Linux系统 C++ 获取网络接口，以及主机网关IP

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Linux系统 C++ 获取网络接口，以及主机网关IP，完整的C++源码如下：

#include <arpa/inet.h> //for in_addr

#include <linux/rtnetlink.h> //for rtnetlink

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#include <net/if.h> //for IF_NAMESIZ, route_info

#include <stdio.h>

#include <stdlib.h> //for malloc(), free()

#include <string.h> //for strstr(), memset()

#include <string>

using namespace std;

#define BUFSIZE 8192

struct route_info

{

u_int dstAddr;

u_int srcAddr;

u_int gateWay;

char ifName[IF_NAMESIZE];

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};

int readNlSock(int sockFd, char *bufPtr, int seqNum, int pId)

{

struct nlmsghdr *nlHdr;

int readLen = 0, msgLen = 0;

do{

//收到内核的应答

if((readLen = recv(sockFd, bufPtr, BUFSIZE - msgLen, 0)) < 0)

{

perror("SOCK READ: ");

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return -1;

}

nlHdr = (struct nlmsghdr *)bufPtr;

//检查header是否有效

if((NLMSG_OK(nlHdr, readLen) == 0) || (nlHdr->nlmsg_type == NLMSG_ERROR))

{

perror("Error in recieved packet");

return -1;

}

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if(nlHdr->nlmsg_type == NLMSG_DONE)

{

break;

}

else

{

bufPtr += readLen;

msgLen += readLen;

}

if((nlHdr->nlmsg_flags & NLM_F_MULTI) == 0)

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{

break;

}

} while((nlHdr->nlmsg_seq != seqNum) || (nlHdr->nlmsg_pid != pId));

return msgLen;

}

//分析返回的路由信息

void parseRoutes(struct nlmsghdr *nlHdr, struct route_info *rtInfo,char *gateway, char *ifName)

{

struct rtmsg *rtMsg;

struct rtattr *rtAttr;

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int rtLen;

char *tempBuf = NULL;

struct in_addr dst;

struct in_addr gate;

tempBuf = (char *)malloc(100);

rtMsg = (struct rtmsg *)NLMSG_DATA(nlHdr);

// If the route is not for AF_INET or does not belong to main routing table

//then return.

if((rtMsg->rtm_family != AF_INET) || (rtMsg->rtm_table != RT_TABLE_MAIN))

return;

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rtAttr = (struct rtattr *)RTM_RTA(rtMsg);

rtLen = RTM_PAYLOAD(nlHdr);

for(;RTA_OK(rtAttr,rtLen);rtAttr = RTA_NEXT(rtAttr,rtLen)){

switch(rtAttr->rta_type) {

case RTA_OIF:

if_indextoname(*(int *)RTA_DATA(rtAttr), rtInfo->ifName);

break;

case RTA_GATEWAY:

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rtInfo->gateWay = *(u_int *)RTA_DATA(rtAttr);

break;

case RTA_PREFSRC:

rtInfo->srcAddr = *(u_int *)RTA_DATA(rtAttr);

break;

case RTA_DST:

rtInfo->dstAddr = *(u_int *)RTA_DATA(rtAttr);

break;

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}

dst.s_addr = rtInfo->dstAddr;

if (strstr((char *)inet_ntoa(dst), "0.0.0.0"))

{

sprintf(ifName, "%s", rtInfo->ifName);

//printf("oif:%s",rtInfo->ifName);

gate.s_addr = rtInfo->gateWay;

sprintf(gateway, "%s", (char *)inet_ntoa(gate));

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//printf("%sn",gateway);

gate.s_addr = rtInfo->srcAddr;

//printf("src:%sn",(char *)inet_ntoa(gate));

gate.s_addr = rtInfo->dstAddr;

//printf("dst:%sn",(char *)inet_ntoa(gate));

}

free(tempBuf);

return;

}

int get_gateway(char *gateway, char *ifName)

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{

struct nlmsghdr *nlMsg;

struct rtmsg *rtMsg;

struct route_info *rtInfo;

char msgBuf[BUFSIZE];

int sock, len, msgSeq = 0;

if((sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)) < 0)

{

perror("Socket Creation: ");

return -1;

}

memset(msgBuf, 0, BUFSIZE);

nlMsg = (struct nlmsghdr *)msgBuf;

rtMsg = (struct rtmsg *)NLMSG_DATA(nlMsg);

nlMsg->nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg)); // Length of message.

nlMsg->nlmsg_type = RTM_GETROUTE; // Get the routes from kernel routing table .

nlMsg->nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST; // The message is a request for dump.

nlMsg->nlmsg_seq = msgSeq++; // Sequence of the message packet.

nlMsg->nlmsg_pid = getpid(); // PID of process sending the request.

if(send(sock, nlMsg, nlMsg->nlmsg_len, 0) < 0){

printf("Write To Socket Failed…n");

return -1;

}

if((len = readNlSock(sock, msgBuf, msgSeq, getpid())) < 0) {

printf("Read From Socket Failed…n");

return -1;

}

rtInfo = (struct route_info *)malloc(sizeof(struct route_info));

for(;NLMSG_OK(nlMsg,len);nlMsg = NLMSG_NEXT(nlMsg,len)){

memset(rtInfo, 0, sizeof(struct route_info));

parseRoutes(nlMsg, rtInfo, gateway, ifName);

}

free(rtInfo);

close(sock);

return 0;

}

int main()

{

char buff[256], ifName[12];

get_gateway(buff, ifName);

printf("interface:%sngetway: %sn",ifName, buff);

return 0;

}

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