character constant

character constant

Syntax

' c-char '	(1)
u ' c-char ' (since C11)	(2)
U ' c-char ' (since C11)	(3)
L ' c-char '	(4)
' c-char-sequence '	(5)

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

Multicharacter constants were inherited by C from the B programming language. Although not specified by the C standard, compilers implement multicharacter constants as specified in B: the values of each char in the constant initialize successive bytes of the resulting integer, in big-endian zero-padded right-adjusted order, e.g. the value of '\1' is 0x00000001 and 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

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