View source for c/string/byte/isupper

{{c/title|isupper}}
{{c/string/byte/navbar}}
{{ddcl | 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, {{tt|isupper}} returns true only for the uppercase letters ({{tt|ABCDEFGHIJKLMNOPQRSTUVWXYZ}}).

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

The behavior is undefined if the value of {{tt|ch}} is not representable as {{c|unsigned char}} and is not equal to {{c|EOF}}.

===Parameters===
{{par begin}}
{{par | ch | character to classify}}
{{par end}}

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

===Example===
{{example
 | 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 " );
}
 | p=true
 | output=
In the default C locale, \xc6 is not uppercase
In ISO-8859-1 locale, \xc6 is uppercase
}}

===References===
{{ref std c17}}
{{ref std | section=7.4.1.11 | title=The isupper function | p=147}}
{{ref std end}}
{{ref std c11}}
{{ref std | section=7.4.1.11 | title=The isupper function | p=203}}
{{ref std end}}
{{ref std c99}}
{{ref std | section=7.4.1.11 | title=The isupper function | p=184}}
{{ref std end}}
{{ref std c89}}
{{ref std | section=4.3.1.10 | title=The isupper function}}
{{ref std end}}

===See also===
{{dsc begin}}
{{dsc inc | c/string/wide/dsc iswupper}}
{{dsc see cpp | cpp/string/byte/isupper}}
{{dsc end}}

{{c/string/character classes}}

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