toupper

 

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isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
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atoiatolatoll (C99) atof strtolstrtoll (C99) strtoulstrtoull (C99)	strtoimaxstrtoumax (C99)(C99) strtofstrtodstrtold (C99)(C99) strfromfstrfromdstrfroml (C23)(C23)(C23)
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Defined in header <ctype.h>
int toupper( int ch );

Converts the given character to uppercase according to the character conversion rules defined by the currently installed C locale.

In the default "C" locale, the following lowercase letters abcdefghijklmnopqrstuvwxyz are replaced with respective uppercase letters ABCDEFGHIJKLMNOPQRSTUVWXYZ.

Parameters

ch

-

character to be converted. If the value of ch is not representable as unsigned char and does not equal EOF, the behavior is undefined.

Return value

Uppercase version of ch or unmodified ch if no uppercase version is listed in the current C locale.

Example

Run this code

#include <ctype.h>
#include <limits.h>
#include <locale.h>
#include <stdio.h>
 
int main(void)
{
    // in the default locale:
    for (unsigned char l = 0, u; l != UCHAR_MAX; ++l)
        if ((u = toupper(l)) != l)
            printf("%c%c ", l, u);
    printf("\n\n");
 
    unsigned char c = '\xb8'; // the character ž in ISO-8859-15
                              // but ¸ (cedilla) in ISO-8859-1
    setlocale(LC_ALL, "en_US.iso88591");
    printf("in iso8859-1, toupper('0x%x') gives 0x%x\n", c, toupper(c));
    setlocale(LC_ALL, "en_US.iso885915");
    printf("in iso8859-15, toupper('0x%x') gives 0x%x\n", c, toupper(c));
}

Possible output:

aA bB cC dD eE fF gG hH iI jJ kK lL mM nN oO pP qQ rR sS tT uU vV wW xX yY zZ
 
in iso8859-1, toupper('0xb8') gives 0xb8
in iso8859-15, toupper('0xb8') gives 0xb4

References

• C23 standard (ISO/IEC 9899:2024):

• 7.4.2.2 The toupper function (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• 7.4.2.2 The toupper function (p: 147-148)

• C11 standard (ISO/IEC 9899:2011):

• 7.4.2.2 The toupper function (p: 204)

• C99 standard (ISO/IEC 9899:1999):

• 7.4.2.2 The toupper function (p: 185)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.3.2.2 The toupper function

See also

tolower	converts a character to lowercase (function)
towupper (C95)	converts a wide character to uppercase (function)
C++ documentation for toupper