opendir: Too many open files - c

Question

I write this code to print all files in /home/keep with absolution path:
#include <dirent.h>
#include <sys/stat.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
void catDIR(const char *re_path);
int main(int argc, char *argv[])
{
char *top_path = "/home/keep";
catDIR(top_path);
return 0;
}
void catDIR(const char *re_path)
{
DIR *dp;
struct stat file_info;
struct dirent *entry;
if ((dp = opendir(re_path)) == NULL)
{
perror("opendir");
return;
}
while (entry = readdir(dp))
{
if (entry->d_name[0] == '.')
continue;
//get Absolute path
char next_path[PATH_MAX];
strcpy(next_path, re_path);
strcat(next_path, "/");
strcat(next_path, entry->d_name);
lstat(next_path, &file_info);
if (S_ISDIR(file_info.st_mode))
{
catDIR(next_path);
}
else
{
printf("%s/%s\n", re_path, entry->d_name);
}
}
free(dp);
free(entry);
}
When I run it.
Not only print some file's path, but also print some error message:
opendir: Too many open files
I read man 3 opendir, then realize, I had opened too many files.
I do want to know, how to close it? and how to correct this program

Answer 1

You should probably use closedir when you finish iterating through a directory's contents.
Also, you might want to read the directory's listing into an array, close the directory, and then recurse on the array. This might help with traversing very deep directory structures.

Answer 2

Run
cat /proc/sys/fs/file-nr
what does it give ?
output format is : (number of allocated file handlers) - (number of allocated but unused file handlers) - (maximum number of file handlers)
If you get more number of allocated but unused file handlers, it means that you've to close directories as mentioned by #Matthew Iselin.
You can also change system limit.
More info about changing system limit Can be found here.