Standard Template Library Programmer's Guide

All other operations are constant time.

• char_traits

• char_traits

string

Category: utilities

Component type: type

The char_traits class is the default Character Traits class used by the library; it is the only predefined Character Traits class.

The char_traits class is of no use by itself. It is used as a template parameter of other classes, such as the basic_string template.

Defined in the standard header string.

Character Traits

charT is either char or wchar_t .

(All of char_traits 's member functions are defined for arbitrary types, but some of char_traits 's members must be explicitly specialized if char_traits is to be useful for other types than char and wchar_t .)

None.

All of char_traits 's members are static. There is never any reason to create an object of type char_traits .

None. All of char_traits 's members are defined in the Character Traits requirements.

Character Traits, string

Category: containers

Component type: type

The basic_string class represents a Sequence of characters. It contains all the usual operations of a Sequence, and, additionally, it contains standard string operations such as search and concatenation.

The basic_string class is parameterized by character type, and by that type's Character Traits. Most of the time, however, there is no need to use the basic_string template directly. The types string and wstring are typedefs for, respectively, basic_string and basic_string .

Some of basic_string 's member functions use an unusual method of specifying positions and ranges. In addition to the conventional method using iterators, many of basic_string 's member functions use a single value pos of type size_type to represent a position (in which case the position is begin() + pos , and many of basic_string 's member functions use two values, pos and n , to represent a range. In that case pos is the beginning of the range and n is its size. That is, the range is [begin() + pos, begin() + pos + n) .

Note that the C++ standard does not specify the complexity of basic_string operations. In this implementation, basic_string has performance characteristics very similar to those of vector : access to a single character is O(1 ), while copy and concatenation are O(N ). By contrast, rope has very different performance characteristics: most rope operations have logarithmic complexity.

Note also that, according to the C++ standard, basic_string has very unusual iterator invalidation semantics. Iterators may be invalidated by swap , reserve , insert , and erase (and by functions that are equivalent to insert and/or erase , such as clear , resize , append , and replace ). Additionally, however, the first call to any non-const member function, including the non-const version of begin() or operator[] , may invalidate iterators. (The intent of these iterator invalidation rules is to give implementors greater freedom in implementation techniques.) In this implementation, begin() , end() , rbegin() , rend() , operator[] , c_str() , and data() do not invalidate iterators. In this implementation, iterators are only invalidated by member functions that explicitly change the string's contents.