Determine the number of open files in your program (C/C++)

The code below will display the number of files open by the running process. It does this by getting the maximum file descriptor number and then iterating through each possible fd trying to do an 'fstat' on it. If errno returns anything other than EBADF 'file descriptor is bad' it increments a count.

It is fairly portable, tested and working on Linux & Solaris.

/*
 * ofiles.c - Displays the number of open files for its own process
 * Copyright (C) 2005 Michael Cutler <m@cotdp.com>
 *
 */

#include <stdio.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>

extern int errno;

int main ( int argc, char** argv, char** env ) {

   int i = 0;
   int fd_counter = 0;
   int max_fd_number = 0;
   struct stat   stats;
   struct rlimit rlimits;

   max_fd_number = getdtablesize();

   getrlimit(RLIMIT_NOFILE, &rlimits);

   printf( "max_fd_number: %d\n", max_fd_number );
   printf( "     rlim_cur: %d\n", rlimits.rlim_cur );
   printf( "     rlim_max: %d\n", rlimits.rlim_max );

   for ( i = 0; i <= max_fd_number; i++ ) {
      fstat(i, &stats);
      if ( errno != EBADF ) {
         fd_counter++;
      }
   }

   printf( "   open files: %d\n", fd_counter );

   return 0;

}

Example:

[mcutler@rasco ~]$ gcc -o ofiles ofiles.c
[mcutler@rasco ~]$ ./ofiles
max_fd_number: 1024
     rlim_cur: 1024
     rlim_max: 1024
   open files: 3
[mcutler@rasco ~]$

About this entry

You’re currently reading “Determine the number of open files in your program (C/C++),” an entry on Weblog of Michael Cutler

Published:
22nd August 2005 / 12:08pm
Category:
Uncategorised

Related Entries