char_traits

• Summary
• Data Type and Member Function Indexes
• Synopsis
• Description
• Interface
• Types
• Types Default-Values
• Value Functions
• Test Functions
• Conversion Functions
• See Also
• Standards Conformance

A traits class providing types and operations to the basic_string container and iostream classes.

Data Types
char_type int_type off_type pos_type	state_type

Member Functions
assign() compare() copy() eof() eq() eq_int_type() find() length() lt() move()	not_eof() to_char_type() to_int_type()

#include <string>
template<class charT>
struct char_traits

The template structure char_traits<charT> defines the types and functions necessary to implement the iostreams and string template classes. It is templatized on charT, which represents the character container type. Each specialized version of char_traits<charT> provides the default definitions corresponding to the specialized character container type.

Users have to provide specialization for char_traits if they use other character types than char and wchar_t.

template<class charT> 
struct char_traits {

  typedef charT                     char_type;
  typedef INT_T                     int_type;
  typedef POS_T                     pos_type;
  typedef OFF_T                     off_type;
  typedef STATE_T                   state_type;

  static char_type        to_char_type(const int_type&); 
  static int_type         to_int_type(const char_type&);
  static bool             eq(const char_type&,const char_type& );
  static bool             eq_int_type(const int_type&,const int_type&);

  static int_type         eof();
  static int_type         not_eof(const int_type&);

  static void             assign(char_type&,const char_type&);
  static bool             lt(const char_type&,const char_type&);
  static int              compare(const char_type*,const char_type*,size_t);
  static size_t           length(const char_type*);
  static const char_type* find(const char_type*,int n,const char_type&);

  static char_type*       move(char_type*,const char_type*,size_t);
  static char_type*       copy(char_type*,const char_type*, size_t);
  static char_type*       assign(char_type*,size_t,const char_type&);

};

char_type

The type char_type represents the character container type. It must be convertible to int_type.

int_type

The type int_type is another character container type which can also hold an end-of-file value. It is used as the return type of some of the iostream class member functions. If char_type is either char or wchar_t, int_type is int or wint_t, respectively.

off_type

The type off_type represents offsets to positional information. It is used to represent:

• a signed displacement, measured in characters, from a specified position within a sequence.

• an absolute position within a sequence.

The value off_type(-1) can be used as an error indicator. Value of type off_type can be converted to type pos_type, but no validity of the resulting pos_type value is ensured.

If char_type is either char or wchar_t, off_type is streamoff or wstreamoff, respectively.

pos_type

The type pos_type describes an object that can store all the information necessary to restore an arbitrary sequence to a previous stream position and conversion state. The conversion pos_type(off_type(-1)) constructs the invalid pos_type value to signal error.

If char_type is either char or wchar_t, pos_type is streampos or wstreampos, respectively.

state_type

The type state_type holds the conversion state, and is compatible with the function locale::codecvt().

If char_type is either char or wchar_t, state_type is mbstate_t.

void 
assign(char_type& c1, const char_type& c2);

Assigns one character value to another. The value of c2 is assigned to c1.

char_type*
assign(char_type* s,size_t n,const char_type& a);

Assigns one character value to n elements of a character array. The value of a is assigned to n elements of s.

char_type* 
copy(char_type* s1, const char_type* s2, size_t n);

Copies n characters from the object pointed at by s1 into the object pointed at by s2. The ranges of (s1,s1+n) and (s2,s2+n) may not overlap.

int_type 
eof();

Returns an int_type value which represents the end-of-file. It is returned by several functions to indicate end-of-file state, or to indicate an invalid return value.

const char_type* 
find(const char_type* s, int n, const char_type& a);

Looks for the value of a in s. Only n elements of s are examined. Returns a pointer to the matched element if one is found. Otherwise returns a pointer to the n element in s.

size_t 
length(const char_type* s);

Returns the length of a null terminated character string pointed at by s.

char_type* 
move(char_type* s1, const char_type* s2, size_t n);

Moves n characters from the object pointed at by s1 into the object pointed at by s2. The ranges of (s1,s1+n) and (s2,s2+n) may overlap.

int_type 
not_eof(const int_type& c);

Returns a value which is not equal to the end-of-file value.

int 
compare(const char_type* s1,const char_type* s2,size_t n);

Compares n values from s1 with n values from s2. Returns 1 if s1 is greater than s2, -1 if s1 is less than s2, or 0 if they are equal.

bool 
eq(const char_type& c1, const char_type& c2);

Returns true if c1 and c2 represent the same character.

bool 
eq_int_type(const int_type& c1, const int_type& c2);

Returns true if c1 and c2 represents the same character.

bool 
lt(const char_type& c1,const char_type& c2);

Returns true if c1 is less than c2.

char_type 
to_char_type(const int_type& c);

Converts a valid character represented by a value of type int_type to the corresponding char_type value.

int_type 
to_int_type(const char_type& c);

Converts a valid character represented by a value of type char_type to the corresponding int_type value.

iosfwd(3C++), fpos(3C++)

Working Paper for Draft Proposed International Standard for Information Systems--Programming Language C++, Section 21.1.4, 21.1.5, 27.1.2.

ANSI X3J16/ISO WG21 Joint C++ Committee

©Copyright 1996, Rogue Wave Software, Inc.