Standard Template Library Programmer's Guide

or 'range of objects'.

[3] The iterator_traits class relies on a C++ feature known as partial specialization. Many of today's compilers don't implement the complete standard; in particular, many compilers do not support partial specialization. If your compiler does not support partial specialization, then you will not be able to use iterator_traits, and you will instead have to continue using the functions iterator_category, distance_type, and value_type.

Concepts

Trivial Iterator

Category: iterators

Component type: concept

Description

A Trivial Iterator is an object that may be dereferenced to refer to some other object. Arithmetic operations (such as increment and comparison) are not guaranteed to be supported.

Refinement of

Assignable, Equality Comparable, Default Constructible

Associated types

Value type

The type of the value obtained by dereferencing a Trivial Iterator

Notation

X A type that is a model of Trivial Iterator

T The value type of X

x, y Object of type X

t Object of type T

Definitions

A type that is a model of Trivial Iterator may be mutable, meaning that the values referred to by objects of that type may be modified, or constant, meaning that they may not. For example, int* is a mutable iterator type and const int* is a constant iterator type. If an iterator type is mutable, this implies that its value type is a model of Assignable; the converse, though, is not necessarily true.

A Trivial Iterator may have a singular value, meaning that the results of most operations, including comparison for equality, are undefined. The only operation that a is guaranteed to be supported is assigning a nonsingular iterator to a singular iterator.

A Trivial Iterator may have a dereferenceable value, meaning that dereferencing it yields a well-defined value. Dereferenceable iterators are always nonsingular, but the converse is not true. For example, a null pointer is nonsingular (there are well defined operations involving null pointers) even thought it is not dereferenceable.

Invalidating a dereferenceable iterator means performing an operation after which the iterator might be nondereferenceable or singular. For example, if p is a pointer, then delete p invalidates p.

Valid expressions

In addition to the expressions defined in Assignable, Equality Comparable, and Default Constructible, the following expressions must be valid.

Name	Expression	Type requirements	Return type
Default constructor	X x
Dereference	*x		Convertible to T [1]
Dereference assignment	*x = t	X is mutable
Member access	x->m[2]	T is a type for which x.m is defined

Expression semantics

Name	Expression	Precondition	Semantics	Postcondition
Default constructor	X x