Standard Template Library Programmer's Guide

Pair	The function object's argument type.

Model of

Adaptable Unary Function

Type requirements

There exist some types U and V such that Pair provides the same interface as a pair<U,V>. [1]

Public base classes

unary_function<Pair, Pair::first_type>

Members

Member	Where defined	Description
argument_type	Adaptable Unary Function	The type of select1st 's argument: Pair
result_type	Adaptable Unary Function The type of the result:	Pair::first_type
const Pair::first_type& operator()(const Pair& p) const	Adaptable Unary Function	Function call. The return value is p.first.

New members

All of select1st's members are defined in the Adaptable Unary Function requirements. Select1st does not introduce any new members.

Notes

[1] Pair is not actually required to be a pair<U,V> , but merely to support the same interface as pair. In almost all cases the template parameter will be a pair, but it is occasionally useful for it to be something else. One example is a struct that has the members first, second, and third.

See also

identity, select2nd, project1st, project2nd

select2nd<Pair>

Category: functors

Component type: type

Description

Select2nd is a function object that takes a single argument, a pair [1], and returns the pair's second element.

Example

Print all of a map's values.

int main() {
 map<int, double> M;
 M[1] = 0.3;
 M[47] = 0.8;
 M[33] = 0.1;
 transform(M.begin(), M.end(), ostream_iterator<double>(cout, ' '), select2nd<map<int, double>::value_type>());
 // The output is 0.3 0.1 0.8
}

Definition

Defined in the standard header functional, and in the nonstandard backward-compatibility header function.h. This function object is an SGI extension; it is not part of the C++ standard.

Template parameters

Parameter	Description
Pair	The function object's argument type.

Model of

Adaptable Unary Function

Type requirements

There exist some types U and V such that Pair provides the same interface as a pair<U,V>. [1]

Public base classes

unary_function<Pair, Pair::second_type>

Members

Member	Where defined	Description