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Apache C++ Standard Library Reference Guide

Forward Iterators

Library:  Iterators

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A forward-moving iterator that can both read and write


NOTE -- For a complete discussion of iterators, see the Iterators section of this reference.

Iterators are a generalization of pointers that allow a C++ program to uniformly interact with different data structures. Forward iterators are forward moving, and have the ability to both read and write data. These iterators satisfy the requirements listed below.

Key to Iterator Requirements

The following key pertains to the iterator requirements listed below:

a and b

values of type X


value representing a distance between two iterators

u, Distance, tmp and m



value of type X&


value of type T

Requirements for Forward Iterators

The following expressions must be valid for forward iterators:

X u

u might have a singular value


X() might be singular


copy constructor, a == X(a)

X u(a)

copy constructor, u == a

X u = a

assignment, u == a

a == b, a != b

return value convertible to bool


return value convertible to T&


equivalent to (*a).m


returns X&


return value convertible to const X&


returns T&

Forward iterators have the condition that a == b implies *a == *b.

There are no restrictions on the number of passes an algorithm may make through the structure.

See Also

Iterators, Bidirectional Iterators

Standards Conformance

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 24.1.3

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