随便写写

最后，内存分配直接用realloc来实现，该函数签名如下：

void *realloc( void *memblock, size_t size );

 

对于释放内存则直接利用memmove函数来实现

Moves one buffer to another.

void *memmove( void *dest, const void *src, size_t count );

 

下段摘自MSDN

 

“

Return Value

Moves one buffer to another.

void *memmove( void *dest, const void *src, size_t count );

Return Value

memmove returns the value of dest.

Parameters

dest

Destination object

src

Source object

count

Number of bytes of characters to copy

Remarks

The memmove function copies count bytes of characters from src to dest. If some regions of the source area and the destination overlap, memmove ensures that the original source bytes in the overlapping region are copied before being overwritten.

”

 

“

realloc returns a void pointer to the reallocated (and possibly moved) memory block. The return value is NULL if the size is zero and the buffer argument is not NULL, or if there is not enough available memory to expand the block to the given size. In the first case, the original block is freed. In the second, the original block is unchanged. The return value points to a storage space that is guaranteed to be suitably aligned for storage of any type of object. To get a pointer to a type other than void, use a type cast on the return value.

Parameters

memblock

Pointer to previously allocated memory block

size

New size in bytes

Remarks

The realloc function changes the size of an allocated memory block. The memblock argument points to the beginning of the memory block. If memblock is NULL, realloc behaves the same way as malloc and allocates a new block of size bytes. If memblock is not NULL, it should be a pointer returned by a previous call to calloc, malloc, or realloc.

The size argument gives the new size of the block, in bytes. The contents of the block are unchanged up to the shorter of the new and old sizes, although the new block can be in a different location. Because the new block can be in a new memory location, the pointer returned by realloc is not guaranteed to be the pointer passed through the memblock argument.

realloc calls malloc in order to use the C++ _set_new_mode function to set the new handler mode. The new handler mode indicates whether, on failure, malloc is to call the new handler routine as set by _set_new_handler. By default, malloc does not call the new handler routine on failure to allocate memory. You can override this default behavior so that, when realloc fails to allocate memory, malloc calls the new handler routine in the same way that the new operator does when it fails for the same reason. To override the default, call

_set_new_mode(1) 

early in your program, or link with NEWMODE.OBJ.

When the application is linked with a debug version of the C run-time libraries, realloc resolves to _realloc_dbg. For more information about how the heap is managed during the debugging process, see Using C Run-Time Library Debugging Support.

”

 

有一点要注意，对于memblock为NULL的情况，该函数的作用与malloc一样，下面为sample：

 

 1: long *pBuffer;

 2:     long size;

 3:     pBuffer = (long *)malloc(2*sizeof(long));

 4:     *pBuffer = 1;

 5:     *(pBuffer+1)=2;

 6:  

 7:     long l1 = *(pBuffer+1);

 8:     size = _msize(pBuffer);

 9:     cout << "size:" << size << "\t" << (*pBuffer) << "\t" << l1 << endl;

 10:  

 11:     //realloc

 12:     realloc(pBuffer,3*sizeof(long));

 13:     *(pBuffer+2)=6;

 14:     l1 = *(pBuffer+1);

 15:     long l2 = *(pBuffer+2);

 16:     size = _msize(pBuffer);

 17:     cout << "size:" << size << "\t" << (*pBuffer) << "\t" << l1 << "\t" << l2 << endl;

 18:     memmove(pBuffer+1,pBuffer+2,sizeof(long));

 19:     

 20:     size = _msize(pBuffer);

 21:     l1 = *(pBuffer+1);

 22:     //l2 = *(pBuffer+2);

 23:     cout << "size:" << size << "\t" << (*pBuffer) <<  "\t" << l1 << "\t" << l2 << endl;