代码

#include <stdio.h>
#include <netdb.h>
int main()
{
        struct hostent *he;
        char hostname[40]={0} ;
        char ipaddr[40]={0};


        gethostname(hostname,sizeof(hostname));
        he = gethostbyname(hostname);
        printf("%d-handle-gethostbyname\n",he);
        printf("hostname=%s\n",hostname);
        //printf("%s\n",inet_ntoa(*(struct in_addr*)(he->h_addr)));
	char destIP[128];
	char **phe = NULL;
	for( phe=he->h_addr_list ; NULL != *phe ; ++phe)
	{
		inet_ntop(he->h_addrtype,*phe,destIP,sizeof(destIP));
		printf("addr:%s\n",destIP);
    
	}
}

编译
 cc -g gh.c -o gh
调试
[root@xxx ~]# gdb gh
GNU gdb (GDB) Red Hat Enterprise Linux (7.0.1-32.el5_6.2)
Copyright (C) 2009 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 "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/codeman/gh...done.
(gdb) l   //显示程序代码
1       #include <stdio.h>
2       #include <netdb.h>
3       int main()
4       {
5               struct hostent *he;
6               char hostname[40]={0} ;
7               char ipaddr[40]={0};
8
9               gethostname(hostname,sizeof(hostname));
10              he = gethostbyname(hostname);
(gdb) l     //继续显示程序代码
11              printf("%d-handle-gethostbyname\n",he);
12              printf("hostname=%s\n",hostname);
13              //printf("%s\n",inet_ntoa(*(struct in_addr*)(he->h_addr)));
14       char destIP[128];
15        char **phe = NULL;
16       for( phe=he->h_addr_list ; NULL != *phe ; ++phe){
17              inet_ntop(he->h_addrtype,*phe,destIP,sizeof(destIP));
18              printf("addr:%s\n",destIP);
19          
20          }
(gdb) l //继续显示程序代码
21      }
(gdb) l //继续显示程序代码
Line number 22 out of range; gh.c has 21 lines.
(gdb) break 1  //设置断点在第一行
Breakpoint 1 at 0x400593: file gh.c, line 1.
(gdb) break 15 //再设置断点在第15行
Breakpoint 2 at 0x400629: file gh.c, line 15.
(gdb) r //启动调试程序
Starting program: /home/codeman/gh 
warning: no loadable sections found in added symbol-file system-supplied DSO at 0x2aaaaaaab000


Breakpoint 1, main () at gh.c:6
6               char hostname[40]={0} ;
(gdb) n //现在到达断点了，继续走一行【单步】
7               char ipaddr[40]={0};
(gdb) n //再走一行【单步】
9               gethostname(hostname,sizeof(hostname));
(gdb) print hostname //打印变量 hostname
$1 = '\000' <repeats 39 times>
(gdb) n //再走一行【单步】
10              he = gethostbyname(hostname);
(gdb) print hostname //打印变量 hostname
$2 = "xxx.ooo.yyy.net", '\000' <repeats 17 times>
(gdb) bt //打印堆栈
#0  main () at gh.c:10
(gdb) c //继续往下走，到下一断点去
Continuing.
1836408896-handle-gethostbyname
hostname=xxx.ooo.yyy.net


Breakpoint 2, main () at gh.c:15
15        char **phe = NULL;
(gdb) n //现在到达15行的断点了，再走一步
16       for( phe=he->h_addr_list ; NULL != *phe ; ++phe){
(gdb) print he //打印变量
$3 = (struct hostent *) 0x356d756040
(gdb) print he->h_addr_list //打印变量
$4 = (char **) 0x601020
(gdb) print he->h_addr_list[0] //打印变量
$5 = 0x601010 "\177"
(gdb) print he->h_addr_list[1] //打印变量
$6 = 0x0
(gdb) c //继续往下走，到下一断点去，实际是跑完了
Continuing.
addr:127.0.0.1


Program exited normally.
(gdb) q //退出gdb
[root@xxx ~]#