客户端代码

client.cpp

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

int main() {

	//创建一个socket
	int sock_fd = socket(AF_INET, SOCK_STREAM, 0);

	//创建好地址
	struct sockaddr_in address;
	address.sin_family = AF_INET;
	address.sin_port = htons(1991); //端口和服务器端对应
	address.sin_addr.s_addr = inet_addr("127.0.0.1");

	//开始连接服务器
	int result = connect(sock_fd, (struct sockaddr *) &address, sizeof(address));

	if(result == -1){
		perror("connect failed: ");
		exit(1);
	}

	char ch = 'A';
	//给服务器发送 一个字符
	write( sock_fd, &ch, 1);
	printf("client says: %c\n", ch);

	// 读取一个字符
	read(sock_fd, &ch, 1);
	printf("get char from server:%c\n", ch);

	//关掉连接
	close(sock_fd);


	return 0;
}

服务器端

server.cpp

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

int main() {

	//用 SOCK_STREAM 标识建立 TCP连接
	int sockfd = socket(AF_INET, SOCK_STREAM, 0);

	struct sockaddr_in server_addr;
	server_addr.sin_family = AF_INET;
	server_addr.sin_port = htons(1991); //需要转化字节序

	//需要把点分10进制的地址转化
	/*
	 * Name: inet_addr
	 Prototype: uint32_t inet_addr (const char *name)
	 Description:
	 This function converts the IPv4 Internet host address name from the standard numbers-and-dots notation
	 into binary data. If the input is not valid, inet_addr returns INADDR_NONE. This is an obsolete interface to
	 inet_aton, described immediately above. It is obsolete because INADDR_NONE is a valid address
	 (255.255.255.255), and inet_aton provides a cleaner way to indicate error return.
	 */
	server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

	/*绑定*/
	bind(sockfd, (struct sockaddr *) &server_addr, sizeof(server_addr));

	/*
	 * Name: listen
	 Prototype: int listen (int socket, int n)
	 Description:
	 The listen function enables the socket socket to accept connections, thus making it a server socket.

	 The argument n specifies the length of the queue for pending connections. When the queue fills, new
	 clients attempting to connect fail with ECONNREFUSED until the server calls accept to accept a
	 connection from the queue.

	 The listen function returns 0 on success and -1 on failure. The following errno error conditions are defined
	 for this function:
	 */
	listen(sockfd, 10);

	char ch;

	struct sockaddr_in client_addr;
	socklen_t len = sizeof(client_addr);
//	socklen_t len = 0;
	while(1)
	{
		int client_sockfd;
		printf("server waiting: \n");
		client_sockfd = accept(sockfd, (struct sockaddr *) &client_addr, &len);

		//只读取一个字符
		read(client_sockfd, &ch, 1);
		printf("get char from client: %c\n", ch);
		++ch;

		//把该字符 +1后再发回给客户端
		write(client_sockfd, &ch, 1);

		close(client_sockfd);
	}

	//printf("%0x", server_addr.sin_addr.s_addr);
	return 0;
}