Virtual Heap Class


You are to implement a C++ class that functions as a memory heap.


The virtual class v_heap.h has been provided, and must be implemented by your child class. The child class will be named MemHeap and it will be written in the files mem_heap.h and mem_heap.cpp. You must also write a program in main.cpp that thoroughly tests your heap implementation. Use print outs and assert statements accordingly.


In case you are wondering what the point of this is …..........................


This technique has been used by programmers in the past to avoid the overhead of making a call to the operating system to allocate and de-allocate memory. By allocating all the memory upfront, there is only 1 system call to allocate memory, and 1 system call to de-allocate memory, the rest is just pointer manipulation.


Implementing this technique also gives you a small insight into how memory management is handled “under the hood”.


The v_heap.h virtual class has been provided, its content follows.


#ifndef VHEAP_H

#define VHEAP_H


#include <cstdlib>


#define HEAP_SIZE 2048


class VHeap {

protected:

char * vheap;



public:

VHeap()

{

vheap = new char[HEAP_SIZE];

}



virtual void* vnew(size_t size) {}



virtual void* vcnew(size_t size) {}



virtual void vdelete(void* mem) {}



virtual size_t vsizeof(void* mem) {}



virtual void printHeapState() {}



virtual ~VHeap()

{

delete [] vheap;

}

};


#endif // VHEAP_H


Parts of v_heap.h explained


char * vheap;

Pointer to the memory allocated for the heap. You should not use this pointer directly, but rather assign another pointer to the address vheap holds, that way you wont inadvertently lose track of the start address of the heap.

Heap()

{

vheap = new char[HEAP_SIZE];

}

A constructor where the total amount of memory required for the heap is allocated.




virtual void* vnew(size_t size) {}

A user (main.cpp) can use this function to request memory (to be allocated within the heap).

The vnew function will allocate memory to the length of the parameter size, and it will return the address of the start of the allocated memory. The return type is void so as to handle any datatype. As you need to supply the size in bytes, you may find the function sizeof useful.


To use vnew to allocate a int, in main.cpp you would write

int *myNewInt = (int*)heapObj.vnew(sizeof(int));


To use vnew to allocate an array of long's that holds 5 items, in main.cpp you would write

long * myLongArr = (long*)heapObj.vnew(sizeof(long) * 5);




virtual void* vcnew(size_t size) {}

Functions the same as vnew but it also sets the allocated data to all 0's, where as vnew will leave whatever 'Junk' is in the allocated space.




virtual void vdelete(void* mem) {}

A release method where the user can return previously allocated memory back to the heap. When memory is released it should ensure that adjacent, available memory segments are consolidated into a single available segment.






virtual size_t vsizeof(void* mem) {}

Returns the amount of memory, in bytes, allocated at mem.






virtual void printHeapState() {}

A method which describes the in-use / available segments of the heap.

The following is an example of the output from printHeapState() where 'I' indicates areas being used for heap information, 'D' is allocated memory used to hold data and 'F' is for free/unused bytes.

IIIIIIIIIIIIIIIIIIIIIIIIDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDIIIIIIIIIIIIIIII

IIIIIIIIDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD

DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDIIIIIIIIIIIIIIIIIIIIIIIIFFFFFFFF

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF


virtual ~VHeap()

{

delete [] vheap;

}



A destructor to release the memory associated with the heap back to the system.


You will also be marked on correct style, ie consistent indenting, appropriate variable naming etc.


Every Function Must have commenting in the style of


/**

* This function is only an example

* and does not actually do anything

*

* It returns nothing

* It takes no parameters

*/

void myFunction()

{

}


Single line commenting should be used for class variables and for non trivial code within functions.


The program must also be accompanied by a report (report.pdf) on how it works, diagrams may be useful for this. Your report need only be a page long (3 pages max) and it must describe the technique you used to implement the virtual heap. It is not meant to be comprehensive documentation, but rather a proof that you understand the problem and its solution.

Note :


You MUST NOT use new , delete , malloc , calloc, or free in your program.



You are to use only the memory that has been allocated by v_heap.h ( char * vheap )

No STL containers are allowed. No static structs or objects allowed.


Tip :


You may find it useful to define a struct and use a struct pointer to index into the heap!