C seg fault

drigz · 10-01-2004, 01:36 PM

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.