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():
");
   printf("   x is %d and is stored at %p.
", x, &x);
   printf("   xptr points to %p which holds %d.
", xptr, *xptr);
   display(x, xptr);
   return 0;
}

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

使用上面的file， 比方 test.c

1, 编译。 gcc -g -o testx test.c

2, 执行。 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>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
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, 运行。

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. ", 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