Standard Template Library Programmer's Guide

See iterator_category

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

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iterator_category , Iterator Tags, iterator_traits , output_iterator_tag , input_iterator_tag , forward_iterator_tag random_access_iterator_tag

Category: iterators

Component type: type

Random_access_iterator_tag is an empty class: it has no member functions, member variables, or nested types. It is used solely as a "tag": a representation of the Random Access Iterator concept within the C++ type system. Specifically, it is used as a return value for the function iterator_category . Iterator_category takes a single argument, an iterator, and returns an object whose type depends on the iterator's category. Iterator_category 's return value is of type random_access_iterator_tag if its argument is a Random Access Iterator.

See iterator_category.

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

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iterator_category , Iterator Tags, iterator_traits , output_iterator_tag , input_iterator_tag , forward_iterator_tag , bidirectional_iterator_tag

Category: iterators

Component type: type

Input_iterator is an iterator base class: it is intended that an iterator that is a model of Input Iterator, and whose value type and distance type are T and Distance , may be defined by inheriting from input_iterator [1]. Input_iterator is entirely empty: it has no member functions, member variables, or nested types. It exists solely to simplify the definition of the functions iterator_category , distance_type , and value_type .

class my_input_iterator : public input_iterator {

…

};

This declares my_input_iterator to be an Input Iterator whose value type is double and whose distance type is ptrdiff_t . If Iter is an object of class my_input_iterator , then iterator_category(Iter) will return input_iterator_tag() , value_type(Iter) will return (double*)0 , and distance_type(Iter) will return (ptrdiff_t*)0 .

Defined in the standard header iterator, and in the nonstandard backward-compatibility header iterator.h. This class is no longer part of the C++ standard, although it was present in early drafts of the standard. It is retained in this implementation for backward compatibility.

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The distance type must be a signed integral type.

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[1] It is not required that an Input Iterator inherit from the base input_iterator . It is, however, required that the functions iterator_category , distance_type , and value_type be defined for every Input Iterator. (Or, if you are using the iterator_traits mechanism, that iterator_traits is properly specialized for every Input Iterator.) Since those functions are defined for the base input_iterator , the easiest way to ensure that are defined for a new iterator class is to derive that class from input_iterator and rely on the derived-to-base standard conversion of function arguments.

The Iterator Tags overview, iterator_traits , iterator_category , value_type , distance_type , output_iterator , forward_iterator , bidirectional_iterator , random_access_iterator

Category: iterators

Component type: type

Output_iterator is an iterator base class: it is intended that an iterator that is a model of Output Iterator may be defined by inheriting from output_iterator [1]. Output_iterator is entirely empty: it has no member functions, member variables, or nested types. It exists solely to simplify the definition of the functions iterator_category , distance_type , and value_type .

class my_output_iterator : public output_iterator {

…

};

This declares my_output_iterator to be an Output Iterator. If Iter is an object of class my_output_iterator , then iterator_category(Iter) will return output_iterator_tag() , and distance_type and value_type will be undefined for objects of class my_output_iterator .

Defined in the standard header iterator, and in the nonstandard backward-compatibility header iterator.h. This class is no longer part of the C++ standard, although it was present in early drafts of the standard. It is retained in this implementation for backward compatibility.

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