Directory reading

Hello fellow programmers,
I am having a problem running across a method of opening, reading filenames, and closing a directory in order to pull filenames with a certain extension from. In searching, the only reference I found to accomplish such a task was on the delorie/djgpp website. I am using Dev-C++ version 4.9.7.6. On the web site, they posted an example program to explain how it was used. Just for my sake, I tried the program and got some errors. Following is the program code and the errors. I am not asking for anybody to write my code, just for some knowledge in determining where the problem is.

Code:

/*****************CODE**************************/
#include <sys/types.h>
#include <dirent.h>		/* Directory information.*/

main()
{
  DIR * dir_p;
  struct dirent * dir_entry_p;
   
			/* Open the current directory*/	
  dir_p = opendir(".");

			/* read each entry until NULL.*/

  while( NULL != (dir_entry_p = readdir(dir_p)))
  {
		/* print the name of the file held in 
		 * this directory entry.*/

    printf(" %s \n", dir_entry_p->d_name);
  }

				/* Tidy up.*/
  closedir(dir_p);
}

****************ERRORS****************************
[Linker error] undefined reference to `opendir'
[Linker error] undefined reference to `readdir'
[Linker error] undefined reference to `closedir'
************************************************** *

The code is exactly how it was downloaded as a file. I am just doing some testing in order to determine how to implement in to my own program. Any help would be greatly appreciated.

Thankfully,
Kendal

For some reason on my system it does not work.
Like I said I get the following errors:

[Linker error] undefined reference to `opendir'
[Linker error] undefined reference to `readdir'
[Linker error] undefined reference to `closedir'

I am using Dev-C++, the latest version 4.9.7.6 and checked the dirent.h header file and it does make reference to opendir, readdir, and closedir. Any ideas why I get such a linker error??? Would you like to see my dirent.h header file???