Linux网络编程IPv4和IPv6的inet_addr、inet_aton、inet_pton函数
知识背景：210.25.132.181属于IP地址的ASCII表示法，也就是字符串形式。英语叫做IPv4 numbers-and-dots notation。
如果把210.25.132.181转换为整数形式，是3524887733，这个就是整数形式的IP地址。英语叫做binary data。（其实binary是二进制的意思）
详细介绍，请参考： 网络字节序与主机字节序的转换
问题所在：
如何在字符串形式的IP和整数形式的IP之间转换呢？
转换函数：
int inet_aton(const char *cp, struct in_addr *inp);
in_addr_t inet_addr(const char *cp);
in_addr_t inet_network(const char *cp);
int inet_pton(int af, const char *src, void *dst);
const char *inet_ntop(int af, const void *src, char *dst, socklen_t cnt);
参考：http://beej.us/guide/bgnet/output/html/multipage/inet_ntopman.html
=============================================================
IPv4：
IP字符串 ——》 网络字节流
inet_addr、inet_network、inet_aton
程序代码：
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[*]#include <stdio.h>
[*]#include <stdlib.h>
[*]#include <unistd.h>
[*]#include <string.h>
[*]#include <netinet/in.h>
[*]#include <sys/socket.h>
[*]#include <sys/types.h>
[*]
[*]int main()
[*]{
[*] char ip[] = "192.168.0.74";
[*] long r1, r2, r3;//long
[*] struct in_addr addr;
[*]
[*] r1 = inet_addr(ip); //返回网络字节序
[*] if(-1 == r1){
[*] printf("inet_addr return -1/n");
[*] }else{
[*] printf("inet_addr ip: %ld/n", r1);
[*] }
[*]
[*] r2 = inet_network(ip); //返回主机字节序
[*] if(-1 == r2){
[*] printf("inet_addr return -1/n");
[*] }else{
[*] printf("inet_network ip: %ld/n", r2);
[*] printf("inet_network ip: %ld/n", ntohl(r2)); //ntohl: 主机字节序 ——> 网络字节序
[*] }
[*]
[*] r3 = inet_aton(ip, &addr);//返回网络字节序
[*] if(0 == r3){
[*] printf("inet_aton return -1/n");
[*] }else{
[*] printf("inet_aton ip: %ld/n", addr.s_addr);
[*] }
[*]
[*]/*****批量注释的一种方法*****/
[*]#if 0
[*] r3 = inet_aton(ip, addr);
[*] if(0 == r3){
[*] printf("inet_aton return -1/n");
[*] }else{
[*] printf("inet_aton ip: %ld/n", ntohl(addr.s_addr));
[*] }
[*]#endif
[*]
[*] return 0;
[*]}
运行结果：
$ gcc -W -o inet_addr inet_addr.c
$ ./inet_addr
inet_addr ip: 1241557184
inet_network ip: -1062731702
inet_network ip: 1241557184
inet_aton ip: 1241557184
--------------------------------------------------------------------------
IP字符串 《——》 网络字节流
inet_addr、inet_aton、inet_ntoa
程序代码：
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[*]#include <stdio.h>
[*]#include <sys/socket.h>
[*]#include <netinet/in.h>
[*]#include <arpa/inet.h>
[*]#include <string.h>
[*]int main(int argc, char *argv[])
[*]{
[*] char ip1[] = "192.168.0.74";
[*] char ip2[] = "211.100.21.179";
[*] struct in_addr addr1, addr2;
[*] long l1, l2;
[*] l1 = inet_addr(ip1); //IP字符串——》网络字节
[*] l2 = inet_addr(ip2);
[*] printf("IP1: %s/nIP2: %s/n", ip1, ip2);
[*] printf("Addr1: %ld/nAddr2: %ld/n", l1, l2);
[*]
[*] memcpy(&addr1, &l1, 4); //复制4个字节大小
[*] memcpy(&addr2, &l2, 4);
[*] printf("%s <--> %s/n", inet_ntoa(addr1), inet_ntoa(addr2)); //注意：printf函数自右向左求值、覆盖
[*] printf("%s/n", inet_ntoa(addr1)); //网络字节 ——》IP字符串
[*] printf("%s/n", inet_ntoa(addr2));
[*] return 0;
[*]}
运行结果：
$ gcc -W -o inet_ntoa inet_ntoa.c
$ ./inet_ntoa
IP1: 192.168.0.74
IP2: 211.100.21.179
Addr1: 1241557184
Addr2: 3004523731
192.168.0.74 <--> 192.168.0.74
192.168.0.74
211.100.21.179
=============================================================
IPv6：
IPv4 字符串 《——》网络字节流
inet_pton、inet_ntop
程序代码：
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[*]#include <stdio.h>
[*]#include <sys/types.h>
[*]#include <sys/socket.h>
[*]#include <arpa/inet.h>
[*]
[*]int main()
[*]{
[*] char ip[] = "192.168.0.74";
[*] struct in_addr addr;
[*]
[*] int ret = inet_pton(AF_INET, ip, (void *)&addr); //IP字符串 ——》网络字节流
[*] if(0 == ret){
[*] printf("inet_pton error, return 0/n");
[*] return -1;
[*] }else{
[*] printf("inet_pton ip: %ld/n", addr.s_addr);
[*] printf("inet_pton ip: 0x%x/n", addr.s_addr);
[*] }
[*]
[*] const char *pstr = inet_ntop(AF_INET, (void *)&addr, ip, 128);//网络字节流 ——》IP字符串
[*] if(NULL == pstr){
[*] printf("inet_ntop error, return NULL/n");
[*] return -1;
[*] }else{
[*] printf("inet_ntop ip: %s/n", ip);
[*] }
[*]
[*] return 0;
[*]}
运行结果：
$ gcc -W -o inet_ptoa inet_ptoa.c
$ ./inet_ptoa
inet_pton ip: 1241557184
inet_pton ip: 0x4a00a8c0
inet_ntop ip: 192.168.0.74
--------------------------------------------------------------------------
IPv6 字符串 《——》网络字节流
inet_pton、inet_ntop
程序代码：
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[*]#include <stdio.h>
[*]#include <stdlib.h>
[*]#include <string.h>
[*]#include <arpa/inet.h>
[*]
[*]int
[*]main(int argc, char **argv)
[*]{
[*] unsigned char buf[sizeof(struct in6_addr)];
[*] int domain, s;
[*] char str;
[*]
[*] if(argc != 3){
[*] fprintf(stderr, "usage: %s {i4|i6|<num>} string/n", argv);
[*] exit(EXIT_FAILURE);
[*] }
[*]
[*] domain = (strcmp(argv, "i4") == 0) ? AF_INET:(strcmp(argv, "i6") == 0) ? AF_INET6 : atoi(argv);
[*]
[*] //IP字符串 ——》网络字节流
[*] s = inet_pton(domain, argv, buf);
[*] if(s<=0){
[*] if(0 == s)
[*] fprintf(stderr, "Not in presentation format/n");
[*] else
[*] perror("inet_pton");
[*] exit(EXIT_FAILURE);
[*] }
[*]
[*] //网络字节流 ——》IP字符串
[*] if(inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL){
[*] perror("inet ntop/n");
[*] exit(EXIT_FAILURE);
[*] }
[*]
[*] printf("%s/n", str);
[*] exit(EXIT_SUCCESS);
[*]}
运行结果：
$ gcc -W -o inet_ptoa6 inet_ptoa6.c
$ ./inet_ptoa6 i6 0:0:0:0:0:FFFF:204.152.189.116
::ffff:204.152.189.116
$ ./inet_ptoa6 i4 204.152.189.116
204.152.189.116
参考：http://www.kernel.org/doc/man-pages/online/pages/man3/inet_pton.3.html
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