Apue.h in advanced programming of UNIX environment

/************** * *apueerror.h * *************/#include <apue.h> #include <stdio.h> #inc    
         
Lude <errno.h>/* for definition of errno */#include <stdarg.h>/* ISO C variable aruments * *    
static void Err_doit (int, int, const char *, va_list);  
 * * Nonfatal error related to a system call.  
 * Print A and return.    
*/void Err_ret (const char *FMT, ...)    
         
    {va_list ap;    
    Va_start (AP, FMT);    
    Err_doit (1, errno, FMT, AP);    
Va_end (AP);  
 } * * Fatal error related to a system call.  
 * Print a message and terminate.    
*/void Err_sys (const char *FMT, ...)    
         
    {va_list ap;    
    Va_start (AP, FMT);    
    Err_doit (1, errno, FMT, AP);    
    Va_end (AP);    
Exit (1);  
 } * * Fatal error unrelated to a system call.  
 * Error code passed as explict parameter. * Print a message and terMinate.    
*/void Err_exit (int error, const char *FMT, ...)    
         
    {va_list ap;    
    Va_start (AP, FMT);    
    Err_doit (1, error, FMT, AP);    
    Va_end (AP);    
Exit (1);  
 } * * Fatal error related to a system call.  
 * Print a message, dump core, and terminate.    
*/void Err_dump (const char *FMT, ...)    
         
    {va_list ap;    
    Va_start (AP, FMT);    
    Err_doit (1, errno, FMT, AP);    
    Va_end (AP); Abort (); /* Dump core and Terminate */exit (1);  
 /* shouldn ' t get here/* nonfatal error unrelated to a system call.  
 * Print A and return.    
*/void Err_msg (const char *FMT, ...)    
         
    {va_list ap;    
    Va_start (AP, FMT);    
    Err_doit (0, 0, FMT, AP);    
Va_end (AP);  
 } * * Fatal error unrelated to a system call.  
 * Print a message and terminate.    
*/void Err_quit (const char *FMT, ...)   { 
    Va_list ap;    
    Va_start (AP, FMT);    
    Err_doit (0, 0, FMT, AP);    
    Va_end (AP);    
Exit (1);  
 /* Print a message and return to caller.  
 * Caller Specifies "Errnoflag".    
   */static void Err_doit (int errnoflag, int error, const char *FMT, va_list ap) {char buf[maxline];    
   vsnprintf (buf, Maxline, FMT, AP);    
   if (Errnoflag) snprintf (Buf+strlen (BUF), Maxline-strlen (BUF), ":%s", strerror (Error));    
   strcat (buf, "\ n"); Fflush (stdout);    
   /* In case stdout and stderr are same * * fputs (buf, stderr); Fflush (NULL); /* Flushes all stdio output streams */}