Standard Template Library Programmer's Guide

As with many other adaptors, it is usually inconvenient to use mem_fun1_ref_t 's constructor directly. It is usually better to use the helper function mem_fun_ref [2] instead.

Given a vector of vectors, extract one element from each vector.

int main() {

int A1[5] = {1, 2, 3, 4, 5};

int A2[5] = {1, 1, 2, 3, 5};

int A3[5] = {1, 4, 1, 5, 9};

vector > V;

V.push_back(vector(A1, A1 + 5));

V.push_back(vector(A2, A2 + 5));

V.push_back(vector(A3, A3 + 5));

int indices[3] = {0, 2, 4};

int& (vector::*extract)(vector::size_type);

extract = vector::operator[];

transform (V.begin(), V.end(), indices, ostream_iterator(cout, "\n"), mem_fun_ref(extract));

}

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

Adaptable Binary Function

X has at least one member function that takes a single argument of type Arg and that returns a value of type Result . [1]

binary_function

These members are not defined in the Adaptable Binary Function requirements, but are specific to mem_fun1_ref_t .

[1] The type Result is permitted to be void . That is, this adaptor may be used for functions that return no value. However, this presents implementation difficulties. According to the draft C++ standard, it is possible to return from a void function by writing return void instead of just return . At present, however (early 1998), very few compilers support that feature. As a substitute, then, mem_fun1_ref_t uses partial specialization to support void member functions. If your compiler has not implemented partial specialization, then you will not be able to use mem_fun1_ref_t with member functions whose return type is void .

[2] This helper function was called mem_fun1_ref in drafts of the C++ standard, but it is called mem_fun_ref in the final standard. This implementation provides both versions for backward compatibility, but mem_fun1_ref will be removed in a future release.

mem_fun_t , mem_fun_ref_t , mem_fun1_t

Category: utilities

Component type: concept

A type is Assignable if it is possible to copy objects of that type and to assign values to variables.

XA type that is a model of Assignable

x, y Object of type X

• int

[1] One implication of this requirement is that a const type is not Assignable. For example, const int is not Assignable: if x is declared to be of type const int , then x = 7 is illegal. Similarly, the type pair is not Assignable.

[2] The reason this says " x is a copy of y ", rather than " x == y ", is that operator== is not necessarily defined: equality is not a requirement of Assignable. If the type X is EqualityComparable as well as Assignable, then a copy of x should compare equal to x .

DefaultConstructible

Category: utilities

Component type: concept

A type is DefaultConstructible if it has a default constructor, that is, if it is possible to construct an object of that type without initializing the object to any particular value.

XA type that is a model of DefaultConstructible