ctime()导致SIGABRT (?!)

Question

代码如下：

void i_log_ (int error, const char * file, int line, const char * fmt, ...)
{
     /* Get error description */
     char * str_err = get_str_error (errno);
     remove_trailing_newl (str_err);

     /* Format string and parameters */
     char message [1024];
     va_list ap;
     va_start (ap, fmt);
     vsprintf (message, fmt, ap);
     va_end (ap);

     /* Get time */
     time_t t = time (NULL);
     char stime [64];
     char * temp = ctime (&t);
     strncpy (stime, temp, sizeof stime - 1);
     remove_trailing_newl (stime);

     FILE * log;


#ifdef __WIN32__
#else
# ifdef P_LISTENER
     log = fopen (I_LOG_FILE, "a+b");
     flock (fileno (log), LOCK_EX);
# else /* shared file descriptor of log, lock before opening */
     pthread_mutex_lock (& mutex);
     log = fopen (I_LOG_FILE, "a+b");
# endif
#endif

     if (log) {
          if (error)
               fprintf (log, ERR_FORMAT, stime, file, line, str_err, message);
          else
               fprintf (log, ERR_FORMAT_NO_ERRNO, stime, file, line, message);
     }

#ifdef __WIN32__
     free (str_err);
#else
# ifdef P_LISTENER
     flock (fileno (log), LOCK_UN);
     fclose (log);
# else
     fclose (log);
     pthread_mutex_unlock (& mutex);
# endif
#endif
     return;
}

虽然有锁定机制，但在这种情况下，函数不会并发调用，所以我认为这不是问题所在。但是，该程序会收到一个SIGABRT

[...]
(gdb) c
Continuing.

Program received signal SIGHUP, Hangup. // It's OK, I sent this.
0x00dee416 in __kernel_vsyscall ()
(gdb) c
Continuing.

Program received signal SIGABRT, Aborted.
0x00dee416 in __kernel_vsyscall ()
(gdb) up
#1  0x0013ae71 in raise () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#2  0x0013e34e in abort () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#3  0x00171577 in ?? () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#4  0x0017b961 in ?? () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#5  0x0017d28b in ?? () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#6  0x0018041d in free () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#7  0x0019b0d2 in ?? () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#8  0x0019b3c5 in ?? () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#9  0x00199a9f in localtime () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#10 0x00199951 in ctime () from /lib/i386-linux-gnu/libc.so.6
(gdb) up
#11 0x08049634 in i_log_ (error=0, file=0x804b17d "src/group.c", line=53, fmt=0x804b128 "Setting up new configuration: listener type: %s, number: %d, http-log: %s, port: %d.") at src/error.c:42
42       char * temp = ctime (&t);
(gdb) print temp
$1 = 0x260000 ""
(gdb) print t
$2 = 1329935482
(gdb) print &t
$3 = (time_t *) 0xbff8a5b8
(gdb) 

我一点也不知道。ctime返回一个空字符串，手册页没有提到这种情况。仔细想想，我不明白为什么它会返回一个空字符串，以及这段代码有什么问题。

任何帮助都是非常感谢的。

Answer 1

ctime没有返回空字符串。它还没有返回，因为它在尝试做自己的事情时崩溃了。

崩溃发生在free()内部，因此您可能在调用ctime()之前的某个时刻损坏了内存。如果你在支持的平台上运行，尝试使用Valgrind这样的工具来检查你的内存访问。

Answer 2

由于崩溃发生在ctime()内部，并且您传递的指针是有效的，所以问题很可能是您已经在其他地方践踏了内存边界(堆栈跟踪中有free() )，并且问题只在这里表现出来。