c/c++如何判断指针无效？如NULL,0xcccccccc,0xfeeefeee,野指针等

c/c++如何判断指针无效？不仅仅是NULL的判断，有时由于指针释放没有赋NULL，指针会变成野指针或诸如0xcccccccc,0xfeeefeee形式的无效指针，那么此时如何判断指针是否有效呢？

AfxIsValidAddress

// Allocate a 5 character array, which should have a valid memory address.
char* arr = new char[5];

// Create a null pointer, which should be an invalid memory address.
char* null = (char*)0x0;

ASSERT(AfxIsValidAddress(arr, 5));
ASSERT(!AfxIsValidAddress(null, 5));

IsBadWritePtr, IsBadReadPtr

BOOL AFXAPI AfxIsValidAddress(const void* lp, UINT nBytes,
BOOL bReadWrite /* = TRUE */)
{
// simple version using Win-32 APIs for pointer validation.
return (lp != NULL && !IsBadReadPtr(lp, nBytes) &&
(!bReadWrite || !IsBadWritePtr((LPVOID)lp, nBytes)));
}