Programming Forums > Application Development > C++

King · Feb 28th, 2006, 4:30 PM

I am just starting socket programming in c++; I am just using regular sockets with TCP protocol. I have it so I can transfer text; is there a way I could transfer a whole object or vector? I am guessing I would have to send it as binary. If someone could send me some good links so I can do some research on how to that, that would be great. Thanks in advance.

Polyphemus_ · Feb 28th, 2006, 4:58 PM

A whole object is easy, as long as your object doesn't contain pointers:

(Toggle Plain Text)

objecttype nameofobject;

send(sock, (const char *) &nameofobject, sizeof(objecttype));

I don't know how to safe this code is. It should work with two programs compiled by the same compiler, I guess.

You can't send a vector this way. You'll have to put all the objects in an array and send it at once, or send the objects of the vector one by one.

King · Feb 28th, 2006, 11:07 PM

ok thanks.. i'll give it a try

King · Mar 1st, 2006, 1:54 AM

I have a couple more questions on sockets and threads:
On the server side I have a loop that accepts client connections untill it reaches a certain mumber of clients. After it accepts a client it threads a fucntiuon which will receive some data from the client. I threaded that part so it can still accept more clients while its dealing with the previouse one. Looks like this:

(Toggle Plain Text)

for(int i = 0; i != numOfClients; ++i)
  {
    addrLen = sizeof(clientAddr);
    clientDescriptor = accept(socketDescriptor, (sockaddr *) & clientAddr,
                              (socklen_t *) & addrLen);
    
    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;
  }
  shutdown(socketDescriptor, SHUT_RDWR);

The problem: Say I have it so i want 4 clients to be accepted, on the last itteration through the loop to deal with a client... it seems like the threaded fucntion to deal with the client isnt being accepted... any ideas why that would be? Right after the last line in the above code is the end of that function.. so maybe it is exiting the function before the thread is fisnished? Aslo the threaded functions edits some variables... should i use a mutex to make sure multple threads are not trying to edit data at the same time if 2 clients connect at the same time?

Thanks for any help guys!

Kaja Fumei · Mar 1st, 2006, 2:17 AM

One problem I see right away is that you pass in (void *) &clientDescriptor to the thread function. This is a problem because once a new connection is accepted, the clientDescriptor variable gets changed for all the currently running threads. One way to fix this is to allocate a new int for each new client descriptor:

(Toggle Plain Text)

int *clientDescriptor = new int;
*clientDescriptor = accept(socketDescriptor, (sockaddr *) & clientAddr,
                              (socklen_t *) & addrLen);

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

If threads edit only local variables that no other threads can edit, you don't need a mutex. But if a thread is changing data that other running threads could also change, you're going to need some sort of lock (typically a mutex).

Feb 28th, 2006, 4:30 PM	#1
King Professional Programmer Join Date: Jan 2006 Location: Ontario, Canada Posts: 380 Rep Power: 3	Socket Question I am just starting socket programming in c++; I am just using regular sockets with TCP protocol. I have it so I can transfer text; is there a way I could transfer a whole object or vector? I am guessing I would have to send it as binary. If someone could send me some good links so I can do some research on how to that, that would be great. Thanks in advance. __________________ I am Addicted to Linux!

Feb 28th, 2006, 4:58 PM	#2
Polyphemus_ Expert Programmer Join Date: Aug 2005 Location: Rotterdam, the Netherlands Posts: 942 Rep Power: 4	A whole object is easy, as long as your object doesn't contain pointers: (Toggle Plain Text) objecttype nameofobject; send(sock, (const char ) &nameofobject, sizeof(objecttype)); objecttype nameofobject; send(sock, (const char ) &nameofobject, sizeof(objecttype)); I don't know how to safe this code is. It should work with two programs compiled by the same compiler, I guess. You can't send a vector this way. You'll have to put all the objects in an array and send it at once, or send the objects of the vector one by one.

Feb 28th, 2006, 11:07 PM	#3
King Professional Programmer Join Date: Jan 2006 Location: Ontario, Canada Posts: 380 Rep Power: 3	ok thanks.. i'll give it a try __________________ I am Addicted to Linux!

Mar 1st, 2006, 1:54 AM	#4
King Professional Programmer Join Date: Jan 2006 Location: Ontario, Canada Posts: 380 Rep Power: 3	I have a couple more questions on sockets and threads: On the server side I have a loop that accepts client connections untill it reaches a certain mumber of clients. After it accepts a client it threads a fucntiuon which will receive some data from the client. I threaded that part so it can still accept more clients while its dealing with the previouse one. Looks like this: (Toggle Plain Text) for(int i = 0; i != numOfClients; ++i) { addrLen = sizeof(clientAddr); clientDescriptor = accept(socketDescriptor, (sockaddr ) & clientAddr, (socklen_t ) & addrLen); 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; } shutdown(socketDescriptor, SHUT_RDWR); for(int i = 0; i != numOfClients; ++i) { addrLen = sizeof(clientAddr); clientDescriptor = accept(socketDescriptor, (sockaddr ) & clientAddr, (socklen_t ) & addrLen); 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; } shutdown(socketDescriptor, SHUT_RDWR); The problem: Say I have it so i want 4 clients to be accepted, on the last itteration through the loop to deal with a client... it seems like the threaded fucntion to deal with the client isnt being accepted... any ideas why that would be? Right after the last line in the above code is the end of that function.. so maybe it is exiting the function before the thread is fisnished? Aslo the threaded functions edits some variables... should i use a mutex to make sure multple threads are not trying to edit data at the same time if 2 clients connect at the same time? Thanks for any help guys! __________________ I am Addicted to Linux!

Mar 1st, 2006, 2:17 AM	#5
Kaja Fumei Hobbyist Programmer Join Date: Oct 2005 Posts: 134 Rep Power: 4	One problem I see right away is that you pass in (void ) &clientDescriptor to the thread function. This is a problem because once a new connection is accepted, the clientDescriptor variable gets changed for all the currently running threads. One way to fix this is to allocate a new int for each new client descriptor: (Toggle Plain Text) int clientDescriptor = new int; clientDescriptor = accept(socketDescriptor, (sockaddr ) & clientAddr, (socklen_t ) & addrLen); pthread_t currentTID; if( pthread_create(&currentTID, NULL, (void ()(void )) handleClient, clientDescriptor) == 0) pthread_detach(currentTID); int clientDescriptor = new int; clientDescriptor = accept(socketDescriptor, (sockaddr ) & clientAddr, (socklen_t ) & addrLen); pthread_t currentTID; if( pthread_create(&currentTID, NULL, (void ()(void *)) handleClient, clientDescriptor) == 0) pthread_detach(currentTID); If threads edit only local variables that no other threads can edit, you don't need a mutex. But if a thread is changing data that other running threads could also change, you're going to need some sort of lock (typically a mutex).

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Programming Forums > Application Development > C++

Socket Question