Linux编程获取本机IP地址的几种方法

在进行Linux网络编程时,经常会需要获取本机IP地址,除了常规的读取配置文件外,本文罗列几种个人所知的编程常用方法,仅供参考,如有错误请指出。

方法一:使用ioctl()获取本地IP地址 

Linux下可以使用ioctl()函数以及结构体 struct ifreq和结构体struct ifconf来获取网络接口的各种信息。具体过程是先通过ictol获取本地所有接口的信息保存到ifconf结构中,再从其中取出每个ifreq表示的接口信息。

如果本机的IP地址绑定在第一块网卡上,则只需指定网卡名称,无需获取所有网卡的信息即可获取,见如下函数:

int get_localip(const char * eth_name, char *local_ip_addr)
{
	int ret = -1;
    register int fd;
    struct ifreq ifr;

	if (local_ip_addr == NULL || eth_name == NULL)
	{
		return ret;
	}
	if ((fd=socket(AF_INET, SOCK_DGRAM, 0)) > 0)
	{
		strcpy(ifr.ifr_name, eth_name);
		if (!(ioctl(fd, SIOCGIFADDR, &ifr)))
		{
			ret = 0;
			strcpy(local_ip_addr, inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr));
		}
	}
	if (fd > 0)
	{
		close(fd);
	}
    return ret;
}

如果想通过获取所有网络接口信息,示例代码如下:

#include 
#include 
#include 
#include 
#include 
#include 
#include 

int get_localip(const char * eth_name, char *local_ip_addr)
{
	int ret = -1;
    register int fd, intrface;
    struct ifreq ifr[32];
    struct ifconf ifc;

    if (local_ip_addr == NULL || eth_name == NULL)
	{
        return ret;
	}
	if ((fd=socket(AF_INET, SOCK_DGRAM, 0)) > 0)
	{
		ifc.ifc_len = sizeof ifr;
		ifc.ifc_buf = (caddr_t)ifr;
		if (!ioctl(fd, SIOCGIFCONF, (char*)&ifc)) //获取所有接口信息
		{
			intrface = ifc.ifc_len / sizeof(struct ifreq);
			while (intrface-- > 0)
			{
				//Get IP Address
				if (!(ioctl(fd, SIOCGIFADDR, (char*)&ifr[intrface])))
				{
					if(strcmp(eth_name, ifr[intrface].ifr_name) == 0)
					{
						ret = 0;
						sprintf(local_ip_addr, "%s", inet_ntoa(((struct sockaddr_in*)(&ifr[intrface].ifr_addr))->sin_addr));
						break;
					}
				}
			}
		}
	}
	if (fd > 0)
	{
		close(fd);
	}
    return ret;
}

int main(int argc, const char **argv)
{
	int ret;
	char local_ip[20] = {0};

	ret = get_localip("eth0", local_ip);
	if (ret == 0)
	{
		printf("local ip:%s\n", local_ip);
	}
	else
	{
		printf("get local ip failure\n");
	}
	return 0;
}

方法二:getsockname()获取本地IP地址 

getsockname()用于获取一个已捆绑已连接套接字的本地地址。若一个套接字与INADDR_ANY捆绑,也就是说该套接字可以用任意主机的地址,此时除非调用connect()或accept()来连接,否则getsockname()将不会返回主机IP地址的任何信息。

示例代码:

#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define PORT 80
#define SERVER_IP "14.215.177.38"

int main(int argc, const char **argv)
{
	int ret = -1;
    socklen_t len;
    char buf[30] = {0};
    struct sockaddr_in server_addr, local_addr;
    int fd = socket(AF_INET, SOCK_STREAM, 0);
	//int fd = socket(AF_INET, SOCK_DGRAM, 0);
	if (fd <= 0)
    {
	    printf("fail to creat socket\n");
        return -1;
    }

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port   = htons(PORT);
	server_addr.sin_addr.s_addr = inet_addr(SERVER_IP);
    if(connect(fd, (struct sockaddr*)&server_addr, sizeof(server_addr))<0)
    {
        printf("connect error!!!\n");
        goto end;
    }
	len = sizeof(local_addr);
    memset(&local_addr,  0, sizeof(local_addr));
    ret = getsockname(fd, (struct sockaddr*)&local_addr, &len);
	if (ret == 0)
	{
		printf("local ip is %s, local port is %d\n", inet_ntop(AF_INET, &local_addr.sin_addr, buf, sizeof(buf)), ntohs(local_addr.sin_port));
	}
	else
	{
		printf("getsockname failed, error=%d\n", errno);
	}

end:
	if (fd)
	{
		close(fd);
	}
    return ret;
}

方法三:getaddrinfo()获取本地IP地址

getaddrinfo()可以完成网络主机中主机名和服务名到地址的映射,但是一般不能用来获取本地IP地址,当它用来获取本地IP地址时,返回的一般是127.0.0.1本地回环地址,且该函数仅仅支持IPv4。

示例代码:

#include 
#include 
#include 
#include 

// 获取本地IP时,一般都是127.0.0.1
int main(int argc, const char **argv)
{
	int ret;
    char host_name[128] = {0};
    struct addrinfo *res, *cur;
    struct sockaddr_in *addr;

    if (gethostname(host_name, sizeof(host_name)) < 0)
    {
	    printf("gethostname error\n");
	    return -1;
    }
    ret = getaddrinfo(host_name, NULL, NULL, &res);
	if (ret != 0)
	{
		printf("Error: error in getaddrinfo on hostname: %s\n", gai_strerror(ret));
		return -1;
	}
    for(cur = res; cur != NULL; cur = cur->ai_next)
    {
        if(cur->ai_family == AF_INET)
        {
            addr = (struct sockaddr_in*)cur->ai_addr;
			printf("local ip:%s\n", inet_ntoa(addr->sin_addr));
        }
		//char host[1024] = {0};
		//ret = getnameinfo(cur->ai_addr, cur->ai_addrlen, host, sizeof(host), NULL, 0, NI_NUMERICHOST);
		//if(ret != 0)
		//{
		//	printf("getnameinfo: %s\n", gai_strerror(ret));
		//}
		//else
		//{
		//	printf("ip: %s\n", host);
		//}
    }
	freeaddrinfo(res);
    return 0;
}

方法四:gethostbyname ()获取本地IP地址

gethostbyname()和getaddrinfo()的功能类似,一般用于通过主机名或者服务名,比如域名来获取主机的IP地址。但是要想获取本地IP地址的时候,一般获取的是回环地址127.0.0.1。

示例代码:

#include 
#include 
#include 
#include 

// 获取本地IP时,一般都是127.0.0.1
int main(int argc, const char **argv)
{
	int i = 0;
    char host_name[128] = {0};
    struct hostent *hptr;

    if (gethostname(host_name, sizeof(host_name)) < 0)
	{
		printf("gethostname error\n");
		return -1;
	}
    if ((hptr=gethostbyname(host_name)) == NULL)
	{
		printf("gethostbyname error\n");
		return -1;
	}
	while(hptr->h_addr_list[i] != NULL)
	{
		printf("hostname: %s\n", hptr->h_name);
		printf("      ip: %s\n", inet_ntoa(*(struct in_addr*)hptr->h_addr_list[i]));
		i++;
	}
    return 0;
}

方法五:通过getifaddrs()获取本地IP地址

/*代码来自StackOverflow:

http://stackoverflow.com/questions/212528/linux-c-get-the-ip-address-of-local-computer */

示例代码:

#include 
#include 
#include 
#include 
#include 
#include 

int main (int argc, const char * argv[])
{
    struct ifaddrs * ifAddrStruct=NULL;
    struct ifaddrs * ifa=NULL;
    void * tmpAddrPtr=NULL;

    getifaddrs(&ifAddrStruct);

    for (ifa = ifAddrStruct; ifa != NULL; ifa = ifa->ifa_next)
	{
        if (!ifa->ifa_addr)
		{
            continue;
        }
        if (ifa->ifa_addr->sa_family == AF_INET) // check it is IP4
		{
            // is a valid IP4 Address
            tmpAddrPtr=&((struct sockaddr_in *)ifa->ifa_addr)->sin_addr;
            char addressBuffer[INET_ADDRSTRLEN];
            inet_ntop(AF_INET, tmpAddrPtr, addressBuffer, INET_ADDRSTRLEN);
            printf("%s IP Address %s\n", ifa->ifa_name, addressBuffer);
        }
		else if (ifa->ifa_addr->sa_family == AF_INET6) // check it is IP6
		{
            // is a valid IP6 Address
            tmpAddrPtr=&((struct sockaddr_in6 *)ifa->ifa_addr)->sin6_addr;
            char addressBuffer[INET6_ADDRSTRLEN];
            inet_ntop(AF_INET6, tmpAddrPtr, addressBuffer, INET6_ADDRSTRLEN);
            printf("%s IP Address %s\n", ifa->ifa_name, addressBuffer);
        }
    }
    if (ifAddrStruct!=NULL)
	{
		freeifaddrs(ifAddrStruct);
	}

    return 0;
}

方法六:通过popen()调用ifconfig获取本地IP地址

用popen()建立一个管道,管道的一端执行命令ifconfig,管道的另一端读取收到的数据并进行相应的解析。这种方法需要执行shell命令,配合正则表达式,效率较低,一般不采用。而这种方式其实更倾向于配置,原因就是使用简单。

示例代码:

#include 
#include 

#define ETH_NAME	"ens33"

int main(int argc, const char *argv[])
{
	FILE *fp;
	char buf[256] = {0};
	char command[256] = {0};
	//char *fmt = "ifconfig %s|sed -n '2p'|sed -n 's#^.*dr:##gp'|sed -n 's#B.*$##gp'";
	char *fmt = "ifconfig %s|grep 'inet addr'|awk '{ print $2}' | awk -F: '{print $2}'";

	snprintf(command, sizeof(command), fmt, ETH_NAME);
	if((fp = popen(command, "r")) == NULL)
	{
		perror("Fail to popen\n");
		return -1;
	}
	while(fgets(buf, sizeof(buf), fp) != NULL)
	{
		printf("%s", buf);
	}

	pclose(fp);
	return 0;
}

参考文献

[1]https://blog.csdn.net/bailyzheng/article/details/7489656

[2]https://blog.csdn.net/k346k346/article/details/48231933

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