character constant

Syntax

where.

• c-char is either
• a character from the basic source character set minus single-quote ('), backslash (\), or the newline character.
• escape sequence: one of special character escapes \' \" \? \\ \a \b \f \n \r \t \v, hex escapes \x... or octal escapes \... as defined in escape sequences.

• universal character name, \u... or \U... as defined in escape sequences.

  (since C99)

  • c-char-sequence is a sequence of two or more c-chars.
  1) single-byte integer character constant, e.g. 'a' or '\n' or '\13'. Such constant has type int and a value equal to the representation of c-char in the execution character set as a value of type char mapped to int. If c-char is not representable as a single byte in the execution character set, the value is implementation-defined.
  2) 16-bit wide character constant, e.g. u'貓', but not u'🍌' (u'\U0001f34c'). Such constant has type char16_t and a value equal to the value of c-char in the 16-bit encoding produced by mbrtoc16 (normally UTF-16). If c-char is not representable or maps to more than one 16-bit character, the behavior is implementation-defined.
  3) 32-bit wide character constant, e.g. U'貓' or U'🍌'. Such constant has type char32_t and a value equal to the value of c-char in in the 32-bit encoding produced by mbrtoc32 (normally UTF-32). If c-char is not representable or maps to more than one 32-bit character, the behavior is implementation-defined.
  4) wide character constant, e.g. L'β' or L'貓. Such constant has type wchar_t and a value equal to the value of c-char in the execution wide character set (that is, the value that would be produced by mbtowc). If c-char is not representable or maps to more than one wide character (e.g. a non-BMP value on Windows where wchar_t is 16-bit), the behavior is implementation-defined .
  5) multicharacter constant, e.g. 'AB', has type int and implementation-defined value.

  Notes

  Many implementations of multicharacter constants use the values of each char in the constant to initialize successive bytes of the resulting integer, in big-endian order, e.g. the value of '\1\2\3\4' is 0x01020304.

  In C++, ordinary character constants have type char, rather than int.

  Unlike integer constants, a character constant may have a negative value if char is signed: on such implementations '\xFF' is an int with the value -1.

  When used in a controlling expression of #if or #elif, character constants may be interpreted in terms of the source character set, the execution character set, or some other implementation-defined character set.

  Example

  #include <stddef.h>
  #include <stdio.h>
  #include <uchar.h>
   
  int main (void)
  {
      printf("constant    value     \n");
      printf("--------    ----------\n");
   
      // integer character constants,
      int c1='a'; printf("'a':        %#010x\n", c1);
      int c2='🍌'; printf("'🍌':       %#010x\n\n", c2); // implementation-defined
   
      // multicharacter constant
      int c3='ab'; printf("'ab':       %#010x\n\n", c3); // implementation-defined
   
      // 16-bit wide character constants
      char16_t uc1 = u'a'; printf("'a':        %#010x\n", (int)uc1);
      char16_t uc2 = u'¢'; printf("'¢':        %#010x\n", (int)uc2);
      char16_t uc3 = u'猫'; printf("'猫':       %#010x\n", (int)uc3);
      // implementation-defined (🍌 maps to two 16-bit characters)
      char16_t uc4 = u'🍌'; printf("'🍌':       %#010x\n\n", (int)uc4);
   
      // 32-bit wide character constants
      char32_t Uc1 = U'a'; printf("'a':        %#010x\n", (int)Uc1);
      char32_t Uc2 = U'¢'; printf("'¢':        %#010x\n", (int)Uc2);
      char32_t Uc3 = U'猫'; printf("'猫':       %#010x\n", (int)Uc3);
      char32_t Uc4 = U'🍌'; printf("'🍌':       %#010x\n\n", (int)Uc4);
   
      // wide character constants
      wchar_t wc1 = L'a'; printf("'a':        %#010x\n", (int)wc1);
      wchar_t wc2 = L'¢'; printf("'¢':        %#010x\n", (int)wc2);
      wchar_t wc3 = L'猫'; printf("'猫':       %#010x\n", (int)wc3);
      wchar_t wc4 = L'🍌'; printf("'🍌':       %#010x\n\n", (int)wc4);
  }

  Possible output:

  constant    value     
  --------    ----------
  'a':        0x00000061
  '🍌':       0xf09f8d8c
   
  'ab':       0x00006162
   
  'a':        0x00000061
  '¢':        0x000000a2
  '猫':       0x0000732b
  '🍌':       0x0000df4c
   
  'a':        0x00000061
  '¢':        0x000000a2
  '猫':       0x0000732b
  '🍌':       0x0001f34c
   
  'a':        0x00000061
  '¢':        0x000000a2
  '猫':       0x0000732b
  '🍌':       0x0001f34c

  References

  • C11 standard (ISO/IEC 9899:2011):
  • 6.4.4.4 Character constants (p: 67-70)
  • C99 standard (ISO/IEC 9899:1999):
  • 6.4.4.4 Character constants (p: 59-61)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • 3.1.3.4 Character constants

  See also

  C++ documentation for character literal