Incorrect data when passing pointer a list of pointers to a function. (C++)

Posted by Phil Elm on Stack Overflow See other posts from Stack Overflow or by Phil Elm
Published on 2011-11-28T01:30:43Z Indexed on 2011/11/28 1:49 UTC
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I'm writing code for combining data received over multiple sources. When the objects received (I'll call them MyPacket for now), they are stored in a standard list.

However, whenever I reference the payload size of a partial MyPacket, the value shows up as 1 instead of the intended size.

Here's the function code:

MyPacket* CombinePackets(std::list<MyPacket*>* packets, uint8* current_packet){
       uint32 total_payload_size = 0;
       if(packets->size() <= 0) return NULL; //For now.
       std::list<MyPacket*>::iterator it = packets->begin();
       //Some minor code here, not relevant to the problem.
       for(uint8 index = 0; index < packets->size(); index++){
             //(*it)->GetPayloadSize() returns 1 when it should show 1024. I've tried directly accessing the variable and more, but I just can't get it to work.
             total_payload_size += (*it)->GetPayloadSize(); 
             cout << "Adding to total payload size value: " << (*it)->GetPayloadSize() << endl;
             std::advance(it,1);
       }

       MyPacket* packet = new MyPacket();
       //Byte is just a typedef'd unsigned char.
       packet->payload = (byte) calloc(total_payload_size, sizeof(byte));
       packet->payload_size = total_payload_size;

       it = packets->begin(); //Go back to the beginning again.
       uint32 big_payload_index = 0;
       for(uint8 index = 0; index < packets->size(); index++){
              if(current_packet != NULL) *current_packet = index;
              for(uint32 payload_index = 0; payload_index < (*it)->GetPayloadSize(); payload_index++){
                   packet->payload[big_payload_index] = (*it)->payload[payload_index];
                   big_payload_index++;
              }
              std::advance(it,1);

       }

       return packet;

}

//Calling code
std::list<MyPacket*> received = std::list<MyPacket*>();
//The code that fills it is here.
std::list<MyPacket*>::iterator it = received.begin();
cout << (*it)->GetPayloadSize() << endl; // Outputs 1024 correctly!
MyPacket* final = CombinePackets(&received,NULL);
cout << final->GetPayloadSize() << endl; //Outputs 181, which happens to be the number of elements in the received list.

So, as you can see above, when I reference (*it)->GetPayloadSize(), it returns 1 instead of the intended 1024.

Can anyone see the problem and if so, do you have an idea on how to fix this? I've spent 4 hours searching and trying new solutions, but they all keep returning 1...

EDIT:

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