C/Count free file descriptors
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This could be improved to detect the number of file descriptors set by ulimit, but most systems are set to ~1024 by default.
{ int i, fd[2048]; for (i = 0; i < sizeof(fd) / sizeof(int); i++) { if ((fd[i] = open("/dev/null", O_RDONLY)) == -1) break; } printf("free fds: %d\n", i); for (i-- ; i >= 0; i--) { close(fd[i]); } }