显示客户端本机的IP地址和端口

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>

const int maxline=4096;

int main(int argc, char **argv) {
	int sockfd, n;
	char recvline[maxline+1], errbuff[maxline];
	struct sockaddr_in servaddr, localaddr;
	socklen_t len=sizeof(localaddr);

	if(argc != 2) {
		fprintf(stderr, "usage: a.out <IPaddress>\n");
		exit(-1);
	}

	if((sockfd=socket(AF_INET, SOCK_STREAM, 0))<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "socket error: %s\n", errbuff);
		exit(-1);
	}

	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family=AF_INET;
	servaddr.sin_port=htons(9999);
	if(inet_pton(AF_INET, argv[1], &servaddr.sin_addr)<=0) {
		fprintf(stderr, "inet_pton error for %s\n", argv[1]);
		exit(-1);
	}

	if(connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr))<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "connect error: %s\n", errbuff);
		exit(-1);
	}

	if(getsockname(sockfd, (struct sockaddr *)&localaddr, &len)<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "connect error: %s\n", errbuff);
		exit(-1);
	}
	printf("local ip: %s, local port: %d\n", inet_ntop(AF_INET, &localaddr.sin_addr, errbuff, sizeof(errbuff)), ntohs(localaddr.sin_port));

	while((n=read(sockfd, recvline, maxline))>0) {
		recvline[n]=0;
		if(fputs(recvline, stdout)==EOF) {
			fprintf(stderr, "fputs error\n");
			exit(-1);
		}
	}
	if(n<0) {
		fprintf(stderr, "read error.\n");
		exit(-1);
	}
	
	return 0;
}