How can I import C++ DLL function using p/invoke into C#?

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i have this function in c++ which defined in header file

C++

MYDLL_API BOOL GetFolderSize(LPCTSTR lpszStartFolder, 
               BOOL bRecurse, 
               BOOL bQuickSize,
               PLARGE_INTEGER lpFolderSize,
               LPDWORD lpFolderCount /*= NULL*/,
               LPDWORD lpFileCount /*= NULL*/);

where MYDLL_API is defined as

C++

#ifdef MYDLL_EXPORTS
#define MYDLL_API __declspec(dllexport)
#else
#define MYDLL_API __declspec(dllimport)
#endif

after compile it as DLL project
i create c# declaration for this function as this

C#

[StructLayout(LayoutKind.Explicit, Size = 8)]
    struct LARGE_INTEGER
    {
        [FieldOffset(0)]
        public Int64 QuadPart;
        [FieldOffset(0)]
        public UInt32 LowPart;
        [FieldOffset(4)]
        public Int32 HighPart;
    }

  [DllImport("mydll.dll")]
    extern static bool GetFolderSize(string lpszStartFolder,
                               bool bRecurse,
                               bool bQuickSize,
                               out LARGE_INTEGER lpFolderSize,
                                out UInt32 lpFolderCount,
                                out UInt32 lpFileCount);

in run time it did not give an exception but it return false (mean that the function is failed )
why ? is the reason because of complicated data type in c++ (PLARGE_INTEGER)
or what ??
thanks

What I have tried:

i have try this

[StructLayout(LayoutKind.Explicit, Size = 8)]
struct LARGE_INTEGER
{
[FieldOffset(0)]
public Int64 QuadPart;
[FieldOffset(0)]
public UInt32 LowPart;
[FieldOffset(4)]
public Int32 HighPart;
}

[DllImport("mydll.dll")]
extern static bool GetFolderSize(string lpszStartFolder,
bool bRecurse,
bool bQuickSize,
out LARGE_INTEGER lpFolderSize,
out UInt32 lpFolderCount,
out UInt32 lpFileCount);

Posted 3-Oct-16 7:13am

nieo

Updated 3-Oct-16 8:04am

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Comments

Richard MacCutchan 3-Oct-16 13:35pm

The only way to know the answer is by using the debugger. We do not know what values you are passing in to the function, or why it is returning false.

2 solutions

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Gregory Haberek · Answer 1 · 2016-10-03T08:03:00

The library you're calling is using cdecl calling convention, but the default for C# is winapi, a.k.a. stdcall. Change your DllImport call to look like this instead:

C#

[DllImport("mydll.dll"), CallingConvention=CallingConvention.Cdecl)]
extern static bool GetFolderSize(string lpszStartFolder,
    bool bRecurse,
    bool bQuickSize,
    out LARGE_INTEGER lpFolderSize,
    out UInt32 lpFolderCount,
    out UInt32 lpFileCount);

#realJSOP · Answer 2 · 2016-10-03T08:04:00

Solution 2

0) Make double-damn sure your method prototype is correct.

1) Change the "out" parameters to "output".

2) Why are you calling an unmanaged DLL to do that when .Net provides exactly the same functionality?

Posted 3-Oct-16 8:04am

#realJSOP

Updated 3-Oct-16 8:06am

v2