获取指针指向的内存大小方法
其实很简单，就是一个库函数
_msize
该函数返回在堆上分配的内存块大小，以字节为单位。因此将指针传递给这个函数就可以获取指针指向的内存大小了，不过该指针必须是动态分配的指针才行。
msdn的资料
size_t _msize( void *memblock );
| Routine | Required Header | Compatibility |
| _msize | <malloc.h> | Win 95, Win NT |
For additional compatibility information, see Compatibility in the Introduction.
Libraries
| LIBC.LIB | Single thread static library, retail version |
| LIBCMT.LIB | Multithread static library, retail version |
| MSVCRT.LIB | Import library for MSVCRT.DLL, retail version |
Return Value
_msize returns the size (in bytes) as an unsigned integer.
Parameter
memblock
Pointer to memory block
Remarks
The _msize function returns the size, in bytes, of the memory block allocated by a call to calloc, malloc, or realloc.