bsd man page for getdtablesize

GETDTABLESIZE(2)						System Calls Manual						  GETDTABLESIZE(2)

NAME
       getdtablesize - get descriptor table size

SYNOPSIS
       nfds = getdtablesize()
       int nfds;

DESCRIPTION
       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 call getdtablesize returns the size of this table.

SEE ALSO
       close(2), dup(2), open(2), select(2)

4.2 Berkeley Distribution					   June 28, 1985						  GETDTABLESIZE(2)