Using C++ code in C#

Question

I have c++ dll with class in wich I want to send string from C# code, surly I can't use string because of CLR, i'll stried to change string into char in c++ dll, and send byte from c#(because c++ char=byte in c#) but c# don't understand c++ array I can send 1 byte and it will be ok, but not array, please help! dll Code:

public ref class Coding
    {
    public:
        void HillCoding(char filePath[])
        {

            ...
        }
    };

At runtime with P/Invoke, the CLR will convert string into char * I believe — Richard J. Ross III
– Richard J. Ross III, Commented Nov 6, 2010 at 21:17
possible duplicate of Passing NON null-terminated strings to unmanaged code — Hogan
– Hogan, Commented Nov 6, 2010 at 21:18

Badiboy · Accepted Answer · 2010-11-06 21:50:42Z

1

Here is the working code of calling C++ dll function from C#:

    sbyte[] A_SB_array = new sbyte[0];
    ArrayConvCtoSB(ref A_SB_array, ar_param.ToCharArray());
    fixed (sbyte* SB_array = A_SB_array)
        return CPSFEW.getDataLength(SB_array);

It's not the "very good code" but it illustrate what you need.

PS: Here is ArrayConvCtoSB. I do not like it, it's just for understanding.

    static private void ArrayConvCtoSB(ref sbyte[] to_sbyte, char[] from_char)
    {
        for (int i = 0; i < from_char.Length; i++)
        {
            Array.Resize(ref to_sbyte, to_sbyte.Length + 1);
            to_sbyte[i] = (sbyte)from_char[i];
        }
    }

PPS: "fixed" is strongly required for forceing garbage collector not to clear the SB_array memory: otherwise it can. :)

answered Nov 6, 2010 at 21:50

Badiboy

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1 Comment

Badiboy Over a year ago

One more addition. Here is the declaration of getDataLength C++ function: "size_t getDataLength(const char *param) {...}"

Richard J. Ross III · Accepted Answer · 2010-11-06 21:19:38Z

1

Try this first, because CLR converts string to char *, no?:

callThisCPlusPlusMethod(myString)

If that doesn't work, Use

char[] sendArray = myString.ToCharArray();
callThisCPlusPlusMethod(sendArray);

Or, if needed in different encoding:

byte[] sendArray = Encoding.TheEncodingINeed.GetBytes(myString);
callThisCPlusPlusMethod(sendArray);

Note: I tend to like ambiguous names :)

answered Nov 6, 2010 at 21:19

Richard J. Ross III

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2 Comments

ZAA Over a year ago

Error 2 Argument 1: cannot convert from 'string' to 'std.basic_string<char,std.char_traits<char>,std::allocator<char> >*'

Richard J. Ross III Over a year ago

If your signature is the same as the one above, then theoretically that should work, I have no idea what the problem would be... did you try all the other methods I posted?

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