Standard Template Library Programmer's Guide

Note that a function pointer of type Result (*)(Arg) is a perfectly good Unary Function object, and may be passed to an STL algorithm that expects an argument that is a Unary Function. The only reason for using the pointer_to_unary_function object is if you need to use an ordinary function in a context that requires an Adaptable Unary Function, e.g. as the argument of a function object adaptor.

Most of the time, you need not declare an object of type pointer_to_unary_function directly. It is almost always easier to construct one using the ptr_fun function.

The following code fragment replaces all of the numbers in a range with their absolute values, using the standard library function fabs . There is no need to use a pointer_to_unary_function adaptor in this case.

transform(first, last, first, fabs);

The following code fragment replaces all of the numbers in a range with the negative of their absolute values. In this case we are composing fabs and negate . This requires that fabs be treated as an adaptable unary function, so we do need to use a pointer_to_unary_function adaptor.

transform(first, last, first, compose1(negate, ptr_fun(fabs)));

Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h.

Adaptable Unary Function

• Arg is Assignable.

• Result is Assignable.

unary_function

These members are not defined in the Adaptable Unary Function requirements, but are specific to pointer_to_unary_function .

pointer_to_binary_function , ptr_fun , Adaptable Unary Function

Categories: functors, adaptors

Component type: type

Pointer_to_binary_function is a function object adaptor that allows a function pointer Result (*f)(Arg1, Arg2) to be treated as an Adaptable Binary Function . That is: if F is a pointer_to_binary_function that was initialized with an underlying function pointer f of type Result (*)(Arg1, Arg2) , then F(x, y) calls the function f(x, y) . The difference between f and F is that pointer_to_binary_function is an Adaptable Binary Function, i.e. it defines the nested typedef s first_argument_type , second_argument_type , and result_type .

Note that a function pointer of type Result (*)(Arg1, Arg2) is a perfectly good Binary Function object, and may be passed to an STL algorithm that expects an argument that is a Binary Function . The only reason for using the pointer_to_binary_function class is if you need to use an ordinary function in a context that requires an Adaptable Binary Function, e.g. as the argument of a function object adaptor.

Most of the time, you need not declare an object of type pointer_to_binary_function directly. It is almost always easier to construct one using the ptr_fun function.

The following code fragment finds the first string in a list that is equal to "OK" . It uses the standard library function strcmp as an argument to a function object adaptor, so it must first use a pointer_to_binary_function adaptor to give strcmp the Adaptable Binary Function interface.

list L;

…

list::iterator item = find_if(L.begin(), L.end(), not1(binder2nd(ptr_fun(strcmp), "OK")));

Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h.

Adaptable Binary Function

Arg1 is Assignable.

Arg2 is Assignable.

Result is Assignable.

binary_function

These members are not defined in the Adaptable Binary Function requirements, but are specific to pointer_to_binary_function .