Calling c++ (dll) from c# with an LPCTSTR parameter

An example of calling a c++ dll from c#.

First, some simple c++ code.

test.h

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extern "C" __declspec(dllexport) int test(LPCTSTR szFileName);

test.cpp

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int test(LPCTSTR szFileName) {
     return 0;
}

Next, the c# side

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[DllImport("sampleLib.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern int test( [MarshalAs(UnmanagedType.LPWStr)] string szFileName);

private void button2_Click(object sender, EventArgs e)
{
    string szFileName = @"c:\filename.txt";
    int result = test(ticketName);
    Debug.WriteLine("test=" + result);
}

CallingConvention = CallingConvention.Cdecl and [MarshalAs(UnmanagedType.LPWStr)] are the important parts.

The other way around, receiving a string from c++: take it as IntPtr and do this.

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IntPtr ptr = test("111111");
string data = Marshal.PtrToStringAnsi(ptr);
// 꼭 해제 한다
Marshal.FreeHGlobal(data);