C语言实现udp

#include <stdio.h>
#include <strings.h>
#include "arpa/inet.h"

typedef union std {
    unsigned short a;
    unsigned char b[2];

} STD;

void udp_server() {
    int sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sock_fd < 0) {
        perror("");
    }
    //绑定
    //
    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(9090);
    //绑定自己本机的ip
//    inet_pton(AF_INET,"192.168.127.129",&addr.sin_addr.s_addr);
    addr.sin_addr.s_addr = INADDR_ANY; //通配地址
    int ret=bind(sock_fd,(struct sockaddr*)&addr,sizeof(addr));
    if(ret<0){
        perror("");
    }
    struct sockaddr_in cli_addr;
    socklen_t  len = sizeof(cli_addr);
    while (1){
        char buf[128]="";
        int n = recvfrom(sock_fd,buf, sizeof(buf),0,(struct sockaddr*)&cli_addr, &len);
        printf("%s\n",buf);
        sendto(sock_fd,buf,n,0,(struct sockaddr*)&cli_addr, sizeof(cli_addr));
    }
    close(sock_fd)

}

void udp_client() {
    //ipv4的套接字结构体
    struct sockaddr_in server_addr;
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(9000);//转大端，这是目标机器的port
    inet_pton(AF_INET, "192.168.127.1", &server_addr.sin_addr.s_addr);
    // 创建套接字
    int sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sock_fd < 0) {
        perror("");
    }
    while (1) {
        char buf[128] = "";
        fgets(buf, sizeof(buf), stdin);
        buf[strlen(buf) - 1] = 0;
        sendto(sock_fd, buf, strlen(buf), 0, (struct sockaddr *) &server_addr, sizeof(server_addr));
        char read_buf[128] = "";
        recvfrom(sock_fd, read_buf, sizeof(read_buf), 0, NULL, NULL);
        printf("%s\n", read_buf);
    }
}

void func2() {
    //字符串ip地址转为整型数据
    char buf_ip[] = "192.168.1.2";
    int num = 0;
    inet_pton(AF_INET, buf_ip, &num);
    unsigned char *p = (char *) &num; //不定义为无符号容易出现负数。
    printf("%d %d %d %d\n", *p, *(p + 1), *(p + 2), *(p + 3));

    //将网络32位大端数据转为点分十进制

    char ip[INET_ADDRSTRLEN] = "";  //INET_ADDRSTRLEN=16 255.255.255.2555\0,最大就是16位就够了。其中'\0'占一位
    inet_ntop(AF_INET, &num, ip, INET_ADDRSTRLEN);
    printf("ip=%s\n", ip);

}

void func1() {
    int num = 0x01020304;//小端
    short a = 0x0102;
    int num2 = htonl(num);//小端转为大端数据。4030201
    short a2 = htons(a);
    printf("%x\n", a2);
    printf("%x\n", num2);
    printf("%x\n", ntohl(num2)); //大端再转为小端。
    printf("%x\n", ntohs(a2)); //大端再转为小端。

}


int main() {
    STD tmp;
    tmp.a = 0x0102;
    if (tmp.b[0] == 0x01) {
        printf("大端");
    } else {
        printf("小端");
    }
    printf("Hello, World!\n");
    func1();
    func2();
    return 0;
}