64位计算机上的DWORD和DWORD_PTR [英] DWORD and DWORD_PTR on 64 bit machine

问题描述

为支持Win64的64位寻址，很少将*_PTR类型添加到Windows API中.

There are few *_PTR types added to the Windows API in order to support Win64's 64bit addressing.

SetItemData(int nIndex,DWORD_PTR dwItemData)

当我将第二个参数作为DWORD传递时，此API可同时用于64位和32位计算机.

This API works for both 64 and 32 bit machines when I pass second parameter as DWORD.

我想知道，如果我将第二个参数作为DWORD传递，那么这个特定的API是否会在64位计算机上失败.如何测试失败情况?

I want to know, if this particular API will fail on 64 bit machine, if I pass the second parameter as DWORD. How can I test the fail scenario?

谢谢， 尼基尔

推荐答案

如果您传递DWORD，则该函数不会失败，因为它适合DWORD_PTR.但是，在64位平台上，一定要保证指针适合DWORD_PTR而不适合 .

The function will not fail if you pass a DWORD, because it fits into a DWORD_PTR. A pointer, however, is guaranteed to fit into a DWORD_PTR but not into a DWORD on 64-bit platforms.

因此，此代码是正确的:

Thus, this code is correct:

int *before_ptr = new int;
yourListBox.SetItemData(index, (DWORD_PTR) before_ptr);
int *after_ptr = (int *) yourListBox.GetItemData(index);
ASSERT(before_ptr == after_ptr);  // Succeeds.
delete after_ptr;                 // Works.

但是此代码是错误的，它将以无提示的方式将指针截断到其低32位:

But this code is wrong and will silently truncate the pointer to its lower 32 bits:

int *before_ptr = new int;
yourListBox.SetItemData(index, (DWORD) before_ptr);
int *after_ptr = (int *) yourListBox.GetItemData(index);
ASSERT(before_ptr == after_ptr);  // Fails.
delete after_ptr;                 // Undefined behavior, might corrupt the heap.

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