How to access a C++ function which takes pointers as input argument from a C#

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace PatternSequencer
{
    class Version
    {
        public string majorVersion;
        public string minorVersion;

        ushort* pmajorVersion;
        ushort* pminorVersion;
        ulong status;

        [DllImport(@"c:\DOcuments\Myapp.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "SRX_DllVersion")]
        public static extern ulong SRX_DllVersion(ushort* pmajorVersion, ushort* pminorVersion);


        public Version()
        {
            status = SRX_DllVersion(&pmajorVersion, &pminorVersion);
            if (status)
            {
                majorVersion = "1 - " + *pmajorVersion;
                minorVersion = "1 - " + *pminorVersion;
            }
            else
            {
                majorVersion = "0 - " + *pmajorVersion;
                minorVersion = "0 - " + *pminorVersion;
            }
        }
    }
}

It throws an Error Pointers and fixed size buffers may only be used in an unsafe context. How do I pass pointers to the C++ dll? I am new to C#, please help me

Answer 1

Rather than using an unsafe context try:

[DllImport(@"c:\FreeStyleBuild\BERTScope\Release\Bin\BitAlyzerDLL.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "SRX_DllVersion")]
public static extern ulong SRX_DllVersion(out ushort pmajorVersion, out ushort pminorVersion);

To make the call:

ushort major, minor;
SRX_DllVersion(out major, out minor);

I'm assuming the SRX_DllVersion parameters are output only, if not change out to ref.

Avoid unsafe code when ever possible.

Answer 2

Of course you've to mark the class unsafe to make it work.

unsafe class Version
{
    [DllImport(@"c:\FreeStyleBuild\BERTScope\Release\Bin\BitAlyzerDLL.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "SRX_DllVersion")]
     public static extern ulong SRX_DllVersion(ushort* pmajorVersion, ushort* pminorVersion);
}

If you have only one method you could mark the method as unsafe.

And don't forget to turn on "allow unsafe code" compiler option as well.

Answer 3

You must mark that method as unsafe

[DllImport(@"c:\FreeStyleBuild\BERTScope\Release\Bin\BitAlyzerDLL.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "SRX_DllVersion")]
public static extern ulong SRX_DllVersion(out ushort pmajorVersion, out ushort pminorVersion);