简单服务器

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

int main(){
    // 创建服务端fd
    int listenfd = socket(AF_INET,SOCK_STREAM, IPPROTO_TCP);
    if(listenfd < 0){
        printf("socket error");
        return -1;
    }

    // 创建IP地址
    struct sockaddr_in svraddr;/*声明一个变量，类型为协议地址类型*/
    svraddr.sin_family = AF_INET;/*使用IPv4协议*/
    svraddr.sin_port = htons(8887);/*监听8887端口*/
    svraddr.sin_addr.s_addr = htonl(INADDR_ANY);/*绑定本机IP，使用宏定义绑定*/

    // 服务端fd和ip地址绑定
    if(bind(listenfd ,(struct sockaddr *)&svraddr,sizeof(svraddr)) < 0){
        printf("bind error");
        return -1;
    }

    // 上面创建和客户端一样，closed状态，当调用listen后从closed状态转listen
    if(listen(listenfd, 20) < 0){
        printf("listen error");
        return -1;
    }

    // 下面是客户端socket
    struct sockaddr_in cliaddr;/*只是声明，并没有赋值*/
    memset(&cliaddr, 0, sizeof(cliaddr));
    socklen_t ret = sizeof(cliaddr);
    // accept会阻塞进程
    // 客户端生成的fd，通过给客户端fd写入内容就会发送到客户端
    int sockfd= accept(listenfd, (struct sockaddr*)&cliaddr, &ret);
    if(sockfd < 0){
        printf("appect error");
        return -1;
    }

    char str[] = "Hello World";
    write(sockfd , str, sizeof(str));

    close(sockfd);
    close(listenfd);
}

客户端代码

#include <stdio.h>
#include <netinet/in.h>
#include <sys/socket.h>
int main()
{
    int sockfd= socket(AF_INET,SOCK_STREAM, IPPROTO_TCP);

    if(sockfd== -1){
        printf("socket error");
        return -1;
    }

    struct sockaddr_in svraddr;
    svraddr.sin_family = AF_INET;/*使用IPv4协议*/
    svraddr.sin_port = htons(8887);/*需要连接的远程服务器端口*/
    svraddr.sin_addr.s_addr = inet_addr("127.0.0.1");/*需要连接的远程服务器IP*/

    if(connect(sockfd, (struct sockaddr *)&svraddr, sizeof(servaddr))  < 0){
        printf("connect error");
        return -1;
    }

    char str[64];
    read(sockfd, str, 64);
    printf(str);

    close(sockfd);
}

多进程服务器

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

void doit(int sockfd);

int main()
{
    int listenfd= socket(AF_INET,SOCK_STREAM, IPPROTO_TCP);
    pid_t pid;

    if(listenfd < 0){
        printf("socket error");
        return -1;
    }

    struct sockaddr_in svraddr;/*声明一个变量，类型为协议地址类型*/
    svraddr.sin_family = AF_INET;/*使用IPv4协议*/
    svraddr.sin_port = htons(8887);/*监听8887端口*/
    svraddr.sin_addr.s_addr = htonl(INADDR_ANY);/*绑定本机IP，使用宏定义绑定*/

    if(bind(listenfd,(struct sockaddr *)&svraddr,sizeof(svraddr)) < 0){
        printf("bind error");
        return -1;
    }

    if(listen(listenfd, 20) < 0){
        printf("listen error");
        return -1;
    }

    for( ; ; ){   /*while(1){} */
        struct sockaddr_in cliaddr;/*只是声明，并没有赋值*/
        socklen_t cliaddr_size = sizeof(cliaddr);
        int sockfd= accept(listenfd, (struct sockaddr*)&cliaddr, &cliaddr_size );

        if(sockfd < 0){
            printf("appect error");
            return -1;
        }

        if( (pid = fork()) == 0 ){
            close(listenfd);/*子进程不需要监听，关闭*/
            doit(sockfd);/*针对已连接的客户端套接字进行读写*/
            close(sockfd);/*处理完毕，关闭客户端连接*/
            exit(0);/*自觉退出*/
        }

        close(sockfd);
        /*close(listenfd);*/
    }
}

void doit(int sockfd){
    char str[] = "Hello World";
    sleep(3);//3秒之后再向客户端发送数据
    write(sockfd, str, sizeof(str));
}

多线程服务

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

#define IP "192.168.102.175"
#define PORT 7000

void print_err(char *str, int line, int err_no) {
	printf("%d, %s :%s\n",line,str,strerror(err_no));
	_exit(-1);
}

/*子线程中先接收从客户端发来的消息，再发送一个消息给客户端*/
void *receive(void *pth_arg) {
	int ret = 0;
	long cfd = (long)pth_arg;
	char buf[100] = {0};
	while(1) {
		bzero(&buf, sizeof(buf));
		ret = recv(cfd, &buf, sizeof(buf),0);	
		if (-1 == ret) {
			print_err("recv failed",__LINE__,errno);
		}
		else if (ret > 0)
			printf("recv from client %s \n",buf);
		ret = send(cfd,"recv ok\n", sizeof("recv ok\n"), 0);
		if (-1 == ret) print_err("send failed", __LINE__, errno);
	}
}

int main()
{
	int skfd = -1, ret = -1;
	skfd = socket(AF_INET, SOCK_STREAM, 0);
	if ( -1 == skfd) {
		print_err("socket failed",__LINE__,errno);
	}

	struct sockaddr_in addr;
	addr.sin_family = AF_INET; //设置tcp协议族
	addr.sin_port = htons(PORT); //设置端口号
	addr.sin_addr.s_addr = inet_addr(IP); //设置ip地址

	ret = bind(skfd, (struct sockaddr*)&addr, sizeof(addr));
	if ( -1 == ret) {
		print_err("bind failed",__LINE__,errno);
	}
 
	ret = listen(skfd, 3);
	if ( -1 == ret ) {
		print_err("listen failed", __LINE__, errno);
	}
	
	//使用accept阻塞形式得监听客户端的发来的连接，并返回通信描述符
	long cfd = -1;
	pthread_t id;
	while (1) {
		struct sockaddr_in caddr = {0};
		int csize = sizeof(caddr);
		cfd = accept(skfd, (struct sockaddr*)&caddr, &csize);
		if (-1 == cfd) {
			print_err("accept failed", __LINE__, errno);
		}
		//建立连接后打印一下客户端的ip和端口号
		printf("cport = %d, caddr = %s\n", ntohs(caddr.sin_port),inet_ntoa(caddr.sin_addr));
	
		//使用accept返回到描述符，创建子线程进行数据传输
		int ret = pthread_create(&id,NULL,receive,(void*)cfd);
		if(-1 == ret) print_err("accept failed", __LINE__, errno); 
	}
	return 0;
}