From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/c/language%2Fcharacter_constant.html | 106 +++++++++++++++++++++++++++ 1 file changed, 106 insertions(+) create mode 100644 devdocs/c/language%2Fcharacter_constant.html (limited to 'devdocs/c/language%2Fcharacter_constant.html') diff --git a/devdocs/c/language%2Fcharacter_constant.html b/devdocs/c/language%2Fcharacter_constant.html new file mode 100644 index 00000000..acf4a443 --- /dev/null +++ b/devdocs/c/language%2Fcharacter_constant.html @@ -0,0 +1,106 @@ +

Character constant

Syntax

+ + + + + + + + + +
'c-char ' (1)
u8'c-char ' (2) (since C23)
u'c-char ' (3) (since C11)
U'c-char ' (4) (since C11)
L'c-char ' (5)
'c-char-sequence ' (6)
L'c-char-sequence ' (7)
u'c-char-sequence ' (8) (since C11)(removed in C23)
U'c-char-sequence ' (9) (since C11)(removed in C23)

where

+ + +
(since C99)
+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) UTF-8 character constant, e.g. u8'a'. Such constant has type char8_t and the value equal to ISO 10646 code point value of c-char, provided that the code point value is representable with a single UTF-8 code unit (that is, c-char is in the range 0x0-0x7F, inclusive). If c-char is not representable with a single UTF-8 code unit, the program is ill-formed.
+ + + +
3) 16-bit wide character constant, e.g. u'่ฒ“', but not u'๐ŸŒ' (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 value is implementation-defined. 4) 32-bit wide character constant, e.g. U'่ฒ“' or U'๐ŸŒ'. 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 value is implementation-defined. (until C23)
3) UTF-16 character constant, e.g. u'่ฒ“', but not u'๐ŸŒ' (u'\U0001f34c'). Such constant has type char16_t and the value equal to ISO 10646 code point value of c-char, provided that the code point value is representable with a single UTF-16 code unit (that is, c-char is in the range 0x0-0xD7FF or 0xE000-0xFFFF, inclusive). If c-char is not representable with a single UTF-16 code unit, the program is ill-formed. 4) UTF-32 character constant, e.g. U'่ฒ“' or U'๐ŸŒ'. Such constant has type char32_t and the value equal to ISO 10646 code point value of c-char, provided that the code point value is representable with a single UTF-32 code unit (that is, c-char is in the range 0x0-0xD7FF or 0xE000-0x10FFFF, inclusive). If c-char is not representable with a single UTF-32 code unit, the program is ill-formed. (since C23)
+5) wide character constant, e.g. L'ฮฒ' or L'่ฒ“. 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 value is implementation-defined .
+6) multicharacter constant, e.g. 'AB', has type int and implementation-defined value.
+7) wide multicharacter constant, e.g. L'AB', has type wchar_t and implementation-defined value.
+8) 16-bit multicharacter constant, e.g. u'CD', has type char16_t and implementation-defined value.
+9) 32-bit multicharacter constant, e.g. U'XY', has type char32_t and implementation-defined value.

Notes

Multicharacter constants were inherited by C from the B programming language. Although not specified by the C standard, most compilers (MSVC is a notable exception) 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++, encodable ordinary character literals 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.

+

16/32-bit multicharacter constants are not widely supported and removed in C23. Some common implementations (e.g. clang) do not accept them at all.

+

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':\t %#010x\n", c1);
+    int c2='๐ŸŒ'; printf("'๐ŸŒ':\t %#010x\n\n", c2); // implementation-defined
+ 
+    // multicharacter constant
+    int c3='ab'; printf("'ab':\t %#010x\n\n", c3); // implementation-defined
+ 
+    // 16-bit wide character constants
+    char16_t uc1 = u'a'; printf("'a':\t %#010x\n", (int)uc1);
+    char16_t uc2 = u'ยข'; printf("'ยข':\t %#010x\n", (int)uc2);
+    char16_t uc3 = u'็Œซ'; printf("'็Œซ':\t %#010x\n", (int)uc3);
+    // implementation-defined (๐ŸŒ maps to two 16-bit characters)
+    char16_t uc4 = u'๐ŸŒ'; printf("'๐ŸŒ':\t %#010x\n\n", (int)uc4);
+ 
+    // 32-bit wide character constants
+    char32_t Uc1 = U'a'; printf("'a':\t %#010x\n", (int)Uc1);
+    char32_t Uc2 = U'ยข'; printf("'ยข':\t %#010x\n", (int)Uc2);
+    char32_t Uc3 = U'็Œซ'; printf("'็Œซ':\t %#010x\n", (int)Uc3);
+    char32_t Uc4 = U'๐ŸŒ'; printf("'๐ŸŒ':\t %#010x\n\n", (int)Uc4);
+ 
+    // wide character constants
+    wchar_t wc1 = L'a'; printf("'a':\t %#010x\n", (int)wc1);
+    wchar_t wc2 = L'ยข'; printf("'ยข':\t %#010x\n", (int)wc2);
+    wchar_t wc3 = L'็Œซ'; printf("'็Œซ':\t %#010x\n", (int)wc3);
+    wchar_t wc4 = L'๐ŸŒ'; printf("'๐ŸŒ':\t %#010x\n\n", (int)wc4);
+}

Possible output:

+
constant value     
+-------- ----------
+'a':         0x00000061
+'๐ŸŒ':         0xf09f8d8c
+ 
+'ab':         0x00006162
+ 
+'a':         0x00000061
+'ยข':         0x000000a2
+'็Œซ':         0x0000732b
+'๐ŸŒ':         0x0000df4c
+ 
+'a':         0x00000061
+'ยข':         0x000000a2
+'็Œซ':         0x0000732b
+'๐ŸŒ':         0x0001f34c
+ 
+'a':         0x00000061
+'ยข':         0x000000a2
+'็Œซ':         0x0000732b
+'๐ŸŒ':         0x0001f34c

References

See also

+
C++ documentation for Character literal
+

+ © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
+ https://en.cppreference.com/w/c/language/character_constant +

+
-- cgit v1.2.3