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Standard Template Library Programmer's Guide
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pointer_to_binary_function<Arg1, Arg2, Result>



Categories: functors, adaptors	Component type: type

Description

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<Arg1, Arg2, Result> 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 typedefs 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.

Example

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

Definition

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

Template parameters

Parameter	Description	Default
`Arg1`	The function object's first argument type
`Arg2`	The function object's second argument type
`Result`	The function object's result type

Model of

Adaptable Binary Function

Type requirements

Arg1 is Assignable.
Arg2 is Assignable.
Result is Assignable.

Public base classes

binary_function<Arg1, Arg2, Result>

Members

Member	Where defined	Description
`first_argument_type`	Adaptable Binary Function	The type of the first argument: `Arg1`.
`second_argument_type`	Adaptable Binary Function	The type of the second argument: `Arg2`
`result_type`	Adaptable Binary Function	The type of the result: `Result`
`Result operator()(Arg1 x, Arg2 y)`	Binary Function	Function call operator.
`pointer_to_binary_function(Result (*f)(Arg1, Arg2))`	`pointer_to_binary_function`	See below.
`pointer_to_binary_function()`	`pointer_to_binary_function`	See below.
template <class Arg1, class Arg2, class Result> pointer_to_unary_function<Arg1, Arg2, Result> ptr_fun(Result (*x)(Arg1, Arg2));	`pointer_to_binary_function`	See below.

New members

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

Member	Description
`pointer_to_binary_function(Result (*f)(Arg1, Arg2))`	The constructor. Creates a `pointer_to_binary_function` whose underlying function is `f`.
`pointer_to_binary_function()`	The default constructor. This creates a `pointer_to_binary_function` that does not have an underlying function, and that therefore cannot actually be called.
template <class Arg1, class Arg2, class Result> pointer_to_unary_function<Arg1, Arg2, Result> ptr_fun(Result (*x)(Arg1, Arg2));	If `f` is of type `Result (*)(Arg1, Arg2)` then `ptr_fun(f)` is equivalent to `pointer_to_binary_function<Arg1,Arg2,Result>(f)`, but more convenient. This is a global function, not a member function.