64 位机器上的 DWORD 和 DWORD_PTR

2022-01-12 00:00:00 windows winapi mfc

为了支持 Win64 的 64 位寻址，向 Windows API 添加了一些 *_PTR 类型.

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 适用于 64 位和 32 位机器.

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，这个特定的 API 在 64 位机器上是否会失败.如何测试失败场景?

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

如果你传递一个 DWORD，函数不会失败，因为它适合 DWORD_PTR.但是，在 64 位平台上，可以保证指针适合 DWORD_PTR，但不适合 DWORD.

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，这段代码是正确的:

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.

但是这段代码是错误的，它会默默地将指针截断到它的低 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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