如何检查是否有足够的堆内存可用? [英] How can I check if there is enough heap memory available?

问题描述

我有一个作业，要求我创建一个分配和取消分配内存的"Heap"类.我相信我的代码可以正常工作，并且该解决方案可以正确构建和运行，但是我想确保没有任何内存泄漏.我还需要添加一些代码来检查分配给堆的期望数量是否可用……如果有人要分配非常大的数量.如何检查在堆上分配的内存是否可用，如果没有足够的内存，则如何检查为NULL.到目前为止，这是我的代码:

I have an assignment that requires me to create a "Heap" class that allocates and deallocates memory. I believe that my code works and the solution builds and runs properly but I want to make sure that I am not getting any memory leaks. I also need to add some code that checks if the desired amount to be allocated to the heap is even available...if someone were to allocate a very large amount. How is it possible to check if the memory allocated on the heap is available or NULL if there is not enough memory. Here is my code so far:

#include <iostream>
using namespace std;

class Heap{
public:

double* allocateMemory(int memorySize)
{
    return new double[memorySize];
};
void deallocateMemory(double* dMemorySize)
{
    delete[] dMemorySize;
};

};

int main()
{
Heap heap;
cout << "Enter the number of double elements that you want to allocate: " << endl;
int hMemory;
const int doubleByteSize = 8;
cin >> hMemory;

double *chunkNew = heap.allocateMemory(hMemory);

cout << "The amount of space you took up on the heap is: " <<
         hMemory*doubleByteSize << " bytes" << 
     starting at address: " << "\n" << &hMemory << endl; 

heap.deallocateMemory(chunkNew);

system("pause");
return 0;
}

推荐答案

没有必要事先检查，只需尝试分配内存，如果不能，则捕获异常.在这种情况下，它的类型为bad_alloc.

It's not necessary to check beforehand, just try to allocate memory and if you can't, then catch the exception. In this case it is of type bad_alloc.

#include <iostream>
#include <new>      // included for std::bad_alloc

/**
 * Allocates memory of size memorySize and returns pointer to it, or NULL if not enough memory.
 */
double* allocateMemory(int memorySize)
{
  double* tReturn = NULL;

  try
  {
     tReturn = new double[memorySize];
  }
  catch (bad_alloc& badAlloc)
  {
    cerr << "bad_alloc caught, not enough memory: " << badAlloc.what() << endl;
  }

  return tReturn;
};

重要提示

请确保防止双重释放内存.一种方法是通过引用将指针传递到deallocateMemory，允许该函数将指针值更改为NULL，从而防止delete两次将指针赋值.

Important note

Be sure to guard against double-freeing memory. One way to do that would be to pass your pointer to deallocateMemory by reference, allowing the function to change the pointer value to NULL, thereby preventing the possibility of delete-ing the pointer twice.

void deallocateMemory(double* &dMemorySize)
{
   delete[] dMemorySize;
   dMemorySize = NULL; // Make sure memory doesn't point to anything.
};

这可以防止出现以下问题:

This prevents problems like the following:

double *chunkNew = heap.allocateMemory(hMemory);
heap.deallocateMemory(chunkNew);
heap.deallocateMemory(chunkNew); // chunkNew has been freed twice!

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