character constant

C

Language

Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Atomic operations (C11)

Thread support (C11)

Technical Specifications

C language

ASCII chart

Basic concepts

Keywords

Preprocessor

Statements

Expressions

Initialization

Declarations

Functions

Miscellaneous

history of C

Technical Specifications

Expressions

General

value category

evaluation order and sequence points

constant expressions

implicit conversions

generic selection (C11)

constants and literals

integer constant

floating constant

character constant

string literal

compound literal (C99)

operators

operator precedence

member access and indirection

logical operators

comparison operators

arithmetic operators

assignment operators

increment and decrement

function call, comma, conditional operator

sizeof

alignof (C11)

cast operators

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'', 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'' 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'' or L'. 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

Run this code

#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''; printf("'':      %#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''; printf("'':      %#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''; printf("'':      %#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
'':       0x0000732b
'':       0x0000df4c

'a':        0x00000061
'':        0x000000a2
'':       0x0000732b
'':       0x0001f34c

'a':        0x00000061
'':        0x000000a2
'':       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