__sync_bool_compare_and_swap not working

// created a copy of CNode and added the new value
    CNode *copyCNode = new CNode;
    //memcpy(c, iNode->mainNode->cNode, sizeof(*(iNode->mainNode->cNode)) );
    memcpy(copyCNode, iNode->mainNode->cNode, sizeof(CNode) );

    CNode *updated_cnode = inserted(copyCNode, b, index);  
    std::cout << "temporay CNode created : " << updated_cnode->branch[index]->sNode->value << std::endl;

        if(memcmp(copyCNode, iNode->mainNode->cNode, sizeof(CNode)) == 0){
            std::cout << "mainNode is not changed " << std::endl ;
        }else{
            std::cout << "mainNode is changed" << std::endl;
        }

    bool cas_ret = __sync_bool_compare_and_swap(&iNode->mainNode->cNode, copyCNode, updated_cnode);
    std::cout << "return cas_ret : " << cas_ret << std::endl;
    if(cas_ret){
        std::cout << "New added value " << iNode->mainNode->cNode->branch[index]->sNode->value << std::endl;
        return 0; // successfully attached the node
    }
    else{
        return 1;
    }

The above code is part of my code base. There is no compilation error and the code is running fine. But __sync_bool_compare_and_swap function always return false in my code. Even before the CAS function call I did the memory comparison (memcpy) and its showing that both the arguments are equal, in that case CAS should swap the value with third argument, but it is not. Please suggest. Thanks