Question

我正在使用UDP协议实现双向通信，最初我从客户端向服务器发送消息HELO，该服务器成功显示在服务器端但是当我从服务器向客户端发送消息以回复HELO时它给了我错误：地址系列协议不支持。

这是我的服务器代码：

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



using namespace std;
int main(void)
    {
    char write[100];
    int MAXBUFLEN=100;
    char* buf;
    char msg[100];
    char swp;
    int l,x,y;

    int conn_sock,n,err;
    struct sockaddr_in server_addr,client_addr;

    conn_sock=socket(AF_INET,SOCK_DGRAM,0);
    if(conn_sock == -1)
    {
    perror("\n\nError in making socket and error is");

    cout<<"Error No:\t\n"<<errno;
    exit(0);
    }

    server_addr.sin_family= AF_INET;
    server_addr.sin_port = 1234;
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

    err=bind(conn_sock,(struct sockaddr *)&server_addr,sizeof(server_addr)); // binding...

    if(err == -1)
    {

    perror("\n\nError in binding and error is:");
    cout<<"Error No:\t\n"<<errno;
    exit(0);
    }
    int s=sizeof(client_addr);

    n=recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&client_addr,(socklen_t*)s); // reciving HELO from client..


    cout<<msg<<endl;

    cout<<"The messgae hasbeen recieved from client now enter a reply for HELO msg:"<<endl;
    cin>> write;

    // sending reply to client

    int m=sendto(conn_sock,write,strlen(write),0,(sockaddr *)&client_addr,s); // sending reply to client on reply of helo...
    if (m== -1){
     perror("talker: sendto");
    }
    // now recieve mail fromm...

    recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&client_addr,(socklen_t*)s);

// sending rcpto client
    sendto(conn_sock,write,strlen(write),0,(sockaddr *)&client_addr,s);
    recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&client_addr,(socklen_t*)s);
    cout<<"Recpt to: Nu.edu.pk"<<endl;  
    exit(0);

}

这是我的客户代码：

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

#define SERVERPORT "4950"    // the port users will be connecting to
#define MAXBUFLEN 100
using namespace std;

int main(int argc, char*argv[])

{

    // declarations
    char msg3[]="DATA";
    int sockfd;
        struct addrinfo hints, *servinfo, *p;
        int rv;
        int numbytes;
        char buf[MAXBUFLEN];
        socklen_t addr_len;
        struct sockaddr_storage their_addr;
    char* bigarray;
    char msg[]="HELO";
    char msg2[]="Mail from: Mahnoorfatima@gmail.com";   
    int i=0;

    char * adress;
    char * subject;
    char * name;
    const char *delim="@";
    // getting commandline args into arrays.
    adress=argv[i+1];
    char* host=strtok(adress,delim );
    subject=argv[i+2];
    name=argv[i+3];


    // putting all in one array

    bigarray=adress;
    bigarray=subject;
    bigarray=name;




    if(argc>9){
    cout << "Just provide three arguments in commandline,please. " << endl;
        }

    // gets the name of the host:

    int a=gethostname(bigarray, 100);

    cout<<"The host of the client is:"<<a<<endl;


    int conn_sock,n,m,err;
    struct sockaddr_in server_addr;
    conn_sock=socket(AF_INET,SOCK_DGRAM,0);

    if(conn_sock ==-1)
    {
    perror("\n\nError in making socket and error is");

    cout<<"Error No:\t\n"<<errno;
    exit(0);
    }


    server_addr.sin_family= AF_INET;
    server_addr.sin_port = 1234;
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");


    int pp=sizeof(server_addr);
    n=sendto(conn_sock,msg,strlen(msg),0,(sockaddr *)&server_addr,pp);//sending HELO to server...

    n=recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&server_addr,(socklen_t*)pp);
    cout<<"Mail from: mahnoorfatima22@gmail.com"<<endl;
    n=sendto(conn_sock,msg2,strlen(msg2),0,(sockaddr *)&server_addr,pp);


        // sending file to server

    // reieving from server rcpto command

    recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&server_addr,(socklen_t*)pp);   

    // sending data command to the server....

    n=sendto(conn_sock,msg3,strlen(msg3),0,(sockaddr *)&server_addr,pp);
        //Sending the filename to server...
        if ((n = sendto(sockfd,name,strlen(name), 0,p->ai_addr, p->ai_addrlen)) == -1) {
        //     perror("Error is sending");
                exit(1);
                                                }              
        //     Get the size of the file server sy 

    addr_len = sizeof their_addr;
        if ((n = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,(struct sockaddr *)&their_addr, &addr_len)) == -1) {
        //     perror("Error in recieving file");
         exit(1);
                                                        }


        cout<<"client: recieved file size: %s\nNumbytes:%d\n"<<buf<<numbytes;





    exit(0);

    }

Answer 1

问题很可能是recvfrom函数需要指针到套接字地址结构大小，而你提供长度值。这意味着编译器认为您设置的大小（sizeof(client_addr)）被解释为指针，无论结构大小如何，它都不是有效指针或指向远程有效的东西。

这意味着recvfrom可能无法完全填写对等地址结构（client_addr），从而导致sendto失败。

尝试例如相反：

n=recvfrom(conn_sock,msg,sizeof(msg),0,
          (struct sockaddr *)&client_addr,&s);
//                                        ^
//                                        |
//            Note address-of operator here

为什么我收到协议不支持的地址族错误？

1 个答案: