Why does the program run only once

Question

I have write server and client programs for experiment. I want achieve that effect: once server transfer "HELLO", the client w receive it and send back "HELLO FROM WIN" and wait for the next information. However, the server only get the first response and the client crushed(shutdown a few seconds later), Some codes are below.

client.c

int main(int argc, char * argv[]){
char receive[6] = "";
char *send = "HELLO FROM WIN";

startupWSA();
SOCKET sock = createTCPSocket();
    
while(1){
    recv(sock,receive,6,0);
    
    printf("%s\n",payload);
    printf("%s\n",receive);
    memset(receive,'\0',6);

    sendto(sock,send,16,0,(const struct sockaddr *)&addr,sizeof(addr));
    memset(send,'\0',16);

}
}

server.py

from socket import *
serverPort = 5555
serverSocket = socket(AF_INET,SOCK_STREAM)
serverSocket.bind(('',serverPort))
serverSocket.listen(1)
print('socket is ready')

connectionSocket,addr = serverSocket.accept()
while True:
    send = input('>')
    connectionSocket.send(send.encode())
    receive = connectionSocket.recv(1024).decode()
    print(receive)

Anyone can help me? Thanks.

Answer 1

char *send = "HELLO FROM WIN";

That's a pointer to a read-only string literal. In C you are allowed to have a non-const pointer to it (until C11 I believe), but you still cannot write to it. You try to do this here:

memset(send,'\0',16);

This is undefined behavior so crashing is a definite possibility (and a good one, too - much better than "working" until you deploy your code to production!)

To get around it you can change send to be an array with automatic storage:

char send[] = "HELLO FROM WIN";

And to make sure you don't write out of bounds:

sendto(sock,send,sizeof(send),0,(const struct sockaddr *)&addr,sizeof(addr));
memset(send, '\0', sizeof(send));