to Functions
Each of the to functions and its associated macro, if any, converts a single character to another character.
|
Remarks
The to functions and macro conversions are as follows.
Routine |
Macro |
Description |
|---|---|---|
__toascii |
__toascii |
Converts c to ASCII character |
tolower |
tolower |
Converts c to lowercase if appropriate |
_tolower |
_tolower |
Converts c to lowercase |
towlower |
None |
Converts c to corresponding wide-character lowercase letter |
toupper |
toupper |
Converts c to uppercase if appropriate |
_toupper |
_toupper |
Converts c to uppercase |
towupper |
None |
Converts c to corresponding wide-character uppercase letter |
To use the function versions of the to routines that are also defined as macros, either remove the macro definitions with #undef directives or do not include CTYPE.H. If you use the /Za compiler option, the compiler uses the function version of toupper or tolower. Declarations of the toupper and tolower functions are in STDLIB.H.
The __toascii routine sets all but the low-order 7 bits of c to 0, so that the converted value represents a character in the ASCII character set. If c already represents an ASCII character, c is unchanged.
The tolower and toupper routines:
Are dependent on the LC_CTYPE category of the current locale (tolower calls isupper and toupper calls islower).
Convert c if c represents a convertible letter of the appropriate case in the current locale and the opposite case exists for that locale. Otherwise, c is unchanged.
The _tolower and _toupper routines:
Are locale-independent, much faster versions of tolower and toupper.
Can be used only when isascii(c) and either isupper(c) or islower(c), respectively, are nonzero.
Have undefined results if c is not an ASCII letter of the appropriate case for converting.
The towlower and towupper functions return a converted copy of c if and only if both of the following conditions are nonzero. Otherwise, c is unchanged.
c is a wide character of the appropriate case (that is, for which iswupper or iswlower, respectively, is nonzero).
There is a corresponding wide character of the target case (that is, for which iswlower or iswupper, respectively, is nonzero).
Example
// crt_toupper.c
/* This program uses toupper and tolower to
* analyze all characters between 0x0 and 0x7F. It also
* applies _toupper and _tolower to any code in this
* range for which these functions make sense.
*/
#include <ctype.h>
#include <string.h>
char msg[] = "Some of THESE letters are Capitals.";
char *p;
int main( void )
{
printf( "%s\n", msg );
/* Reverse case of message. */
for( p = msg; p < msg + strlen( msg ); p++ )
{
if( islower( *p ) )
putchar( _toupper( *p ) );
else if( isupper( *p ) )
putchar( _tolower( *p ) );
else
putchar( *p );
}
}
Some of THESE letters are Capitals. sOME OF these LETTERS ARE cAPITALS.