How to fix "chown: invalid group:" if the user does not exist on the running system?

Question

Following code is supposed to return the upper case string of the source. It works but does not convert the string. Could not figure out what was wrong.

char *StrUpper (char *s) {
    int i = 0;
    char *t = &s [i];
    while (*t) {
        if ((*t > 0x5a) && (*t < 0x7b)) t = (t - 32);
        t = &s [i++];
    }
    return (s);
}

int main () {
    printf ("%s\n", StrUpper ("lower case string"));
    return (0);
}

Solution

Use the numerical UID/GID instead of the user/group name.

You can find the UID/GID on the system the disk belongs to by using

  id some_username

or

ls -ln some_file

where some_file is a file that belongs to user you are looking for

Comments

[davmac]

'it works but does not convert the string' - surely this means it doesn't work?

[Rahul Tripathi]

Also to add that the reason why you say that it works is because you are getting an undefined behavior.

[Unn]

It might be good to mention that you're looking at the 0th element twice: t = &s [i++] might want to be replaced with t = &s [++i]

[José Manuel Blasco]

In my case, I was using chown with $USER:(id -n $USER) that fills the group. But the group had whitespaces so I had to surround the group part. $USER:"(id -n $USER)" worked for me

[ssd]

I've already tried that (*t = *t - 32) thing; in that case however, codeblock crashes like: Problem signature: Problem Event Name: APPCRASH ... Exception Code: c0000005

[ssd]

Just tried your code above, codeblocks crashes like: Problem Event Name: APPCRASH Exception Code: c0000005

[Vlad from Moscow]

@merkez3110 The problem is not with the function I showed. The problem with how you call it. For example you may not use string literals as arguments of the function.

[ssd]

I've already tried the code below, no change: ` int main () { char *s = "lower case string"; printf ("%s\n", StrUpper (s)); return (0); }`

[Some programmer dude]

@merkez3110 That's because s still points to the constant string literal. Instead do char s[] = "...";

[Vlad from Moscow]

@@merkez3110 See my updated post where there is an example of using the function.

[ssd]

OK! StrUpper ("blah blah"); and char *s = "blah blah"; StrUpper (s); does not work; but char s [] = "blah blah"; StrUpper (s); works. Thanks for everyone. As @JoachimPileborg noted, I was trying to crunch a string literal which is a const by def.

[This isn't my real name]

Oddly enough, string literals are not const by definition, they are non-modifiable by definition. String literals are exceptional: they don't become arrays of const char type, they become arrays of char type that you are nevertheless forbidden to modify.