linux网络编程实例

获取服务器时间

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

#define HOSTNAMELEN 40
#define BUFLEN 1024
#define PORT 13

int main(int argc, char *argv[])
{
        int rc;
        int sockfd;
        char buf[BUFLEN+1];
        char *pc;
        struct sockaddr_in sa;
        struct hostent *hen;
        if (argc < 2) {
                fprintf(stderr, "missing host name\n");
                exit(1);
        }
        hen = gethostbyname(argv[1]);
        if (!hen) {
                perror("could not resolve host name");
                exit(1);
        }
        memset(&sa, 0, sizeof(sa));
        sa.sin_family = AF_INET;
        sa.sin_port = htons(PORT);
        memcpy(&sa.sin_addr.s_addr, hen->h_addr_list[0], hen->h_length);
        sockfd = socket(AF_INET, SOCK_STREAM, 0);
        if (sockfd < 0) {
                perror("socket()");
                exit(1);
        }
        rc = connect(sockfd, (struct sockaddr*)&sa, sizeof(sa));
        if (rc < 0) {
                perror("connect()");
                exit(1);
        }
        pc = buf;
        while (rc = read(sockfd, pc, BUFLEN - (pc-buf))) {
                pc += rc;
        }
        close(sockfd);
        *pc = ‘\0‘;
        printf("time: %s\n", buf);
        return 0;
}

tcp服务器端

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

#define PORT 8888
#define BACKLOG 1

int main()
{
        int listenfd, connfd;
        struct sockaddr_in servaddr;
        struct sockaddr_in cliaddr;
        int sin_size;
        //socket
        if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
                perror("socket()");
                exit(1);
        }
        //set socket can be reuse
        int opt = SO_REUSEADDR;
        setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
        //bind
        memset(&servaddr, 0, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
        servaddr.sin_port = htons(PORT);
        if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) == -1)
 {
                perror("bind()");
                exit(1);
        }
        //listen
        if (listen(listenfd, BACKLOG) == -1) {
                perror("listen()");
                exit(1);
        }
        //accept
        sin_size = sizeof(cliaddr);
        if ((connfd = accept(listenfd, (struct sockaddr*)&cliaddr, &sin_size)) =
= -1) {
                perror("accept()");
                exit(1);
        }
        //print client ip
        printf("get a connection from %s\n", inet_ntoa(cliaddr.sin_addr));
        //send
        char *msg = "welcome to server";
        send(connfd, msg, strlen(msg), 0);
        //close
        close(connfd);
        close(listenfd);

        return 0;
}

tcp客户端

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

#define PORT 8888
#define MAXDATASIZE 100

int main(int argc, char *argv[])
{
        int fd, numbytes;
        char buf[MAXDATASIZE];
        struct hostent *he;
        struct sockaddr_in servaddr;
        if (argc != 2) {
                printf("usage: %s <ip>\n", argv[0]);
                exit(1);
        }
        if ((he = gethostbyname(argv[1])) == NULL) {
                perror("gethostbyname()");
                exit(1);
        }
        if ((fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
                perror("socket()");
                exit(1);
        }
        bzero(&servaddr, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(PORT);
        servaddr.sin_addr = *((struct in_addr *)he->h_addr);
        if (connect(fd, (struct sockaddr*)&servaddr, sizeof(servaddr)) == -1) {
                perror("connect()");
                exit(1);
        }
        if ((numbytes = recv(fd, buf, MAXDATASIZE, 0)) == -1) {
                perror("recv()");
                exit(1);
        }
        buf[numbytes] = 0;
        printf("server message: %s\n", buf);
        close(fd);
        return 0;
}

udp服务器端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define PORT 8888
#define LINESIZE 100
int main()
{
        int sockfd;
        struct sockaddr_in servaddr;
        struct sockaddr_in cliaddr;
        int sin_size;
        int num;
        char msg[LINESIZE];
        if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
                perror("socket()");
                exit(1);
        }
        memset(&servaddr, 0, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
        servaddr.sin_port = htons(PORT);
        if (bind(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) == -1) {

                perror("bind()");
                exit(1);
        }
        sin_size = sizeof(cliaddr);
        while (1) {
                num = recvfrom(sockfd, msg, LINESIZE, 0,
                                (struct sockaddr*)&cliaddr, &sin_size);
                if (num < 0) {
                        perror("recvfrom()");
                        exit(1);
                }
                msg[num] = 0;
                printf("you got a message (%s) from %s\n", msg,
                                inet_ntoa(cliaddr.sin_addr));
                char *msg1 = "welcome to server.";
                sendto(sockfd, msg1, strlen(msg1), 0,
                                (struct sockaddr*)&cliaddr, sin_size);
                if (!strcmp(msg, "quit"))
                        break;
        }
        close(sockfd);
        return 0;
}

udp客户端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#define PORT 8888
#define LINESIZE 100
int main(int argc, char *argv[])
{
        int fd, numbytes;
        char buf[LINESIZE];
        struct hostent *he;
        struct sockaddr_in servaddr, reply;
        if (argc != 3) {
                printf("usage: %s <ip> <message>\n", argv[0]);
                exit(1);
        }
        if ((he = gethostbyname(argv[1])) == NULL) {
                perror("gethostbyname()");
                exit(1);
        }
        if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
                perror("socket()");
                exit(1);
        }
        bzero(&servaddr, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(PORT);
        servaddr.sin_addr = *((struct in_addr*)he->h_addr);
        sendto(fd, argv[2], strlen(argv[2]), 0,
                        (struct sockaddr*)&servaddr, sizeof(servaddr));
        while (1) {
                int len;
                if ((numbytes = recvfrom(fd, buf, LINESIZE, 0,
                                                (struct sockaddr*)&reply, &len))
 == -1) {
                        perror("recvfrom()");
                        exit(1);
                }
                if (len != sizeof(reply)
                                || memcmp((const void*)&servaddr, (const void*)&
reply, len) != 0) {
                        printf("receive message from other server.\n");
                        continue;
                }
                buf[numbytes] = 0;
                printf("server message: %s\n", buf);
                break;
        }
        close(fd);
        return 0;
}