using gdb to debug c program

#include <stdio.h>
static void display(int i, int *ptr);

int main(void) {
   int x = 5;
   int *xptr = &x;
   printf("In main():\n");
   printf("   x is %d and is stored at %p.\n", x, &x);
   printf("   xptr points to %p which holds %d.\n", xptr, *xptr);
   display(x, xptr);
   return 0;
}

void display(int z, int *zptr) {
   printf("In display():\n");
   printf("   z is %d and is stored at %p.\n", z, &z);
   printf("   zptr points to %p which holds %d.\n", zptr, *zptr);
}

使用上面的file， 比如 test.c

1, 编译。 gcc -g -o testx test.c

2, 运行。 gdb testx

GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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and "show warranty" for details.
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Type "show configuration" for configuration details.
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<http://www.gnu.org/software/gdb/bugs/>.
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For help, type "help".
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Reading symbols from testx...done.
(gdb)

3, 设置断点。 gdb> b 8

Breakpoint 1 at 0x8048472: file test.c, line 8.

4, 设置断点2。 gdb> b 10

Breakpoint 2 at 0x80484ac: file test.c, line 10.

5, 执行。 gdb> run

Starting program: /home/wang/mytest/gdbtest/testx 
In main():


Breakpoint 1, main () at test.c:8
8   printf("   x is %d and is stored at %p.\n", x, &x);

6, 继续。 gdb> c

Continuing.
   x is 5 and is stored at 0xbfffeb58.
   xptr points to 0xbfffeb58 which holds 5.


Breakpoint 2, main () at test.c:10
10   display(x, xptr);

7, 继续。 gdb> c

Continuing.
In display():
   z is 5 and is stored at 0xbfffeb40.
   zptr points to 0xbfffeb58 which holds 5.
[Inferior 1 (process 11616) exited normally]

9, for step, using step

10, for backtrace, using bt