Using C++ method in c#

Question

I'm writing a c# console application that uses a C++ class library. In C++ language class library I have a method:

public:bool GetMDC(char fileName[], char mdcStrOut[]){
    // My Code goes Here
}

This method gets a file path in fileName parameter and puts a value in mdcStrOut.

I add this class library as reference to my C# console application. when I want to call GetMDC method the method needs two sbyte parameters. So it's signature in c# is GetMDC(sbyte* fileName, sbyte* mdcStrOut).

My code looks like this:

unsafe{
    byte[] bytes = Encoding.ASCII.GetBytes(fileName);
    var _mdc = new TelsaMDC.TelsaMDCDetection();
    var outPut = new sbyte();
    fixed (byte* p = bytes)
    {
        var sp = (sbyte*)p;
        //SP is now what you want
        _mdc.GetMDC(sp, &outPut);
    }
}

It works without error. But the problem is that outPut variable only contains the first character of mdcStrOut. I'm unfamiliar with C++. I know that I'm passing the memory address of output to the GetMDC. So how can I get the value of it in my console application?

EDIT

when I declare output variable like this var outPut = new sbyte[MaxLength] I get an error on _mdc.GetMDC(sp, &outPut); line on the & sign. It says: Cannot take the address of, get the size of, or declare a pointer to a managed type ('sbyte[]')

Andrey Nasonov · Accepted Answer · 2015-09-27 14:18:06Z

1

The variable outPut is a single byte. You need to create a receive buffer, for example, var outPut = new sbyte[MaxLength].

unsafe{
    byte[] bytes = Encoding.ASCII.GetBytes(fileName);
    var _mdc = new TelsaMDC.TelsaMDCDetection();
    var outPut = new sbyte[256];  // Bad practice. Avoid using this!
    fixed (byte* p = bytes, p2 = outPut)
    {
        var sp = (sbyte*)p;
        var sp2 = (sbyte*)p2;
        //SP is now what you want
        _mdc.GetMDC(sp, sp2);
    }
}

Also, I recommend to rewrite the code to avoid possible buffer overflow because the function GetMDC does not know the size of the buffer.

edited Sep 27, 2015 at 14:18

answered Sep 27, 2015 at 14:04

Andrey Nasonov

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1 Comment

Andrey Nasonov Over a year ago

Just do it the same way as the first parameter bytes

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