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;
}