getdtablesize() returns the maximum number of files a process can have open,
one more than the largest possible value for a file descriptor.
The current limit on the number of open files per process.
getdtablesize() is implemented as a libc library function. The glibc version calls
and returns the current
RLIMIT_NOFILE limit, or
OPEN_MAX when that fails.
The libc4 and libc5 versions return
OPEN_MAX (set to 256 since Linux 0.98.4).
SVr4, 4.4BSD (the
getdtablesize() function first appeared in 4.2BSD).