将具有指针的向量元素从一个派生类交换到另一派生类

我有一个国际象棋游戏，最初使用stl列表来存储棋子，为了获得更好的性能，我将其转换为向量。我知道载体不支持多态性，所以为了解决这个问题，我存储了一个<Unit *>的载体，而不是<Unit>。我所有的棋子对象（Pawn、Rook、Bishop等）都继承自Unit类。

然而，向量和堆损坏似乎仍然存在问题。我想我已经追踪到以下功能：

Unit *ChessGame::PromoteUnit(Unit *_oldUnit, UnitType _newType)
{
vector<Unit *> &army = (_oldUnit->m_gameColor == WHITE) ? m_whiteArmy : m_blackArmy;
Unit *newUnit = NULL;
for (unsigned int i = 0; i < army.size(); ++i)
{
    if (army[i]->m_subId == _oldUnit->m_subId)
    {
        if (_newType == QUEEN && _oldUnit->m_gameColor == WHITE)
        {
            newUnit = new Queen(*_oldUnit);
            newUnit->ActiveTexture_(m_textureMan->TextureId_(WhiteQueen));
        }
        else if (_newType == KNIGHT && _oldUnit->m_gameColor == WHITE)
        {
            newUnit = new Knight(*_oldUnit);
            newUnit->ActiveTexture_(m_textureMan->TextureId_(WhiteKnight));
        }
        else if (_newType == QUEEN && _oldUnit->m_gameColor == BLACK)
        {
            newUnit = new Queen(*_oldUnit);
            newUnit->ActiveTexture_(m_textureMan->TextureId_(BlackQueen));
        }
        else if (_newType == KNIGHT && _oldUnit->m_gameColor == BLACK)
        {
            newUnit = new Knight(*_oldUnit);
            newUnit->ActiveTexture_(m_textureMan->TextureId_(BlackKnight));
        }
        newUnit->m_wasPawn = true;
        delete army[i];
        army[i] = newUnit;
        break;
    }
}
m_selectedUnit = newUnit;
return newUnit;
}

既然一个指针无论指向什么都只有4个字节，那么在这种情况下，stl向量仍然会有问题是有原因的吗？我的Pawn对象比被提升为骑士或王后的对象大8个字节，这也许可以解释我一直以来出现的奇怪的内存错误。当我备份我的回合历史并点击降级功能来逆转升级时：

Unit *ChessGame::DemoteUnit(Unit *_oldUnit, UnitType _newType)
{
COUT("ChessGameManager::_DemoteUnit(Unit *, UnitType)");
vector<Unit *> &army = (_oldUnit->m_gameColor == WHITE) ? m_whiteArmy : m_blackArmy;
Unit *newUnit = NULL;
for (unsigned int i = 0; i < army.size(); ++i)
{
    if (army[i]->m_subId == _oldUnit->m_subId)
    {
        newUnit = new Pawn();
        newUnit->m_wasPawn = false;
        if (_oldUnit->m_gameColor == WHITE)
            newUnit->ActiveTexture_(m_textureMan->TextureId_(WhitePawn));
        newUnit->m_gameColor = _oldUnit->m_gameColor;
        newUnit->MobilityValid_(false);
        newUnit->Color_(RvColor::ClrWhite);
        newUnit->m_square = _oldUnit->m_square;
        newUnit->m_captured = false;
        newUnit->m_origin = _oldUnit->m_origin;
        newUnit->m_subId = _oldUnit->m_subId;
        newUnit->m_visible = true;
        //newUnit->m_square->m_unit = newUnit;
        delete army[i];
        army[i] = newUnit;
        break;
    }
}
return newUnit;
}

它真的崩溃了：

newUnit = new Pawn();

当它试图使用malloc来保留堆内存时，进入new Pawn（）会导致它在新操作符内崩溃。无论如何，我认为这仍然与我对向量stl的工作原理缺乏完全理解有关。我知道它与我的Pawn（）构造函数无关，因为它在游戏板初始化期间被调用了很多次。