Segmentation Fault On Number Increment

[OzWolf]

Hey folks,

I'll be the first to admit that the last time I did any serious C programming was over a decade ago at uni. Up until today, my work with C has been basic maintenance and minor code changes.

Anyway, I'm running into a segmentation fault that just has me reviving my days in the Navy with cursing.

Here's the function causing the problem:

int dir_parts(char *dir_name){
    int i;
    int j;
    char c[2];

    j = 0;

    for (i = 0; i < strlen(dir_name); i++){
        strcpy(c, getsub(dir_name, i, i));
        if (strcmp(c, "/") == 0){
            j++;
        }
    }

    if (strcmp(c, "/") != 0){
        j++;
    }

    return(j);
}

The bit in particular is the last j++ statement. It's driving me spare. If I just put a printf in there with the strcmp outcome, the ENTIRE program runs fine. If I put anything except the j++ line in, the program runs fine (though the function returns a number one less than the intended amount).

After figuring out my char memory problems, this one has me wanting a stiff drink.

Any help greatly appreciated.

 

[Salem]

> getsub(dir_name, i, i)
You seem to be copying increasingly long strings into an array of only 2 characters (thus trashing something else).

An alternative is using strchr() to find each /, then resume the search from the next char in the string.
This has the advantage of no copying.



--
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.

 

[ArkM]

What for strcmp or strchr? Keep it simple:

for (i = j = 0; fir_name[i]; ++i)
    if (dir_name[i] == '/')
       ++j;

 

[OzWolf]

Thanks for the tips guys. I changed the function to:

int dir_parts(char *dir_name){
    int i;
    int j;
    char c[2];

    for (i = j = 0; dir_name[i]; ++i)
        if (dir_name[i] == '/')
            ++j;

    if (dir_name[i] != '/'){
        ++j;
    }

    return(j);
}

But I still get a core dump on the code:

if (dir_name[i-1] != '/'){
    ++j;
}

Both my original code and the modified one above worked fine until I put the extra j increment in the if-statement. I'm assuming because I can put a successful printf("%c\n", dir_name[i-1]) into the if-statement and output the last character of dir_name, the problem is with the increment of j, not of anything to do with the string, which is what is bugging the hell out of me.

 

[ArkM]

You place this statement in the function body:

    if (dir_name[i] != '/'){
        ++j;

Why?
dir_name == '\0' after loop (see loop condition).
If no slashes in the dir_name
then j == 0 - and you have wrong memory access
in dir_name[-1]...

 

[OzWolf]

I've fixed the issue. Obviously the ++j was the last straw in a memory issue elsewhere.

After a re-coding of the program, the last function I wrote out works without a hitch.

And that if statement was supposed to be:

if (dir_name[i-1] != '/'){
    ++j;
}

Primary reason for the last bit is if the user-entered directory this is helping create bread-crumbs for is missing a / from the end (ie. /archive/files instead or /archive/files/).