通过 Pinvoke 传递 C# 字符串

问题描述

C# 端:

    [DllImport(@"FileGuidUtils.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Unicode)]
    private static extern long getReparseType([MarshalAsAttribute(UnmanagedType.LPWStr)] string linkPath);

C/C++ 端:

__declspec(dllexport) ReparseType getReparseType(WCHAR *linkPath) {
    HANDLE hFile = CreateFile(linkPath, GENERIC_ALL, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT, NULL);
    if (hFile == INVALID_HANDLE_VALUE)
    {
        CloseHandle(hFile);
        return NEITHER;
    }

    REPARSE_DATA_BUFFER *reparseDataBuffer = (REPARSE_DATA_BUFFER *)malloc(MAXIMUM_REPARSE_DATA_BUFFER_SIZE);
    DWORD dwRetLen = 0;
    BOOL bRet = DeviceIoControl(hFile, FSCTL_GET_REPARSE_POINT, NULL, 0, reparseDataBuffer, MAXIMUM_REPARSE_DATA_BUFFER_SIZE, &dwRetLen, NULL);
    if (bRet == FALSE)
    {
        free(reparseDataBuffer);
        CloseHandle(hFile);
        return NEITHER;
    }

    ULONG reparseType = reparseDataBuffer->ReparseTag;
    free(reparseDataBuffer);
    CloseHandle(hFile);

    if (reparseType == IO_REPARSE_TAG_SYMLINK) {
        return SYMLINK;
    }
    else if (reparseType == IO_REPARSE_TAG_MOUNT_POINT) {
        return JUNCTION;
    }

    return NEITHER;
}

linkPath 是如何传递的?它是作为 malloc 字符串传递的，我需要在 C/C++ 端释放它还是 CLR 会为我处理它?如果它被清理干净，我是否正确传递了它?我可以将它作为没有 [MarshalAsAttribute(UnmanagedType.LPWStr)] 的普通 C# 字符串传递吗?谢谢！

How is linkPath passed? Is it passed as a malloc'd string and I need to free it up on the C/C++ side or will the CLR take care of it for me? If it is getting cleaned up, am I passing it correctly? Could I just pass it as an ordinary C# string without the [MarshalAsAttribute(UnmanagedType.LPWStr)]? Thanks!

推荐答案

C# 会为你复制一个 C# 字符串到非托管内存中，传递一个指向它的指针并在函数调用完成后删除该字符串

C# will make a copy of the C# string for you into unmanaged memory , pass a pointer to it and delete the string once the function call is finished

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