APUE中对出错函数的封装

//   输出至标准出错文件的出错处理函数static void err_doit(int, int, const char *, va_list);

/*
 * Nonfatal error related to a system call
 * Print a message and return
 */
void err_ret(const char *fmt, ...)
{
   va_list ap;

   va_start(ap, fmt);
   err_doit(, 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(, errno, fmt, ap);
   va_end(ap);
   exit();
}

/*
 * 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(, error, fmt, ap);
   va_end(ap);
   exit();
}

/*
 * 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(, errno, fmt, ap);
   va_end(ap);
   abort();          /* dump core and terminate */
   exit();          /* shouldn't get here */
}

/*
 * Nonfatal error unrelated to a system call
 * Print a message and return
 */
void err_msg(const char *fmt, ...)
{
   va_list ap;

   va_start(ap, fmt);
   err_doit(, , 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(, , fmt, ap);
   va_end(ap);
   exit();
}

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 the same */
   fputs(buf, stderr);
   fflush(NULL);               /* flushes all stdio  output streams */
}