Solution for finding file with set extension in directory

/* You will need to include the following headers on your C++ class declaration file  the all works
*
*Info on this  can be found at this address  http://www.gnu.org/software/libc/manual/html_node/
* Reading_002fClosing- Directory.html#Reading_002fClosing-Directory
*/


#include <dirent.h>
#include <sys/types.h>
#include <cstring>


void ReadFile::listFiles(const char* dirname)
{
    DIR *di;
    char *ptr1,*ptr2;
    int retn;
    struct dirent *dir;
    di = opendir(dirname); //specify the directory name
    if (di)
    {
        while ((dir = readdir(di)) != NULL)
        {
            ptr1=strtok(dir->d_name,dirname);
            ptr2=strtok(NULL,".");
            if(ptr2!=NULL)
            {
                retn=strcmp(ptr2,"txt");
                if(retn==0)
                {
                    printf("%s\t",ptr1);
                }
            }
        }
        closedir(di);
    }



}