一、通信流程

       TCP:

   UDP:

   部分函数知识可以参考之前写的 Linux 网络编程——TCP

  TCP通信：

  客户端：

#include<stdio.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<stdlib.h>
#include<memory.h>
#include<string.h>


#define PORT 8888
int main(int argc,char **argv){
    int sock;
    struct sockaddr_in my_addr;
    int len;
    char buf[100];
    if(argc <3){
        printf("Usage: %s <ip> <port> <message>",argv[0]);
        exit(1);
    }

    if((sock=socket(AF_INET,SOCK_STREAM,0))<0){
        printf("socket create error!\n");
        exit(1);
    }
    my_addr.sin_family=AF_INET;
    my_addr.sin_port=htons(8888);
    if(inet_aton(argv[1],(struct in_addr *)&my_addr.sin_addr.s_addr) == 0){
        printf("%s chage error!\n",argv[1]);
        exit(1);
    }
    if(connect(sock,(struct sockaddr*)&my_addr,sizeof(struct sockaddr))<0){
        printf("connect error!\n");
        exit(1);
    }
    printf("connected!\n");

    while(1){
        memset(buf,0,100);
        len=recv(sock,buf,100,0);
        if(len<0){
            printf("recv error!\n");
            exit(1);
        }else if(len == 0){
            printf("the client quit!\n");
            exit(1);
        }else{
            printf("receive message: %s \n",buf);
        }
        printf("-------------------------\n");
        memset(buf,0,100);
        printf("Input message to send: ");
        fgets(buf,100,stdin);
        len=send(sock,buf,strlen(buf)-1,0);
        if(len<0){
            printf("send error!\n");
            exit(1);
        }else{
            printf("send succeed! send : %s\n",buf);
        }
    }
    close(sock);
}

  服务端：

#include<stdio.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<stdlib.h>
#include<memory.h>
#include<string.h>
#include<sys/socket.h>

#define PORT 8888
int main(){
    int sock,new_sock;
    struct sockaddr_in my_addr,client_addr;
    int len;
    char buf[100];

    if((sock=socket(AF_INET,SOCK_STREAM,0))<0){
        printf("socket create error!\n");
        exit(1);
    }
    memset(&my_addr,0,sizeof(my_addr));
    my_addr.sin_family=AF_INET;
    my_addr.sin_port=htons(PORT);
    my_addr.sin_addr.s_addr=INADDR_ANY;

    if(bind(sock,(struct sockaddr*)&my_addr,sizeof(my_addr))==-1){
        printf("bind error!\n");
        exit(1);
    }
    if(listen(sock,5)<0){
        printf("listen error!\n");
        exit(1);
    }
    len=sizeof(struct sockaddr);
    if((new_sock=accept(sock,(struct sockaddr*)&client_addr,&len))<0){
        printf("accept error!\n");
        exit(1);
    }else{
        printf("server: get connection from %s,port %d socket %d \n",inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port),new_sock);

    }
    while(1){
        memset(buf,0,100);
        printf("Input message to send: ");
        fgets(buf,100,stdin);
        if(!strncasecmp(buf,"quit",4)){
            printf("server is closing...\n");
            break;
        }
        len=send(new_sock,buf,strlen(buf)-1,0);
        if(len<0){
            printf("send error!\n");
            exit(1);
        }else{
            printf("send succeed! send : %s\n",buf);
        }
        printf("------------------------------\n");
        memset(buf,0,100);
        len=recv(new_sock,buf,100,0);
        if(len<0){
            printf("recv error!\n");
            exit(1);
        }else if(len == 0){
            printf("the client quit!\n");
            break;
        }else{
            printf("receive message: %s \n",buf);
        }
    }
    close(sock);
    close(new_sock);
}
         

         相对于TCP来说UDP就要简单写，毕竟步骤少嘛：

     服务端 ：

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

int main(int argc, char **argv){
	struct sockaddr_in s_addr,c_addr;
	int sock;
	socklen_t addr_len;
	int len;
	char buff[128];

	if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
		perror("socket");
		exit(errno);
	} else
		printf("create socket.\n\r");

	memset(&s_addr, 0, sizeof(struct sockaddr_in));

	s_addr.sin_family = AF_INET;
	s_addr.sin_port = htons(7838);
	s_addr.sin_addr.s_addr = INADDR_ANY;

	if ((bind(sock, (struct sockaddr *) &s_addr, sizeof(s_addr))) == -1) {
		perror("bind");
		exit(errno);
	} else
		printf("bind address to socket.\n\r");

	addr_len = sizeof(c_addr);
	while (1) {
                  memset(buff,0,sizeof(buff));
                  //第三个参数标识为0，第四个参数为信息来源主机地址信息
		len = recvfrom(sock, buff, sizeof(buff) - 1, 0, (struct sockaddr *) &c_addr, &addr_len);
		if (len < 0) {
			perror("recvfrom");
			exit(errno);
		}

		buff[len] = '\0';
		printf("recive come from %s:%d message:%s\n\r",inet_ntoa(c_addr.sin_addr), ntohs(c_addr.sin_port), buff);
	}
	return 0;
}

     客户端：

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

int main(int argc, char **argv){
    struct sockaddr_in s_addr;
    int sock;
    int addr_len;
    int len;
    char buff[128];

    if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
        perror("socket");
        exit(errno);
    } else
        printf("create socket.\n\r");

    s_addr.sin_family = AF_INET;
    s_addr.sin_port = htons(7838);
    if (argc>2){
        s_addr.sin_addr.s_addr = inet_addr(argv[1]);
        strcpy(buff,argv[2]);
    }
    else {
        printf("input sever ip!\n");
        exit(0);
    }

    addr_len = sizeof(s_addr);
    len = sendto(sock, buff, strlen(buff), 0, (struct sockaddr *) &s_addr, addr_len);
    if (len < 0) {
        printf("\n\rsend error.\n\r");
        return 3;
    }

    printf("send success.\n\r");
    return 0;
}

    本篇博客出自  阿修罗道，转载请注明出处：http://blog.csdn.net/fansongy/article/details/6896851