它是调用./segfault的shell。如果你在你的计算机上切换到dash并运行同样的命令，你也不会在那里看到 Segmentation fault 消息。

1.定义任何变量/对象时，始终对其进行初始化。
1.使用任何指针时，仅在非NULL时使用它们
1.以下示例程序在接收SIGSEGV信号时调用用户定义的函数“mysig”。当我们使用NULL指针时，程序接收信号SIGSEGV（分段错误）。我更新了代码，以便在发生分段错误时调用“mysig”。一旦发生分段错误，它将使用默认函数创建核心转储文件。一旦接收到该信号，它将
1.在执行程序之前：

$ ulimit -c unlimited
$ ./a.out

上面的程序将创建一个核心文件。使用核心文件，我们可以分析程序崩溃的地方使用gdb.exe/gdb/dbx基于您的操作系统。gdb教程在线：

https://www.tutorialspoint.com/gnu_debugger/index.htm

示例程序：

# include <sys/signal.h>

# include <stdio.h>

void mysig( int sig)
{
        switch( sig )
        {
                case SIGSEGV:
                        printf("Never use NULL pointer\n");
                        signal( SIGSEGV, SIG_DFL);
                        break;
                default:
                        printf( "Other signal: %d\n", sig);
        }
}
int main()
{
        int* p = NULL;
        signal( SIGSEGV, mysig);
        if ( NULL == p )
        {
                printf("Never use NULL pointer\n");
        }
        else
        {
                printf("%d\n", *p);
        }
        printf( "Make call to mysig by using NULL pointer\n");
        printf("%d\n", *p);
        return 0;
}

示例输出：

$ gcc  -g -Wall 73596388.cpp -o ./a.out
$ ./a.out
Never use NULL pointer
Make call to mysig by using NULL pointer
Never use NULL pointer
Segmentation fault (core dumped)
$ # I compiled using bash.exe/gcc.exe at windows:
$ gdb a.out
Reading symbols from a.out...
(gdb) break main
Breakpoint 1 at 0x1004010d8: file 73596388.cpp, line 17.
(gdb) run
Starting program: ./a.out
[New Thread 10964.0x219c]
[New Thread 10964.0x2090]
[New Thread 10964.0x1dd4]

Thread 1 "a.out" hit Breakpoint 1, main () at 73596388.cpp:17
17              int* p = NULL;
(gdb) next
18              signal( SIGSEGV, mysig);
(gdb) next
19              if ( NULL == p )
(gdb) next
21                      printf("Never use NULL pointer\n");
(gdb) next
Never use NULL pointer
27              printf( "Make call to mysig by using NULL pointer\n");
(gdb) next
Make call to mysig by using NULL pointer
28              printf("%d\n", *p);
(gdb) step

Thread 1 "a.out" received signal SIGSEGV, Segmentation fault.
0x0000000100401136 in main () at 73596388.cpp:28
28              printf("%d\n", *p);
(gdb) step
Never use NULL pointer

Thread 1 "a.out" received signal SIGSEGV, Segmentation fault.
0x0000000100401136 in main () at 73596388.cpp:28
28              printf("%d\n", *p);
(gdb) step
      0 [main] a.out 33539 cygwin_exception::open_stackdumpfile: Dumping stack trace to a.out.stackdump
                                                                                                       [Thread 10964.0x2adc exited with code 35584]
[Thread 10964.0x2090 exited with code 35584]
[Thread 10964.0x219c exited with code 35584]
[Inferior 1 (process 10964) exited with code 0105400]
(gdb)