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drigz

10-01-2004 01:36 PM

C seg fault

This code segfaults on the first strtok:

Code:

int mkdirp(char* file)

{

        printf("%s\n", file);

        char* pch;

        pch = strtok(file,"/");

        while (pch != NULL)

        {

                printf("%s\n", pch);

                mkdir(pch, 0777);

                pch = strtok(NULL, "/");

        }

        return 0;

}

I have tried calling it with file = "newdir" and file = "mydir/subdir" - neither work.

itsme86

10-01-2004 01:51 PM

You can't use strtok() on string constants according to the man page:

Code:

BUGS

      Never use these functions. If you do, note that:



              These functions modify their first argument.



              These functions cannot be used on constant strings.

So if main() looks like:

Code:

int main(void)

{

  mkdirp("newdir");

  return 0;

}

...it will crash. But this should work:

Code:

int main(void)

{

  char dirname[] = "newdir";



  mkdirp(dirname);

  return 0;

}

drigz

10-01-2004 02:47 PM

still fails - this is now the relevant part of my main:

Code:

        char* newdir="newdir";

        mkdirp(newdir);

        printf("made newdir\n");

        char* mydir="mydir/subdir";

        mkdirp(mydir);

        printf("made mydir/subdir\n");

        char* newdir2="newdir2/subdir";

        mkdirp(newdir2);

        printf("made newdir2/subdir\n");

since it said i shouldnt use it, is there an alternative to using this (other than making the behaviour myself)?

itsme86

10-01-2004 03:06 PM

This:

Code:

char* newdir="newdir";

...is not the same as...

Code:

char dirname[] = "newdir";

...like I suggested.

It's still segfaulting for you because you're still using a string constant. Use my suggestion and it will work fine.

drigz

10-01-2004 03:14 PM

really? oh well - i just gave up and wrote it myself (turns out i forgot something and it was easier to write it myself)

thanks.

itsme86

10-01-2004 03:35 PM

Yeah, string constants such as "newdir" go into read-only memory. So when you do char *name = "newdir"; you're just creating a pointer that points to read-only memory, but when you do char name[] = "newdir"; you're creating an array and copying the contents of "newdir" into the array. The memory for the array is not in read-only memory.

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