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c++ - 指针值在分配后不久重置为空

转载 作者:太空宇宙 更新时间:2023-11-03 10:32:06 26 4
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我有一个指针设置为 0 ,然后在同一个函数中,在一些循环/条件中我尝试重新分配它..(请阅读评论)

for(Entity* tile : _originalFloorTiles)
{
for(Turns turn : pointsUpLeftDownRight)
{
if(tile->GetCollisionRect().ContainsPoint(turn.first.x, turn.first.y)){
turn.second = tile; //everything looks fine here, turn.second is still null and tile is a valid pointer
assert(turn.second); //turn.second is definitely assigned the value of tile here.
}
HAPI->DebugText("check pointsUpLeftDownRight now");//!Here's where it gets weird,
// If i hover over turn and inspect it in visual studio now, turn.second is still completely valid
// (with the assigned value of tile).
// But hovering over pointsUpLeftDownRight shows its contents for each turn..
// and inside there the current turn is a NULL pointer for turn.second!
}
}

所以前一刻我已经分配我的指针没有问题,下一刻指针似乎根本没有改变。

为了澄清,Turnsstd::pair<Vect, Entity*> 的惰性 typedef ,如果这让我的代码更难阅读,我深表歉意,它是一些快速拼凑的敌人 ai。我将在下面发布完整的功能。

我真的被难住了,不确定我是不是个白痴或发生了什么奇怪的事情,真的很感谢任何人花时间看看。

//寻找幽灵可以进行的回合。

void IceGhostNPC::RespondToTimePassed()
{
//Entity* t = _originalFloorTiles[0];

//test if enough time has passed since ghost last decided to look for turns
if(_lastTimeTurned < timeGetTime() - _timeBeforeSearchingForTurns)
{
//store points surrounding ghost in a way that we can associate them with a valid floor tile to move onto
std::vector<Turns> pointsUpLeftDownRight;
pointsUpLeftDownRight.push_back(
Turns(Vect(GetCenterXPos(), GetCenterYPos() - floorTileHeight), 0)); //point above
pointsUpLeftDownRight.push_back(
Turns(Vect(GetCenterXPos() - floorTileWidth, GetCenterYPos()), 0)); //point left
pointsUpLeftDownRight.push_back(
Turns(Vect(GetCenterXPos(), GetCenterYPos() + floorTileHeight), 0)); //point down
pointsUpLeftDownRight.push_back(
Turns(Vect(GetCenterXPos() + floorTileWidth, GetCenterYPos()), 0)); //point right

//look through original floor tiles,
for(Entity* tile : _originalFloorTiles)
{
//see if its possible to take a turn
for(Turns turn : pointsUpLeftDownRight)
{
if(tile->GetCollisionRect().ContainsPoint(turn.first.x, turn.first.y)){
turn.second = tile;
assert(turn.second);
}
HAPI->DebugText("check pointsUpLeftDownRight now");
}
}

//Now to make the behaviour more interesting we have the ghost randomly take one of the turns,
// ( we use associated tile to check the turn is possible, and we can also change that tile to an icy patch )
bool turnTaken = false;
do{
int turnChoice = rand() % 4;
if(pointsUpLeftDownRight[turnChoice].second == 0)
continue; //go back to top of loop if that turn had a null tile
else
{
switch(turnChoice){
case 0: //turn upwards
_moveable->SetYDirection(Controller::UP);
_moveable->SetXDirection(Controller::NONE);
break;
case 1: //turn leftwards
_moveable->SetYDirection(Controller::NONE);
_moveable->SetXDirection(Controller::LEFT);
break;
case 2: //turn downwards
_moveable->SetYDirection(Controller::DOWN);
_moveable->SetXDirection(Controller::NONE);
break;
case 3: //turn right
_moveable->SetYDirection(Controller::NONE);
_moveable->SetXDirection(Controller::RIGHT);
break;
}
turnTaken = true;
_lastTimeTurned = timeGetTime();
//ice tile up baby
}

}while(turnTaken = false);
}

FinishResponding(timeGetTime());
}

最佳答案

检查这一行:

for(Turns turn : pointsUpLeftDownRight)

您正在遍历 pointsUpLeftDownRight 中元素的拷贝。当拷贝被销毁时(在 for 主体的末尾),您分配给该拷贝的任何值都将丢失。您的任务临时更改。

试试这个:

for(Turns& turn : pointsUpLeftDownRight)

关于c++ - 指针值在分配后不久重置为空,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13958726/

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