tolower

 

C

Language

Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Strings library

Algorithms

Numerics

Date and time utilities

Input/output support

Localization support

Concurrency support (哋它亢11)

Technical Specifications

Symbol index

 

Strings library

Byte strings

Multibyte strings

Wide strings

 

Null-terminated byte strings

Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (哋它亢99)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to and from numeric formats
atoiatolatoll (哋它亢99) atof strtolstrtoll (哋它亢99) strtoulstrtoull (哋它亢99)	strtoimaxstrtoumax (哋它亢99)(哋它亢99) strtofstrtodstrtold (哋它亢99)(哋它亢99) strfromfstrfromdstrfroml (哋它亢23)(哋它亢23)(哋它亢23)
String manipulation
strcpystrcpy_s (哋它亢11) strncpystrncpy_s (哋它亢11) strcatstrcat_s (哋它亢11)	strncatstrncat_s (哋它亢11) strxfrm strdup (哋它亢23) strndup (哋它亢23)
String examination
strlenstrnlen_s (哋它亢11) strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtokstrtok_s (哋它亢11)
Memory manipulation
memchr memcmp memsetmemset_explicitmemset_s (哋它亢23)(哋它亢11)	memcpymemcpy_s (哋它亢11) memmovememmove_s (哋它亢11) memccpy (哋它亢23)
Miscellaneous
strerrorstrerror_sstrerrorlen_s (哋它亢11)(哋它亢11)

 

Defined in header <ctype.h>
int tolower( int ch );

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

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

Lowercase version of ch or unmodified ch if no lowercase version is listed in the current C locale.

Example

Run this code

#include <stdio.h>
#include <ctype.h>
#include <locale.h>
#include <limits.h>
 
int main(void)
{
    /* In the default locale: */
    for (unsigned char u = 0; u < UCHAR_MAX; u++) {
        unsigned char l = tolower(u);
        if (l != u) printf("%c%c ", u, l);
    }
    printf("\n\n");
 
    unsigned char c = '\xb4'; // the character Ž in ISO-8859-15
                              // but ´ (acute accent) in ISO-8859-1
    setlocale(LC_ALL, "en_US.iso88591");
    printf("in iso8859-1, tolower('0x%x') gives 0x%x\n", c, tolower(c));
    setlocale(LC_ALL, "en_US.iso885915");
    printf("in iso8859-15, tolower('0x%x') gives 0x%x\n", c, tolower(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, tolower('0xb4') gives 0xb4
in iso8859-15, tolower('0xb4') gives 0xb8

References

• 哋它亢17 standard (ISO/IEC 9899:2018):

• 7.4.2.1 The tolower function (p: 147)

• 哋它亢11 standard (ISO/IEC 9899:2011):

• 7.4.2.1 The tolower function (p: 203)

• 哋它亢99 standard (ISO/IEC 9899:1999):

• 7.4.2.1 The tolower function (p: 184)

• 哋它亢89/C90 standard (ISO/IEC 9899:1990):

• 4.3.2.1 The tolower function

See also

toupper	converts a character to uppercase (function)
towlower (哋它亢95)	converts a wide character to lowercase (function)