How to call a C function from C# with a WCHAR* in parameter?

Question

I have the following C function

NTSTATUS
SendBuffer(
_In_ UINT32 Number,
_In_ PWCHAR wszBuffer
)

and the following c# method

[DllImport(@"cfunc.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "SendBuffer")]
    public static extern long SendBuffer(uint Number, [MarshalAsAttribute(UnmanagedType.LPWStr)] string wszBuffer);

and in c# i try to call the function with

string buffer = "one two treee";
SendBuffer((uint)x, buffer);

But i receive an System.AccessViolationException when i run the program. How can i fix this problem?

Thank you.

Does the `SendBuffer` function modify the string `wszBuffer`? If so, you need a `StringBuilder` not a `String`. — Cody Gray - on strike, Jun 02 '16 at 15:29
Check out http://stackoverflow.com/questions/6270525/sending-a-c-sharp-string-as-an-argument-to-a-unmanaged-c-dll-function — dbugger, Jun 02 '16 at 15:30
The C# return type `long` does not match the return type of the C function. Use the C# type `int` instead. — Ian Abbott, Jun 02 '16 at 17:13

score -1 · Answer 1 · answered Jun 02 '16 at 15:51

-1

A WChar is 16 bits so you need to send Uint16[]. See code below.

            string buffer = "one two treee";
            UInt16[] data = buffer.ToCharArray().Select(x => (UInt16)x).ToArray();

answered Jun 02 '16 at 15:51

jdweng

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How to call a C function from C# with a WCHAR* in parameter?

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