How do I lowercase a string in C? [closed]

Question

How can I convert a mixed case string to a lowercase string in C?

Answer 1

It's in the standard library, and that's the most straight forward way I can see to implement such a function. So yes, just loop through the string and convert each character to lowercase.

Something trivial like this:

#include <ctype.h>

for(int i = 0; str[i]; i++){
  str[i] = tolower(str[i]);
}

or if you prefer one liners, then you can use this one by J.F. Sebastian:

for ( ; *p; ++p) *p = tolower(*p);

Answer 2

to convert to lower case is equivalent to rise bit 0x60:

for(char *p = pstr;*p;++p) *p=*p>0x40&&*p<0x5b?*p|0x60:*p;

(for latin codepage of course)

Answer 3

Are you just dealing with ASCII strings, and have no locale issues? Then yes, that would be a good way to do it.

Answer 4

If you need Unicode support in the lower case function see this question: Light C Unicode Library

Answer 5

If we're going to be as sloppy as to use tolower(), do this:

char blah[] = "blah blah Blah BLAH blAH\0"; int i=0; while(blah[i]|=' ', blah[++i]) {}

But, well, it kinda explodes if you feed it some symbols/numerals, and in general it's evil. Good interview question, though.