tolower() not working

Question

The below code snippet is used to convert a string to lower case.

int main()
{
    unsigned char s[] = "AbS.d_";

    tolower(s);
    printf("%s\n", s);

    return 0;
}

I am getting the output as:

AbS.d_

Why the string is not being converted?

Because [tolower()](http://www.cplusplus.com/reference/clibrary/cctype/tolower/) works character-by-character, and returns an *output*. It doesn't convert the whole string at once. And even if it did, it would cause an access violation on your static string ;) — paulsm4, Aug 27 '12 at 16:06
@paulsm4 The string is not static (maybe the question was edited?) — Praetorian, Aug 27 '12 at 16:08
@MatteoItalia, Indeed [it does](http://ideone.com/htlXf). The function takes an `int`, and you pass a pointer. — chris, Aug 27 '12 at 16:11
@chris I see your link and raise you [this one](http://liveworkspace.org/code/21386e9cba33a6b3fe603a3b2d016393). — Luc Danton, Aug 27 '12 at 16:14
@chris: you are right, I tend to forget how forgiving is C in respect to C++. — Matteo Italia, Aug 27 '12 at 16:15
@LucDanton, I agree. Warnings would have maybe saved the OP's question. — chris, Aug 27 '12 at 16:16
@paulsm4: The documentation you cite doesn’t mention a critical point: when you pass a `char` argument, it must be cast to `unsigned char`, not to `int`. See http://pubs.opengroup.org/onlinepubs/9699919799/functions/tolower.html for a better source. — Roland Illig, Jan 03 '15 at 16:06

md5 · Answer 1 · 2012-08-27T16:18:57.783

5

tolower takes a character type as parameter, but you use a string. You need to run through your array, and call tolower for each character.

edited Aug 27 '12 at 16:18

answered Aug 27 '12 at 16:04

md5

7

I think the implementation of `tolower` is guaranteed to be wait-free. – Kerrek SB Aug 27 '12 at 16:08

Rohan · Accepted Answer · 2012-08-27T17:21:52.030

5

tolower takes int and return lowered int.

This should work:

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

edited Aug 27 '12 at 17:21

answered Aug 27 '12 at 16:07

Rohan

Hello infinite loop. Don't you mean `for(i=0; s[i]; i++) { ... }`? – Praetorian Aug 27 '12 at 16:10
Technically it takes an `int`. – chris Aug 27 '12 at 16:13

2 Answers2