Chapter 8

D.3 Standard Error Functions

We define our own set of error functions that are used throughout the text to handle error conditions. The reason for using our own error functions is to let us write our error handling with a single line of C code, as in

 if  (error condition)  err_sys  (printf format with any number of arguments)  ; 

instead of

 if  (error condition)  { char buff [2002]; snprintf (buff, sizeof (buff),  printf format with any number of arguments)  ; perror(buff); exit (1); } 

Our error functions use the variable-length argument list facility from ANSI C . See Section 7.3 of [Kernighan and Ritchie 1988] for additional details.

Figure D.3 lists the differences between the various error functions. If the global integer daemon_proc is nonzero, the message is passed to syslog with the indicated level; otherwise , the error is output to standard error.

Figure D.3. Summary of our standard error functions.

Figure D.4 shows the first five functions from Figure D.3.

Figure D.4 Our standard error functions.

lib/error.c

 1 #include "unp.h" 2 #include <stdarg.h> /* ANSI C header file */ 3 #include <syslog.h> /* for syslog() */ 4 int daemon_proc; /* set nonzero by daemon_init() */ 5 static void err_doit(int, int, const char *, va_list); 6 /* Nonfatal error related to system call 7 * Print message and return */ 8 void 9 err_ret(const char *fmt, ...) 10 { 11 va_list ap; 12 va_start(ap, fmt); 13 err_doit(1, LOG_INFO, fmt, ap); 14 va_end(ap); 15 return; 16 } 17 /* Fatal error related to system call 18 * Print message and terminate */ 19 void 20 err_sys(const char *fmt, ...) 21 { 22 va_list ap; 23 va_start(ap, fmt); 24 err_doit(1, LOG_ERR, fmt, ap); 25 va_end(ap); 26 exit(1); 27 } 28 /* Fatal error related to system call 29 * Print message, dump core, and terminate */ 30 void 31 err_dump(const char *fmt, ...) 32 { 33 va_list ap; 34 va_start(ap, fmt); 35 err_doit(1, LOG_ERR, fmt, ap); 36 va_end(ap); 37 abort(); /* dump core and terminate */ 38 exit(1); /* shouldn't get here */ 39 } 40 /* Nonfatal error unrelated to system call 41 * Print message and return */ 42 void 43 err_msg(const char *fmt, ...) 44 { 45 va_list ap; 46 va_start(ap, fmt); 47 err_doit(0, LOG_INFO, fmt, ap); 48 va_end(ap); 49 return; 50 } 51 /* Fatal error unrelated to system call 52 * Print message and terminate */ 53 void 54 err_quit(const char *fmt, ...) 55 { 56 va_list ap; 57 va_start(ap, fmt); 58 err_doit(0, LOG_ERR, fmt, ap); 59 va_end(ap); 60 exit(1); 61 } 62 /* Print message and return to caller 63 * Caller specifies "errnoflag" and "level" */ 64 static void 65 err_doit(int errnoflag, int level, const char *fmt, va_list ap) 66 { 67 int errno_save, n; 68 char buf[MAXLINE + 1]; 69 errno_save = errno; /* value caller might want printed */ 70 #ifdef HAVE_VSNPRINTF 71 vsnprintf(buf, MAXLINE, fmt, ap); * safe */ 72 #else 73 vsprintf(buf, fmt, ap); /* not safe */ 74 #endif 75 n = strlen(buf); 76 if (errnoflag) 77 snprintf(buf + n, MAXLINE - n, ": %s", strerror(errno_save)); 78 strcat(buf, "\n"); 79 if (daemon_proc) { 80 syslog(level, buf); 81 } else { 82 fflush (stdout); /* in case stdout and stderr are the same */ 83 fputs(buf, stderr); 84 fflush(stderr); 85 } 86 return; 87 }