代码需要太多内存

Question

I'm porting some code to another structure:

class EnvironObject
{
   protected:
      vector<float> mX, mY, mXSpeed, mYSpeed;
      int mMaxObjects;

   public:
      virtual void init(int maxObjects);
      virtual void setLimit(int limit);
      virtual int getLimit();
      virtual void update(float arg) = 0;
};

void EnvironObject::setLimit(int limit)
{
   mMaxObjects = limit;

   mX.resize(limit, 0); mY.resize(limit, 0);
   mXSpeed.resize(limit, 0); mY.resize(limit, 0);
}

int EnvironObject::getLimit()
{
   return mMaxObjects;
}

void EnvironObject::init(int maxObjects)
{
    mX = mY = mXSpeed = mYSpeed = std::vector<float>(mMaxObjects);

    fill(mX.begin(), mX.end(), 0);
    fill(mY.begin(), mY.end(), 0);
    fill(mXSpeed.begin(), mXSpeed.end(), 0);
    fill(mYSpeed.begin(), mYSpeed.end(), 0);

    /*mX.reserve(mMaxObjects * 1.5); mY.reserve(mMaxObjects * 1.5);
    mXSpeed.reserve(mMaxObjects * 1.5); mYSpeed.reserve(mMaxObjects * 1.5);*/

    mMaxObjects = maxObjects;
}

This is some basic class, now it's usage:

class Rain : public EnvironObject
{
    public:
        Rain(int maxDrops = 150);
        void update(float windPower);
};

Rain::Rain(int maxDrops)
{
    srand(time(NULL));

    IEnvironObject::init(maxDrops);
}

void Rain::update(float windPower)
{
    for (int i=0; i < mMaxObjects; i++)
    {
       mX[i] += mXSpeed[i];
       mY[i] += mYSpeed[i];

       mXSpeed[i] += windPower;
       mYSpeed[i] += G;

   // Drawing
    }
}

The objects Rain creates with default constructor (so, each array is 150 elements size) and then I'm calling setLimit(50) . The problem is that code fails almost each running with exception:

terminate called after throwing an instance of 'std::bad_alloc'

And sometimes it segfaults at line:

mY[i] += mYSpeed[i];

I can't image what could it be, because the code is old and it worked. The new one is only base class.

And when I'm looking at RAM usage when starting app, I see almost +600 mb!

Answer 1

Look again at that function of yours:

void EnvironObject::init(int maxObjects)
{
    mX = mY = mXSpeed = mYSpeed = std::vector<float>(mMaxObjects);
    //                                               ^
    // ...

    mMaxObjects = maxObjects;
}

You're using a not yet initialized variable.

A big problem with your class is that you are doing what's called two-phase construction. Your class EnvironObject has a compiler-supplied default constructor that creates an object with random values for all POD types ( mMaxObjects ). Users then need to call the init() method to really initialize the object. But that's what constructors are there for!

void EnvironObject::EnvironObject(int maxObjects)
  : mMaxObjects(maxObjects)
  , mX(maxObjects), mY(maxObjects), mXSpeed(maxObjects), mYSpeed(maxObjects)
{
    /* these aren't necessary, std::vector automatically does this
    fill(mX.begin(), mX.end(), 0);
    fill(mY.begin(), mY.end(), 0);
    fill(mXSpeed.begin(), mXSpeed.end(), 0);
    fill(mYSpeed.begin(), mYSpeed.end(), 0);
    */
}

Derived classes can then use this constructor:

Rain::Rain(int maxDrops)
 : EnvironObject(maxDrops)
{
    srand(time(NULL));
}

---

Regarding this crash in the subscription mY[i] += mYSpeed[i] :

This might happen when you are calling this function through a pointer that's pointing to nowhere.

Answer 2

You're using mMaxObjects in init() before initializing it. So it has a random value.

void EnvironObject::init(int maxObjects) 
{ 
   mX = mY = mXSpeed = mYSpeed = std::vector<float>(mMaxObjects);  // you mean maxObjects here

Answer 3

I think you want to replace

void EnvironObject::init(int maxObjects)
{
    mX = mY = mXSpeed = mYSpeed = std::vector<float>(mMaxObjects);

with

void EnvironObject::init(int maxObjects)
{
    mX = mY = mXSpeed = mYSpeed = std::vector<float>(maxObjects);

Notice the replacement of mMaxObject to maxObjects in the vector creation.

Answer 4

一条评论虽然可能不会解决您的内存错误，但由于字段mX，mY，mXSpeed和mYSpeed似乎相关并且向量大小都相同，因此您应该考虑将它们合并为一个具有四个成员的结构，并具有包含多个这些结构实例的单个向量。