text: #include "apue.h"
  #include <errno.h>
  #include <limits.h>
  
  #ifdef OPEN_MAX
  static long openmax = OPEN_MAX;
  #else
  static long openmax = 0;
  #endif
  
  /*
   *If OPEN_MAX is indeterminate, this might be inadequate.
   */
   #define OPEN_MAX_GUESS 256
  
   long
   open_max(void)
   {
   	if (openmax == 0) {	/* first time through*/
   		errno = 0;
  
  	 	if ((openmax = sysconf(_SC_OPEN_MAX)) < 0)
  	 	{
  	 		if (errno == 0)
  	 			openmax = OPEN_MAX_GUESS; /* it's indeterminate 不明确的 */
  	 	}
   	}
   	return(openmax);0
   }