Standard Template Library Programmer's Guide

[1] Intuitively, you can think of this operation as "binding" the first argument of a binary function to a constant, thus yielding a unary function. This is a special case of a closure.

The function object overview, binder2nd , Adaptable Unary Function, Adaptable Binary Function

Categories: functors, adaptors

Component type: type

Binder2nd is a function object adaptor: it is used to transform an adaptable binary function into an adaptable unary function. Specifically, if f is an object of class binder2nd , then f(x) returns F(x, c) , where F is an object of class AdaptableBinaryFunction and where c is a constant. Both F and c are passed as arguments to binder2nd 's constructor. [1]

The easiest way to create a binder2nd is not to call the constructor explicitly, but instead to use the helper function bind2nd .

Finds the first positive number in a list.

list L;

…

list::iterator first_positive = find_if(L.begin(), L.end(), bind2nd(greater(), 0));

assert(first_positive == L.end() || *first_positive > 0);

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

Adaptable Unary Function

AdaptableBinaryFunction must be a model of Adaptable Binary Function.

unary_function

These members are not defined in the Adaptable Unary Function requirements, but are specific to binder2nd .

[1] Intuitively, you can think of this operation as "binding" the second argument of a binary function to a constant, thus yielding a unary function. This is a special case of a closure.

The function object overview, binder1st , Adaptable Unary Function, Adaptable Binary Function

Categories: functors, adaptors

Component type: function

template

pointer_to_unary_function ptr_fun(Result (*x)(Arg));

template

pointer_to_binary_function ptr_fun(Result (*x)(Arg1, Arg2));

Ptr_fun takes a function pointer as its argument and returns a function pointer adaptor, a type of function object. It is actually two different functions, not one (that is, the name ptr_fun is overloaded). If its argument is of type Result (*)(Arg) then ptr_fun creates a pointer_to_unary_function , and if its argument is of type Result (*)(Arg1, Arg2) then ptr_fun creates a pointer_to_binary_function .

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

The argument must be a pointer to a function that takes either one or two arguments. The argument type(s) and the return type of the function are arbitrary, with the restriction that the function must return a value; it may not be a void function.

See the examples in the discussions of pointer_to_unary_function and pointer_to_binary_function .

Function Objects, pointer_to_unary_function , pointer_to_binary_function , Adaptable Unary Function, Adaptable Binary Function

Categories: functors, adaptors

Component type: type

Pointer_to_unary_function is a function object adaptor that allows a function pointer Result (*f)(Arg) to be treated as an Adaptable Unary Function. That is: if F is a pointer_to_unary_function that was initialized with an underlying function pointer f of type Result (*)(Arg) , then F(x) calls the function f(x) . The difference between f and F is that pointer_to_unary_function is an Adaptable Unary Function, i.e. it defines the nested typedef s argument_type and result_type .