套接字编程：在C中向不同的客户端发送和接收不同的数据

Question

我已经使用 TCP/IP 协议在 c 套接字编程中编写了基本的客户端服务器代码，但我无法弄清楚如何使其连接到不同的客户端并作为客户端的函数向它们发送/接收不同的数据（这意味着如果是第一个客户端向他发送该数据，如果是该客户端向他发送其他数据）等等。

这是我发现的唯一结果是将相同的数据发送到不同的客户端。

当前服务器：

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

#include <netinet/in.h>

int main() {

  char server_message[100] = {0};
  int server_socket = 0;
  int client_socket = 0;

  struct sockaddr_in server_address;  

  server_socket = socket(AF_INET, SOCK_STREAM, 0);

  server_address.sin_family = AF_INET;
  server_address.sin_port = htons(9002);
  server_address.sin_addr.s_addr = INADDR_ANY;

  // bind the socket to our specified IP and port
  bind(server_socket, (struct sockaddr*) &server_address, sizeof(server_address));

  listen(server_socket, 2);

  client_socket = accept(server_socket, NULL, NULL);

  printf("Please enter a massage:");
  fgets(server_message, 100, stdin);

  send(client_socket, server_message, sizeof(server_message), 0);

  close(server_socket);
  return 0;
}

Answer 1

通过使用来自geeksforgeeks的原始代码和Myst评论我们可以解决它。

您有一台在本地主机 127.0.0.1 上提供服务的服务器，并且可以有多个客户端，在此示例中我假设 5 个客户端就足够了。

运行一次服务器，然后运行多个客户端以分别连接到该服务器。

服务器.c

// Server side C/C++ program to demonstrate Socket programming 
#include <unistd.h> 
#include <stdio.h> 
#include <sys/socket.h> 
#include <stdlib.h> 
#include <netinet/in.h> 
#include <string.h> 
#define PORT 8080 
#define STRING_SIZE 100
#define BUFFER_SIZE 100

int main(int argc, char const *argv[]) 
{
     
    int server_fd, new_socket[5], valread; 
    struct sockaddr_in address; 
    int opt = 1; 
    int addrlen = sizeof(address); 
    char buffer[1024] = {0}; 
    
    char *hello = "Hello from server";
    
    // Creating socket file descriptor 
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) 
    { 
        perror("socket failed"); 
        exit(EXIT_FAILURE); 
    } 
    
    // Forcefully attaching socket to the port 8080 
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, 
                                                &opt, sizeof(opt))) 
    { 
        perror("setsockopt"); 
        exit(EXIT_FAILURE); 
    } 
    address.sin_family = AF_INET; 
    address.sin_addr.s_addr = INADDR_ANY; 
    address.sin_port = htons( PORT ); 
    
    // Forcefully attaching socket to the port 8080 
    if (bind(server_fd, (struct sockaddr *)&address, 
                                sizeof(address))<0) 
    { 
        perror("bind failed"); 
        exit(EXIT_FAILURE); 
    } 
    if (listen(server_fd, 3) < 0) 
    { 
        perror("listen"); 
        exit(EXIT_FAILURE); 
    }
     
    for (int i=0;i<5;i++){ 
        if ((new_socket[i] = accept(server_fd, (struct sockaddr *)&address, 
                        (socklen_t*)&addrlen))<0) 
        { 
            perror("accept"); 
            exit(EXIT_FAILURE); 
        } 
    valread = read(new_socket[i], buffer, 1024); 
    printf("%s\n", buffer);
    
    char send_buf[STRING_SIZE] = "hello";
    char buf[BUFFER_SIZE]={0};
    sprintf(buf, "%d", i);
    strcat(send_buf, buf);

    send(new_socket[i], send_buf, strlen(send_buf), 0); 
    //printf("Hello message sent\n"); 
    
    }
    
    return 0; 
} 

客户端.c

// Client side C/C++ program to demonstrate Socket programming 
#include <stdio.h> 
#include <sys/socket.h> 
#include <arpa/inet.h> 
#include <unistd.h> 
#include <string.h> 
#define PORT 8080 

int main(int argc, char const *argv[]) 
{ 
    int sock = 0, valread; 
    struct sockaddr_in serv_addr; 
    char *hello = "Hello from client"; 
    char buffer[1024] = {0}; 
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) 
    { 
        printf("\n Socket creation error \n"); 
        return -1; 
    } 

    serv_addr.sin_family = AF_INET; 
    serv_addr.sin_port = htons(PORT); 
    
    // Convert IPv4 and IPv6 addresses from text to binary form 
    if(inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr)<=0) 
    { 
        printf("\nInvalid address/ Address not supported \n"); 
        return -1; 
    } 

    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) 
    { 
        printf("\nConnection Failed \n"); 
        return -1; 
    }
     
    send(sock , hello , strlen(hello) , 0 ); 
    //printf("Hello message sent\n"); 
    valread = read( sock , buffer, 1024); 
    printf("%s\n", buffer); 
    
    return 0; 
} 

奔跑

使用

gcc client.c -o client

和

gcc server.c -o server

编译代码后

为服务器打开一个终端并通过运行

./server

启动服务器。

现在您可以通过运行

./client

将多个客户端 [最多 5] 连接到它。

编辑

感谢 anonymouse 评论，用这些行更改服务器代码。

// Forcefully attaching socket to the port 8080                                                             
int resueaddr = setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));                         
int reuseport = setsockopt(server_fd, SOL_SOCKET, SO_REUSEPORT, &opt, sizeof(opt));                         

if (reuseaddr){                                                                                             
    perror("setsockopt addr");                                                                              
    exit(EXIT_FAILURE);                                                                                     
}                                                                                                           
if (reuseport){                                                                                             
    perror("setsockopt port");                                                                              
    exit(EXIT_FAILURE);                                                                                     
}