of the parameters in the functions differ. The compiler automatically figures out which function to call based on the arguments in a call. The process of selecting the right function from a set of overloaded functions is referred to as function matching.