Copying the end of a string

**binks** · 06-12-2012

Hello,

So I have a string with a full filepath. However, I only want the immediate filename, without the full path. How can I remove the other bits or even just copy the part I want into another variable. Here is how it should work from what I can gather.

Code:

char file[] = "C:\\Users\\Administer\\Desktop\\doc.txt";

// find last occurence of '\'
char *location = strrchr(file, '\');

// last occurence is now in location

So now how can I copy the rest of the string AFTER the last '\'? What am I missing though, or is there an easier approach?

In the end I would like to convert this

Code:

char file[] = "C:\\Users\\Administer\\Desktop\\doc.txt";
/* to this */
char newName[] = "doc.txt";

**laserlight** · 06-12-2012

Try this test program:

Code:

#include <stdio.h>
#include <string.h>

int main(void)
{
    char file[] = "C:\\Users\\Administer\\Desktop\\doc.txt";

    char *location = strrchr(file, '\\');

    printf("%s\n", location + 1);

    return 0;
}

Do you see how to proceed from here?

**Deckard** · 06-12-2012

I suppose you could always start at the NULL and work your way back to the first occurance of the slash and save yourself the function call (not that there's anything wrong with calling strrchr()).

**laserlight** · 06-12-2012

Originally Posted by Deckard

I suppose you could always start at the NULL and work your way back to the first occurance of the slash and save yourself the function call (not that there's anything wrong with calling strrchr()).

The way I see it, if the function call overhead is not causing some kind of performance problem and if depending on the C standard library is perfectly fine then that would be rather pointless.

**Deckard** · 06-12-2012

It's just another way to skin the cat; it's not criticism.

**christop** · 06-13-2012

Originally Posted by Deckard

I suppose you could always start at the NULL and work your way back to the first occurance of the slash and save yourself the function call (not that there's anything wrong with calling strrchr()).

If you already know where the null terminator is, you ought to know where the last backslash is too, so you can just as easily hardcode an offset into the path to strip off everything but the file name.

More likely you don't know where the null terminator is to begin with, so you would have to search for it (or use strlen) before you can search backwards for the backslash, but by that point you might as well just call strrchr to do the searching for you. Your C implementation most likely has a fast (and well-tested) strrchr which would be difficult to match in performance.

Summary: don't reinvent the wheel.

**binks** · 06-13-2012

Originally Posted by laserlight

Try this test program:

Code:

#include <stdio.h>
#include <string.h>

int main(void)
{
    char file[] = "C:\\Users\\Administer\\Desktop\\doc.txt";

    char *location = strrchr(file, '\\');

    printf("%s\n", location + 1);

    return 0;
}

Do you see how to proceed from here?

Yes, Ok I see it now. I tested it using strcpy as well, and it works. So now I know I can treat location + 1 as a string.

Thanks for the help, I can take it from here

**binks** · 06-13-2012

Ok, I have a problem. What is wrong here?

Code:

char newNames[numFiles][256];
char fileNames[][256] = {"Test1.zip", "Test2.rar"};
int numfiles = 2;

      for(i = 0; i < numFiles; i++)
      {
            char *location = strrchr(fileNames[i], '\\');
            strcpy(newNames[i], location + 1); // crashes here
      }

**antred** · 06-13-2012

Originally Posted by binks

Ok, I have a problem. What is wrong here?

Code:

char newNames[numFiles][256];
char fileNames[][256] = {"Test1.zip", "Test2.rar"};
int numfiles = 2;

      for(i = 0; i < numFiles; i++)
      {
            char *location = strrchr(fileNames[i], '\\');
            strcpy(newNames[i], location + 1); // crashes here
      }

If the string you pass to strrchr() doesn't contain the character you want it to look for, strrchr() returns a null pointer. You then pass this null pointer to strcpy(). The strcpy() function cannot deal with a null pointer, especially if you add 1 to that null pointer (which means it's not really a null pointer anymore ... it's just a bogus pointer).

**binks** · 06-13-2012

So after I call strrchr, I should check to see if:

Code:

if(location == NULL)

Or do I have to go

Code:

strcmp(location, NULL);

**antred** · 06-13-2012

The former. If location is null then strrchr() has failed to find a backslash in the path name, which means ... ah screw it, I'll just show you what I mean:

Code:

char newNames[numFiles][256];
char fileNames[][256] = {"Test1.zip", "Test2.rar"};
int numfiles = 2;
 
      for(i = 0; i < numFiles; i++)
      {
            char *location = strrchr(fileNames[i], '\\');
            if ( location )
            {
                strcpy(newNames[i], location + 1);
            }
            else
            {
                // path contains no backslash
                strcpy(newNames[i], fileNames[i]);
            }
      }

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