Defining Overloaded Functions

Consider a database application with several functions to find a record based on name, phone number, account number, and so on. Function overloading lets us define a collection of functions, each named lookup, that differ in terms of how they do the search. We can call lookup passing a value of any of several types:

Record lookup(const Account&);  // find by Account
Record lookup(const Phone&);    // find by Phone
Record lookup(const Name&);     // find by Name

Account acct;
Phone phone;
Record r1 = lookup(acct);  // call version that takes an Account
Record r2 = lookup(phone); // call version that takes a Phone

Here, all three functions share the same name, yet they are three distinct functions. The compiler uses the argument type(s) to figure out which function to call.

Overloaded functions must differ in the number or the type(s) of their parameters. Each of the functions above takes a single parameter, but the parameters have different types.

It is an error for two functions to differ only in terms of their return types. If the parameter lists of two functions match but the return types differ, then the second declaration is an error:

Record lookup(const Account&);
bool lookup(const Account&);   // error: only the return type is different