COM 输出指针在客户端中保持为空

Question

什么会导致 IEnumString->Next() 调用调用正确的函数但使客户端指针为空？一切都是 64 位 (Windows 10).

数据流：我的DLL -> MSSpellCheckingHost -> 客户端

In my code (Github link) everything checks out. The allocation and copy look fine. But the client sees a null pointer, but only when coming via ISpellCheckProvider->Suggest(); it works fine via ISpellCheckProviderFactory->get_SupportedLanguages()

摘自 EnumString.hpp 的片段：

template<typename String>
inline void CoCopyWString(const String& in, PWSTR* out) {
    debugp p(__FUNCTION__);
    p(in, static_cast<void*>(*out));
    *out = reinterpret_cast<LPWSTR>(CoTaskMemAlloc(sizeof(wchar_t)*(in.size() + 1)));
    std::copy(in.begin(), in.end(), *out);
    (*out)[in.size()] = 0;
    p(std::wstring(*out), static_cast<void*>(*out));
}

class EnumString : public IEnumString {
public:
...
    IFACEMETHODIMP Next(ULONG celt, LPOLESTR *rgelt, ULONG *pceltFetched) {
        debugp p(__FUNCTION__);
        p(celt);
        HRESULT hr = S_FALSE;

        ULONG i = 0;
        for (; i < celt && current < strings.size(); ++i, ++current) {
            p(i, current);
            CoCopyWString(strings[current], rgelt+i);
            p(static_cast<void*>(rgelt + i), static_cast<void*>(rgelt[i]));
        }

        if (celt > 1) {
            *pceltFetched = i;
        }
        if (i == celt) {
            hr = S_OK;
        }

        return hr;
    }
...
private:
    std::vector<std::wstring> strings;
    ULONG current = 0;
};

如图所示，有很多调试打印，因为将调试器附加到 MSSpellCheckingHost 是一件很烦人的事情，它们会产生预期的输出，例如：

EnumString::Next
    1
    0 0
    CoCopyWString
        i-llu 0000000000000000
        i-llu 000001CC35682AE0
    ~CoCopyWString
    000001CC356A1F50 000001CC35682AE0
~EnumString::Next

...这表明正在设置输出指针并且指向的数据是正确的。并且在使用SupportedLanguages is called - that returns the correct value to the enumerator and the value is used so it couldn't have been null. But when Suggest()时有效，结果没有通过。

通过 CoTaskMemAlloc 分配的 return 结构的所有其他功能也可以使用，因此主机总体上看起来是可用的，除了那个情况。

Answer 1

正如 Hans Passant 指出的那样，该片段

    if (celt > 1) {
        *pceltFetched = i;
    }

应该是

    if (pceltFetched) {
        *pceltFetched = i;
    }

COM 输出指针在客户端中保持为空

COM out-ptr remains null in client

c++

windows

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