6.7. Pointers to Functions

A function pointer is just that—a pointer that denotes a function rather than an object. Like any other pointer, a function pointer points to a particular type. A function’s type is determined by its return type and the types of its parameters. The function’s name is not part of its type. For example:

// compares lengths of two strings
bool lengthCompare(const string &, const string &);

has type bool(const string&, const string&). To declare a pointer that can point at this function, we declare a pointer in place of the function name:

// pf points to a function returning bool that takes two const string references
bool (*pf)(const string &, const string &);  // uninitialized

Starting from the name we are declaring, we see that pf is preceded by a *, so pf is a pointer. To the right is a parameter list, which means that pf points to a function. Looking left, we find that the type the function returns is bool. Thus, pf points to a function that has two const string& parameters and returns bool.

Image Note

The parentheses around *pf are necessary. If we omit the parentheses, then we declare pf as a function that returns a pointer to bool:

// declares a function named pf that returns a bool*
bool *pf(const string &, const string &);

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