作者：手机用户2602931635 | 来源：互联网 | 2024-10-13 13:18
在做linux下面的网络编程时写了如下一段程序[cpp:showcolumns]viewplaincopy102030405060708090100110120130140150&
在做linux下面的网络编程时写了如下一段程序
[cpp:showcolumns] view plaincopy
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- //&＃xff08;省去N行……&＃xff09;
- char *source,*dest;
- struct in_addr saddr;
- struct in_addr daddr;
- saddr.s_addr &＃61; (in_addr_t)cmd.source.v_uint; //cmd.source.v_uint装载了由字符串通过inet_aton()转化成的源IP的网络字节&＃xff0c;这里无错&＃xff0c;不必深究&＃xff1a;&＃xff09;
- daddr.s_addr &＃61; (in_addr_t)cmd.dest.v_uint; //同上
-
- source &＃61; (char*)inet_ntoa(saddr);
- dest &＃61; (char*)inet_ntoa(daddr);
-
- printf(“source[%s] dest[%s]”,source,dest);
- //&＃xff08;省去N行……&＃xff09;
执行之后打印结果总是源IP和目的IP一样&＃xff0c;如下(程序名为pro)&＃xff1a; &＃xff03;./pro -s 192.1.1.1 -d 192.2.2.2 &＃xff03;source[192.2.2.2] dest[192.2.2.2] 检查了很久都没发现任何错误&＃xff0c;最始还以为赋值时不小心把源IP赋成了目的IP&＃xff0c;但是事实上编写的时候还是比较细心&＃xff0c; 没犯这种错误&＃xff0c;呵呵&＃xff1a;&＃xff09;。 最后一步步排查&＃xff0c;将saddr.s_addr与daddr.s_addr的数值都打印出来了&＃xff0c;发现二者的数值完全不一样&＃xff0c;既然它们两不 一样&＃xff0c;通过inet_ntoa()返回的字符串也应该不一样&＃xff0c;所以&＃xff0c;问题就出在了inet_ntoa()的应用上了。man了一下&＃xff0c;发现了对inet_ntoa的这么一行说明&＃xff1a; The inet_ntoa() function converts the Internet host address in, given
in network byte order, to a string in IPv4 dotted-decimal notation.
The string is returned in a statically allocated buffer, which subse-
quent calls will overwrite.
红色字体的意思是inet_ntoa()返回的字符串是临时装在一个静态分配的缓冲区里面&＃xff0c;下一次调用此函数的时候缓冲区会被重写 。哈哈&＃xff0c;终于发现为什么转化为字符串后&＃xff0c;源地址老是与目的地址一样了&＃xff0c;关键原因在于指针的使用&＃xff0c;前面是将用来装载源地址和目的地址字符串的source与dest声明成了指针&＃xff0c;那么&＃xff0c;赋值之后二者指针就会都指向inet_ntoa()的临时缓冲区里&＃xff0c;在给dest赋值时&＃xff0c;缓冲区被重写了&＃xff0c;所以source指针的值就变成了目的地址&＃xff0c;二者自然就一样了。因此&＃xff0c;改成下面的代码就没问题了&＃xff1a;
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- //(依然省去N行……)
- char source[16],dest[16]; //声明成数组&＃xff0c;可以将内容从缓冲区里复制过来&＃xff0c;面不是用指针指向缓冲区
- int saddr_len,daddr_len;
- struct in_addr saddr;
- struct in_addr daddr;
-
- saddr.s_addr &＃61; (in_addr_t)cmd.source.v_uint;
- daddr.s_addr &＃61; (in_addr_t)cmd.dest.v_uint;
- saddr_len &＃61; strlen(inet_ntoa(saddr));
- daddr_len &＃61; strlen(inet_ntoa(daddr));
-
- if(saddr_len <&＃61;15 && daddr_len <&＃61;15) //IP址的字符串最多为15位
- {
- memcpy(source,inet_ntoa(saddr),saddr_len);
- memcpy(dest,inet_ntoa(daddr),daddr_len);
- source[saddr_len] &＃61; &＃39;/0&＃39;;
- dest[daddr_len] &＃61; &＃39;/0&＃39;;
-
- }else{
- printf("ADDR Error/n");
- exit(1);
- }
- printf(“source[%s] dest[%s]”,source,dest);
-
- //&＃xff08;依然省去N行……&＃xff09;
习惯了用家用电器不看说明书&＃xff0d;_-!&＃xff0c;看来&＃xff0c;以后在使用东西之前还是多看看说明&＃xff0c;少走弯路
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