getdtablesize - get descriptor table size
Standard C Library (libc, -lc)
#include <unistd.h>
int
getdtablesize(void);
Each process has a fixed size descriptor table, which is guaranteed to
have at least 20 slots. The entries in the descriptor table are numbered
with small integers starting at 0. The getdtablesize() system call
returns the size of this table.
close(2), dup(2), open(2), select(2)
The getdtablesize() system call appeared in 4.2BSD.