< c‎ | string‎ | byte
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.


[edit] 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.

[edit] Return value

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

[edit] Example

#include <stdio.h>
#include <ctype.h>
#include <locale.h>
#include <limits.h>
int main(void)
    /* In the default locale: */
    unsigned char l;
    for (unsigned char u=0; u<UCHAR_MAX; u++) {
        l = tolower(u);
        if (l!=u) printf("%c%c ", u,l);
    unsigned char c = '\xb4'; // the character Ž in ISO-8859-15
                              // but ´ (acute accent) in ISO-8859-1 
    unsigned char c2 = c;   // for printing
    setlocale(LC_ALL, "en_US.iso88591");
    printf("in iso8859-1, tolower('0x%x') gives 0x%x\n", c2, tolower(c));
    setlocale(LC_ALL, "en_US.iso885915");
    printf("in iso8859-15, tolower('0x%x') gives 0x%x\n", c2, tolower(c));


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

[edit] References

  • C11 standard (ISO/IEC 9899:2011):
  • The tolower function (p: 203)
  • C99 standard (ISO/IEC 9899:1999):
  • The tolower function (p: 184)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • The tolower function

[edit] See also

converts a character to uppercase
converts a wide character to lowercase
C++ documentation for tolower