Standard Template Library Programmer's Guide

binary_function

All of project1st 's members are defined in the Adaptable Binary Function requirements. project1st does not introduce any new members.

Function objects, identity , project2nd , select1st , select2nd

Category: functors

Component type: type

Project2nd is a function object that takes two arguments and returns its second argument; the first argument is unused. It is essentially a generalization of identity to the case of a Binary Function.

int main() {

vector v1(10, (char*) 0);

vector v2(10, 137);

vector result(10);

transform(v1.begin(), v1.end(), v2.begin(), result.begin(), project2nd());

assert(equal(v2.begin(), v2.end(), result.begin()));

}

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.

Adaptable Binary Function

None.

binary_function

All of project2nd 's members are defined in the Adaptable Binary Function requirements. project2nd does not introduce any new members.

Function objects, identity , project1st , select1st , select2nd

Category: functors

Component type: type

Select1st is a function object that takes a single argument, a pair [1], and returns the pair's first element.

Print all of a map 's keys.

int main() {

map M;

M[1] = 0.3;

M[47] = 0.8;

M[33] = 0.1;

transform(M.begin(), M.end(), ostream_iterator(cout, " "), select1st::value_type>());

// The output is 1 33 47.

}

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.

Adaptable Unary Function

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

unary_function

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

[1] Pair is not actually required to be a pair , 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 .

identity , select2nd , project1st , project2nd

Category: functors

Component type: type

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

Print all of a map 's values.

int main() {

map M;

M[1] = 0.3;

M[47] = 0.8;

M[33] = 0.1;

transform(M.begin(), M.end(), ostream_iterator(cout, " "), select2nd::value_type>());

// The output is 0.3 0.1 0.8

}

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.

Adaptable Unary Function