Programming Forums > Application Development > C++

King · Mar 3rd, 2006, 10:03 PM

In my program I have a server that will accepts a certain number of players for a card game. Each time a player is accepted it calls a function where the server gets the IP adress from the player that just connected and stores the IP in a vector. Then after all the players have connected i need the server to to loop threw the vector of IPs and send some info back to each player. As it loops threw the vector i wanted to use gethostbyname fucntion passing in the IP to connect to each player. The problem is that functions wants a char* to be passed in, and my vector is type string. I didn't know how to convert a string to that so i decided to make the vector of type char*. the problem with that is, when i call the functions to get the ip from the player, i would make a char to store the ip and then push it into the vector. But after that fucntion is done.. the vector isnt pointing to anything anymore and the data is lost. So how do i get this to work? a friend said i had to "new" the char in the function b4 pushing it into the vector.. but not sure how to do that. Any help would be great.. thanks guys. if you need me to post code i can.

The Dark · Mar 3rd, 2006, 11:33 PM

You could go back to using string and use the c_str() member function to convert the string to a const char *

King · Mar 4th, 2006, 12:34 AM

I tried that before and it didn't work, but i am thinking it was another bug because it works fine now. thanks

King · Mar 4th, 2006, 5:02 PM

OK I have another problem. Like I said above clients connect to the server passing their IPs in and then stored into a vector. Then after all the players have connect I want the server to loop threw all the IPs and send all the players a message that the game is starting. The problem is when the server tries sending somehting to the clients the server just stops running for some reason. Here is some code, I think i may be going about this a bit wrong:

(Toggle Plain Text)

int main(int argc, char *argv[])
{
  cout << "How many players are there going to be?" << endl;
  int numOfPlayers;
  cin >> numOfPlayers;
  cout << endl;
  
  acceptPlayers(numOfPlayers);
  sendMessage();
  
  return 0;
}

(Toggle Plain Text)

void acceptPlayers(int players)
{
  int numOfPlayers = players;
  // allocate and initialize permanent socket
  protoent *protTableEnt = getprotobyname("tcp");
  int socketDescriptor = socket(PF_INET, SOCK_STREAM, protTableEnt->p_proto);

  sockaddr_in servAddr = { 0 };
  servAddr.sin_family = AF_INET;
  servAddr.sin_addr.s_addr = INADDR_ANY;
  servAddr.sin_port = htons(1042);
  bind(socketDescriptor, (sockaddr *) & servAddr, sizeof(servAddr));

  // connect to clients
  listen(socketDescriptor, 26);

  int addrLen;
  sockaddr_in clientAddr = { 0 };
  int clientDescriptor;
  for(int i = 0; i != numOfPlayers; ++i)
  {
    addrLen = sizeof(clientAddr);
    clientDescriptor = accept(socketDescriptor, (sockaddr *) & clientAddr,
                              (socklen_t *) & addrLen);
     
    // create thread to get player's ip and store them into a vector
    pthread_t currentTID;
    if( pthread_create(&currentTID, NULL, (void *(*)(void *)) handleClient, (void *) &clientDescriptor) == 0)
      pthread_detach(currentTID);
    // else there was an error and thread not created;
    sleep(2);
  }
  shutdown(socketDescriptor, SHUT_RDWR);
}

(Toggle Plain Text)

void sendMessage()
{
  for(int i = 0; i !=  vecIP.size(); ++i)
  {
    hostent *hostTableEntry;
    hostTableEntry = gethostbyname(vecIP[i].c_str());

    // allocate and initialize socket
    protoent *protTableEnt = getprotobyname("tcp");
    int socketDescriptor = socket(PF_INET, SOCK_STREAM, protTableEnt->p_proto);
  
    // connect
    sockaddr_in sockAddr = { 0 };
    sockAddr.sin_family = AF_INET;
    memcpy(&sockAddr.sin_addr, hostTableEntry->h_addr, hostTableEntry->h_length);
    sockAddr.sin_port = htons(1042);
    connect(socketDescriptor, (sockaddr *) & sockAddr, sizeof(sockAddr));
  
    // send data
    char ip[25] = "Ready to start game!";
    send(socketDescriptor, ip, strlen(ip),0);
  
    shutdown(socketDescriptor,SHUT_RDWR);
  }
}

The Dark · Mar 5th, 2006, 6:15 AM

I'm not sure about why it shuts down, but this line looks wrong:

(Toggle Plain Text)

    if( pthread_create(&currentTID, NULL, (void *(*)(void *)) handleClient, (void *) &clientDescriptor) == 0)

You are passing the address of the same local variable to each new thread. This means that they will all (eventually) see the same value and that when the local variable goes out of scope, the value will be overwritten.

Kaja Fumei · Mar 5th, 2006, 1:22 PM

Quote:

Originally Posted by The Dark

I'm not sure about why it shuts down, but this line looks wrong:

(Toggle Plain Text)

    if( pthread_create(&currentTID, NULL, (void *(*)(void *)) handleClient, (void *) &clientDescriptor) == 0)

You are passing the address of the same local variable to each new thread. This means that they will all (eventually) see the same value and that when the local variable goes out of scope, the value will be overwritten.

I pointed this out in his last thread too: http://www.programmingforums.org/for...67&postcount=5

King · Mar 5th, 2006, 3:18 PM

OK i tried what Kaja Fumei said and it didnt work.. any other ideas?

The Dark · Mar 5th, 2006, 4:29 PM

Without all the code, I am just stabbing in the dark (hehe) here. You seem to by passing an IP address into gethostbyname, but gethostbyname takes a host name has its parameter, not an IP address. You should at the very least check the return value to function calls such as gethostbyname. If it is returning NULL, then your program will crash, as you dereference the pointer.

King · Mar 5th, 2006, 4:58 PM

no i checked it by hardcoding in the host and still didn't work.

nnxion · Mar 5th, 2006, 6:21 PM

Then like The Dark said show us more code.

Mar 3rd, 2006, 10:03 PM	#1
King Professional Programmer Join Date: Jan 2006 Location: Ontario, Canada Posts: 380 Rep Power: 3	Socket Problem! In my program I have a server that will accepts a certain number of players for a card game. Each time a player is accepted it calls a function where the server gets the IP adress from the player that just connected and stores the IP in a vector. Then after all the players have connected i need the server to to loop threw the vector of IPs and send some info back to each player. As it loops threw the vector i wanted to use gethostbyname fucntion passing in the IP to connect to each player. The problem is that functions wants a char* to be passed in, and my vector is type string. I didn't know how to convert a string to that so i decided to make the vector of type char*. the problem with that is, when i call the functions to get the ip from the player, i would make a char to store the ip and then push it into the vector. But after that fucntion is done.. the vector isnt pointing to anything anymore and the data is lost. So how do i get this to work? a friend said i had to "new" the char in the function b4 pushing it into the vector.. but not sure how to do that. Any help would be great.. thanks guys. if you need me to post code i can. __________________ I am Addicted to Linux!

Mar 4th, 2006, 12:34 AM	#3
King Professional Programmer Join Date: Jan 2006 Location: Ontario, Canada Posts: 380 Rep Power: 3	I tried that before and it didn't work, but i am thinking it was another bug because it works fine now. thanks __________________ I am Addicted to Linux!

Mar 4th, 2006, 5:02 PM	#4
King Professional Programmer Join Date: Jan 2006 Location: Ontario, Canada Posts: 380 Rep Power: 3	OK I have another problem. Like I said above clients connect to the server passing their IPs in and then stored into a vector. Then after all the players have connect I want the server to loop threw all the IPs and send all the players a message that the game is starting. The problem is when the server tries sending somehting to the clients the server just stops running for some reason. Here is some code, I think i may be going about this a bit wrong: (Toggle Plain Text) int main(int argc, char argv[]) { cout << "How many players are there going to be?" << endl; int numOfPlayers; cin >> numOfPlayers; cout << endl; acceptPlayers(numOfPlayers); sendMessage(); return 0; } int main(int argc, char argv[]) { cout << "How many players are there going to be?" << endl; int numOfPlayers; cin >> numOfPlayers; cout << endl; acceptPlayers(numOfPlayers); sendMessage(); return 0; } (Toggle Plain Text) void acceptPlayers(int players) { int numOfPlayers = players; // allocate and initialize permanent socket protoent protTableEnt = getprotobyname("tcp"); int socketDescriptor = socket(PF_INET, SOCK_STREAM, protTableEnt->p_proto); sockaddr_in servAddr = { 0 }; servAddr.sin_family = AF_INET; servAddr.sin_addr.s_addr = INADDR_ANY; servAddr.sin_port = htons(1042); bind(socketDescriptor, (sockaddr ) & servAddr, sizeof(servAddr)); // connect to clients listen(socketDescriptor, 26); int addrLen; sockaddr_in clientAddr = { 0 }; int clientDescriptor; for(int i = 0; i != numOfPlayers; ++i) { addrLen = sizeof(clientAddr); clientDescriptor = accept(socketDescriptor, (sockaddr ) & clientAddr, (socklen_t ) & addrLen); // create thread to get player's ip and store them into a vector pthread_t currentTID; if( pthread_create(&currentTID, NULL, (void ()(void )) handleClient, (void ) &clientDescriptor) == 0) pthread_detach(currentTID); // else there was an error and thread not created; sleep(2); } shutdown(socketDescriptor, SHUT_RDWR); } void acceptPlayers(int players) { int numOfPlayers = players; // allocate and initialize permanent socket protoent protTableEnt = getprotobyname("tcp"); int socketDescriptor = socket(PF_INET, SOCK_STREAM, protTableEnt->p_proto); sockaddr_in servAddr = { 0 }; servAddr.sin_family = AF_INET; servAddr.sin_addr.s_addr = INADDR_ANY; servAddr.sin_port = htons(1042); bind(socketDescriptor, (sockaddr ) & servAddr, sizeof(servAddr)); // connect to clients listen(socketDescriptor, 26); int addrLen; sockaddr_in clientAddr = { 0 }; int clientDescriptor; for(int i = 0; i != numOfPlayers; ++i) { addrLen = sizeof(clientAddr); clientDescriptor = accept(socketDescriptor, (sockaddr ) & clientAddr, (socklen_t ) & addrLen); // create thread to get player's ip and store them into a vector pthread_t currentTID; if( pthread_create(&currentTID, NULL, (void ()(void )) handleClient, (void ) &clientDescriptor) == 0) pthread_detach(currentTID); // else there was an error and thread not created; sleep(2); } shutdown(socketDescriptor, SHUT_RDWR); } (Toggle Plain Text) void sendMessage() { for(int i = 0; i != vecIP.size(); ++i) { hostent hostTableEntry; hostTableEntry = gethostbyname(vecIP[i].c_str()); // allocate and initialize socket protoent protTableEnt = getprotobyname("tcp"); int socketDescriptor = socket(PF_INET, SOCK_STREAM, protTableEnt->p_proto); // connect sockaddr_in sockAddr = { 0 }; sockAddr.sin_family = AF_INET; memcpy(&sockAddr.sin_addr, hostTableEntry->h_addr, hostTableEntry->h_length); sockAddr.sin_port = htons(1042); connect(socketDescriptor, (sockaddr ) & sockAddr, sizeof(sockAddr)); // send data char ip[25] = "Ready to start game!"; send(socketDescriptor, ip, strlen(ip),0); shutdown(socketDescriptor,SHUT_RDWR); } } void sendMessage() { for(int i = 0; i != vecIP.size(); ++i) { hostent hostTableEntry; hostTableEntry = gethostbyname(vecIP[i].c_str()); // allocate and initialize socket protoent protTableEnt = getprotobyname("tcp"); int socketDescriptor = socket(PF_INET, SOCK_STREAM, protTableEnt->p_proto); // connect sockaddr_in sockAddr = { 0 }; sockAddr.sin_family = AF_INET; memcpy(&sockAddr.sin_addr, hostTableEntry->h_addr, hostTableEntry->h_length); sockAddr.sin_port = htons(1042); connect(socketDescriptor, (sockaddr ) & sockAddr, sizeof(sockAddr)); // send data char ip[25] = "Ready to start game!"; send(socketDescriptor, ip, strlen(ip),0); shutdown(socketDescriptor,SHUT_RDWR); } } __________________ I am Addicted to Linux!

Mar 5th, 2006, 6:15 AM	#5
The Dark Expert Programmer Join Date: Jun 2005 Posts: 894 Rep Power: 4	I'm not sure about why it shuts down, but this line looks wrong: (Toggle Plain Text) if( pthread_create(&currentTID, NULL, (void ()(void )) handleClient, (void ) &clientDescriptor) == 0) if( pthread_create(&currentTID, NULL, (void ()(void )) handleClient, (void ) &clientDescriptor) == 0) You are passing the address of the same local variable to each new thread. This means that they will all (eventually) see the same value and that when the local variable goes out of scope, the value will be overwritten.

Mar 5th, 2006, 3:18 PM	#7
King Professional Programmer Join Date: Jan 2006 Location: Ontario, Canada Posts: 380 Rep Power: 3	OK i tried what Kaja Fumei said and it didnt work.. any other ideas? __________________ I am Addicted to Linux!

Mar 3rd, 2006, 11:33 PM	#2
The Dark Expert Programmer Join Date: Jun 2005 Posts: 894 Rep Power: 4	You could go back to using string and use the c_str() member function to convert the string to a const char *

Mar 5th, 2006, 4:29 PM	#8
The Dark Expert Programmer Join Date: Jun 2005 Posts: 894 Rep Power: 4	Without all the code, I am just stabbing in the dark (hehe) here. You seem to by passing an IP address into gethostbyname, but gethostbyname takes a host name has its parameter, not an IP address. You should at the very least check the return value to function calls such as gethostbyname. If it is returning NULL, then your program will crash, as you dereference the pointer.

Mar 5th, 2006, 4:58 PM	#9
King Professional Programmer Join Date: Jan 2006 Location: Ontario, Canada Posts: 380 Rep Power: 3	no i checked it by hardcoding in the host and still didn't work. __________________ I am Addicted to Linux!

Mar 5th, 2006, 6:21 PM	#10
nnxion Programming Guru Join Date: Jun 2005 Location: elemental plane Posts: 1,429 Rep Power: 5	Then like The Dark said show us more code. __________________ "Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." -- Socrates

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Programming Forums > Application Development > C++

Socket Problem!