程式語言 - GNU - C/C++ - UDP Server、Client

參考資訊：
https://www.geeksforgeeks.org/udp-client-server-using-connect-c-implementation/

server.c

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h>
#include <unistd.h>
#include <sys/types.h> 
#include <arpa/inet.h> 
#include <sys/socket.h> 
#include <netinet/in.h> 
  
int main(int argc, char **argv) 
{
    int r = 0;
    int fd = 0;
    int len = 0;
    char buf[255] = { 0 };
    struct sockaddr_in servaddr = { 0 };
    const char *hello = "hello from server !";
  
    if (argc != 3) {
        printf("Usage: %s IP Port\n", argv[0]);
        return 0;
    }
  
    fd = socket(AF_INET, SOCK_DGRAM, 0);
    servaddr.sin_addr.s_addr = inet_addr(argv[1]);
    servaddr.sin_port = htons(atoi(argv[2]));
    servaddr.sin_family = AF_INET;
  
    bind(fd, (struct sockaddr*)&servaddr, sizeof(servaddr));
  
    len = sizeof(struct sockaddr_in);
    r = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr*)&servaddr, &len);
    printf("%s (r=%d)\n", buf, r);
  
    sendto(fd, hello, strlen(hello), 0, (struct sockaddr*)&servaddr, sizeof(servaddr));
    close(fd);

    return 0;
}

client.c

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <arpa/inet.h> 
#include <sys/socket.h> 
#include <sys/types.h> 
#include <netinet/in.h> 
#include <unistd.h> 
    
int main(int argc, char **argv) 
{    
    int r = 0;
    int fd = -1;
    int len = 0;
    char buf[255] = { 0 };
    struct sockaddr_in servaddr = { 0 };
    const char *hello = "hello from client !";
  
    if (argc != 3) {
        printf("Usage: %s IP Port\n", argv[0]);
        return 0;
    }
  
    servaddr.sin_addr.s_addr = inet_addr(argv[1]);
    servaddr.sin_port = htons(atoi(argv[2]));
    servaddr.sin_family = AF_INET;
  
    fd = socket(AF_INET, SOCK_DGRAM, 0); 
    sendto(fd, hello, strlen(hello), 0, (struct sockaddr*)&servaddr, sizeof(servaddr));
  
    len = sizeof(struct sockaddr_in);
    r = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr*)&servaddr, (socklen_t *)&len);
    printf("%s (r=%d)\n", buf, r);
    close(fd);
 
    return 0;
}

編譯、執行

$ gcc server.c -o server
$ gcc client.c -o client

$ ./server 127.0.0.1 9999 &
$ ./client 127.0.0.1 9999
    hello from client ! (r=19)
    hello from server ! (r=19)