comparing a string to multiple array in c

Question

End game was to compare the extensions of files in the directory to 2 separate string of arrays to that i could sort it and put it 2 different folders..

I am having a problem comparing the strings of two different arrays.. esp with 2 different sized string arrays..

any suggestions is appreciated..

#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <string.h>

int main (void)
{
 DIR *dirP;
 struct dirent *dp;
 char *fileN; int i = 0;
 char *extMov[]= {".mp4",".flv"};
 char *extMusic[]= {".mp3"};

 dirP = opendir ("/Users/abc/Downloads");
 if (dirP != NULL)
 {
  while ((dp = readdir(dirP)) != NULL)
  {
   if((fileN = strrchr(dp->d_name,'.')) != NULL)
   {
    for (i=0; extMov[i] != NULL; i++)
    {
     if(strcmp (fileN,extMov[i]) == 0)
     {
      printf("%s\n",dp->d_name);
     }
    }
   }
  }
  closedir(dirP);
 }
 else
  perror (" Could not open the directory\n");
 return 0;
}

Some programmer dude · Accepted Answer · 2014-07-12 21:34:16Z

1

The big problem you have is that arrays are not normally terminated in any way. So in your loop

for (i=0; extMov[i] != NULL; i++)

you will most likely step out of bounds, and continue iterating untill there is a NULL somewhere in memory, which might be quite far out of bounds. Accessing an array out of bounds leads to undefined behavior and makes your whole program suspect of errors and illegalities, even though it might compile fine and without warnings.

To solve this problem you can use a little trick to calculate the number entries in an array:

for (i=0; i < sizeof(extMov) / sizeof(extMov[0]); i++)

Do note however that this trick only works on proper arrays. You have to remember that arrays often decays to pointer, for example when passing an array as argument to a function, and then this trick will not work.

answered Jul 12, 2014 at 21:34

Some programmer dude

411k36 gold badges420 silver badges655 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

vinay Over a year ago

this idea definitely works.. but is there a way to compare 2 arrays in this case , extMov and extMusic in a single pass(of for loop)? the problem i face is both arrays will be of different so i will need 2 for loops to do the job...

MoiTux Over a year ago

If the size of the array are not the same yes using two for loops will be the best choice.

MoiTux · Accepted Answer · 2014-07-12 22:39:23Z

1

your for loop is looking for a NULL value to stop, but you didn't set a NULL value to your array.
So this extMov[i] != NULL might never be found (depending on the content of your memory)

char *extMov[]= {".mp4",".flv", NULL};

I explicitly add a NULL as the last entry of my array to be sure to have it.

answered Jul 12, 2014 at 22:39

MoiTux

8187 silver badges17 bronze badges

Collectives™ on Stack Overflow

comparing a string to multiple array in c

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related