Standard Template Library Programmer's Guide

binary_function

All of logical_or 's members are defined in the Adaptable Binary Function and Default Constructible requirements. Logical_or does not introduce any new members.

[1] Logical_and and logical_or are not very useful by themselves. They are mainly useful because, when combined with the function object adaptor binary_compose , they perform logical operations on other function objects.

The function object overview, logical_and , logical_not .

Category: functors

Component type: type

Logical_not is a function object; specifically, it is an Adaptable Predicate, which means it is a function object that tests the truth or falsehood of some condition. If f is an object of class logical_not and x is an object of class T (where T is convertible to bool ) then f(x) returns true if and only if x is false .

Transforms a vector of bool into its logical complement.

vector V;

…

transform(V.begin(), V.end(), V.begin(), logical_not());

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

Adaptable Predicate, DefaultConstructible

T must be convertible to bool .

unary_function

The function object overview, logical_or , logical_and .

Category: functors

Component type: type

Identity is a Unary Function that represents the identity function: it takes a single argument x , and returns x .

int main() {

int x = 137;

identity id;

assert(x == id(x));

}

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

Adaptable Unary Function

None.

unary_function

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

[1] It is essential that the return type and the argument type are the same: generalizing identity to allow them to differ would not work. The reason is that identity returns a const reference to its argument, rather than a copy of its argument. If identity were allowed to perform a conversion, then this would be a dangling reference.

The function object overview, select1st , select2nd , project1st , project2nd

Category: functors

Component type: type

Project1st is a function object that takes two arguments and returns its first argument; the second argument is unused. It is essentially a generalization of identity to the case of a Binary Function.

int main() {

vector v1(10, 137);

vector v2(10, (char*) 0);

vector result(10);

transform(v1.begin(), v1.end(), v2.begin(), result.begin(), project1st());

assert(equal(v1.begin(), v1.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.