isupper

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< c ‎ | string ‎ | byte
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(C11) (C11)
Defined in header <ctype.h>
int isupper ( int ch ) ;

Checks if the given character is an uppercase character according to the current C locale. In the default "C" locale, isupper returns true only for the uppercase letters ( ABCDEFGHIJKLMNOPQRSTUVWXYZ ).

If isupper returns true , it is guaranteed that iscntrl , isdigit , ispunct , and isspace return false for the same character in the same C locale.

The behavior is undefined if the value of ch is not representable as unsigned char and is not equal to EOF .

Parameters

ch - character to classify

Return value

Non-zero value if the character is an uppercase letter, zero otherwise.

Example

Run this code 
#include <stdio.h>
#include <ctype.h>
#include <locale.h>
 
int main(void)
{
    unsigned char c = '\xc6'; // letter Æ in ISO-8859-1
    printf("In the default C locale, \\xc6 is %suppercase\n",
           isupper(c) ? "" : "not " );
    setlocale(LC_ALL, "en_GB.iso88591");
    printf("In ISO-8859-1 locale, \\xc6 is %suppercase\n",
           isupper(c) ? "" : "not " );
}

Possible output: 

In the default C locale, \xc6 is not uppercase
In ISO-8859-1 locale, \xc6 is uppercase

References

  • C17 standard (ISO/IEC 9899:2018):
  • 7.4.1.11 The isupper function (p: 147)
  • C11 standard (ISO/IEC 9899:2011):
  • 7.4.1.11 The isupper function (p: 203)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.4.1.11 The isupper function (p: 184)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • 4.3.1.10 The isupper function

See also

(C95)
checks if a wide character is an uppercase character
(function)
C++ documentation for isupper
ASCII values characters

iscntrl
iswcntrl

isprint
iswprint

isspace
iswspace

isblank
iswblank

isgraph
iswgraph

ispunct
iswpunct

isalnum
iswalnum

isalpha
iswalpha

isupper
iswupper

islower
iswlower

isdigit
iswdigit

isxdigit
iswxdigit

decimal hexadecimal octal
0–8 \x0 – \x8 \0 – \10 control codes ( NUL , etc.) ≠0 0 0 0 0 0 0 0 0 0 0 0
9 \x9 \11 tab ( \t ) ≠0 0 ≠0 ≠0 0 0 0 0 0 0 0 0
10–13 \xA – \xD \12 – \15 whitespaces ( \n , \v , \f , \r ) ≠0 0 ≠0 0 0 0 0 0 0 0 0 0
14–31 \xE – \x1F \16 – \37 control codes ≠0 0 0 0 0 0 0 0 0 0 0 0
32 \x20 \40 space 0 ≠0 ≠0 ≠0 0 0 0 0 0 0 0 0
33–47 \x21 – \x2F \41 – \57 !"#$%&'()*+,-./ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
48–57 \x30 – \x39 \60 – \71 0123456789 0 ≠0 0 0 ≠0 0 ≠0 0 0 0 ≠0 ≠0
58–64 \x3A – \x40 \72 – \100 :;<=>?@ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
65–70 \x41 – \x46 \101 – \106 ABCDEF 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 ≠0
71–90 \x47 – \x5A \107 – \132 GHIJKLMNOP
QRSTUVWXYZ 		0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 0
91–96 \x5B – \x60 \133 – \140 [\]^_` 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
97–102 \x61 – \x66 \141 – \146 abcdef 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 ≠0
103–122 \x67 – \x7A \147 – \172 ghijklmnop
qrstuvwxyz 		0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 0
123–126 \x7B – \x7E \173 – \176 {|}~ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
127 \x7F \177 backspace character ( DEL ) ≠0 0 0 0 0 0 0 0 0 0 0 0
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