在 C 中通过套接字发送结构

Question

I am trying to send struct over sockets. The connection works fine with arrays, but with a simple struct the server recieves only Recv - 1 - 1 If i change the ID or status to another number(while the client is running), it recieves nothing, but the client has sended. And if i change it back to ID=1 and status=1 it send it again and recieve it correctly.

Client-Side:

void func()
{
    printf("Send - %i - %i\n", mRELAIS.ID, mRELAIS.status);
    send(sockfd,&mRELAIS,sizeof(struct RELAIS),0);
}

Output: Send - 1 - 1 respectively Send - 1 - 0

Where i change it on the Client-Side:

if(temperature>(g_Value+g_PlusMinus) && relais[0]==0) 
{
    printf("%.1lf°C Relais wird 1 Soll %.1lf\n", temperature,(g_Value+g_PlusMinus)); 
    mRELAIS.ID=1;
    mRELAIS.status=1; 
    func();
}
else if(temperature<(g_Value-g_PlusMinus) && relais[0]==1) 
{
    printf("%.1lf°C Relais wird 0 Soll %.1lf\n", temperature,(g_Value-g_PlusMinus)); 
    mRELAIS.ID=1;
    mRELAIS.status=0; 
    func();
}

Server-Side:

for (;;)
{
    recv(connfd, &mRELAIS, sizeof(struct RELAIS),0);
    printf("Recv - %i - %i\n", mRELAIS.ID, mRELAIS.status);
    ....
}

Output: Send - 1 - 1 respectively

Does anyone have a suggestion to solve the problem? Thanks.

Answer 1

Not sure if this is your immediate problem but your receive code is wrong. Tco is a steaming protocol, not a message oriented one. You might receive a 50 byte send as 50 one byte receives. Or 2 25 bytes receives. You must lipp on recv till you have the entire send. There s in turn means that the receiver has to know the message size somehow