端口号分配在UDP数据报和端口号在sockaddr_in

Question

在linux中：

我正在写一个代码来实现UDP套接字。

我想填充udp头字段，所以我必须分配源和目标端口号。

例如：

struct udphdr *udph  
//UDP header 
udph->source = htons (6666); 
udph->dest = htons (8622); 

此外，我必须准备结构sockaddr_in的，它包含一个端口号字段，例如：

//internet socket structure 
struct sockaddr_in sin; 
sin.sin_family = AF_INET; 
sin.sin_port = htons(80); 

是否有在SOCKADDR_IN端口号值之间的任何关系结构，这些在UDP头？

什么是分配这些值的正确方法？

这里是我的全码：

#include <stdio.h> 
#include <unistd.h> //sleep   
//socket headers 
#include <sys/types.h> 
#include <sys/socket.h> 
#include <errno.h> //when socket creation failed 
//#include <netinet/tcp.h> //Provides declarations for tcp header 
#include <netinet/udp.h> //Provides declarations for udp header 
#include <netinet/ip.h> //Provides declarations for ip header 
#include <stdlib.h> //for exit(); 
#include <string.h> //memset 
#include <netinet/in.h> 
#include <arpa/inet.h> 
int main() 
{ 
    //declarations 
    int sokt_fd; 
    //buffers 
    char datagram[80];// 80 bytes datagram 
    char *data;//buffer for payload 
    //code here 
    //Create a udp socket 
    if((sokt_fd=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) <0) 
    { 
     //socket creation failed, may be because of non-root privileges 
     perror("Failed to create socket"); 
     exit(1); 
    } 
    //zero out the packet buffer 
    memset (datagram, 0, 80); 
    //UDP header 
    struct udphdr *udph = (struct udphdr *) datagram;//assign startof udp 
    //Data part 
    data = datagram + sizeof(struct udphdr);//assigin location of data 
    strcpy(data , "ABC"); 
    //UDP header 
    udph->source = htons (6666); 
    udph->dest = htons (8622); 
    udph->len = htons(8 + strlen(data)); //UDP header size 
    //disable checksum 
    udph->check = 0; //leave checksum 0 now, filled later by pseudo header 
    //internet socket structure 
    //destination IP address, and port 
    //http://www.beej.us/guide/bgnet/output/html/singlepage/bgnet.html#sendtorecv 
    struct sockaddr_in sin; 
    sin.sin_family = AF_INET; 
    sin.sin_port = htons(80); 
    sin.sin_addr.s_addr = inet_addr ("10.0.0.2"); //destenation IP address, 

    //sending the datagram: 
    while(1) 
    { 
     if (sendto (sokt_fd,datagram,udph->len,0/*int flags*/,(struct sockaddr *) &sin, sizeof (sin))<0) 
     { 
      perror("sendto failed"); 
     } 
     else 
     { 
      printf ("Packet Send. Length : %d \n" , udph->len); 

     } 
     sleep(5); 
    } 
    return 0; 
} 

Answer 1

如果一个IPPROTO_UDP插座，你不招惹的UDP报头。

这是从一些片段发送UDP到127.0.0.1端口6666

struct in_addr in; 
struct sockaddr_in sdest; 

memset(&sdest, 0, sizeof(sdest)); 
sdest.sin_family = AF_INET; 
sdest.sin_port = htons(6666); 

inet_aton("127.0.0.1", &in); 
sdest.sin_addr.s_addr = in.s_addr; 
r = sendto(sock, data, size, 0, (struct sockaddr *) &sdest, (socklen_t) sizeof(sdest)); 

但你也应该看看bind为好。这允许你接收东西（总是有用的），但主要你应该看看W Richard Stevens等人在ISBN 0-13-141155-1中的Unix Network Programming的优秀例子。