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#1 Posted : Saturday, 14 November 2009 3:37:51 AM(UTC)

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Joined: 23/11/2008(UTC)
Posts: 523

Call unmanaged code with int* or char* using simple DllImport

As discussed in How to call native C/C++ functions with pointers' parameters from C#, we can use Platform Invoke or DllImport to call native/unmanaged code with flat C API from a .NET application (eg. in C#).

P/Invoke can be very simple when only the isomorphic types are used as parameters in the exported functions of the native dll. The isomorphic types such as "int" in C# and C++ is identical. However, when the parameters of the function involve non-isomorhic types such as char* or int*, we need to do a bit more. For example, for char*, we must allocate char* buffer and receive string by pointer, we cannot use UnmanagedType.LPStr attribute, so we pass ANSI string as byte array. int* is more simple because it's 1-element Int32 array. See the following example:

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

namespace ConsoleApplication1
    class Program
        [DllImport("decrypt.dll", EntryPoint = "_GetSerialRegData"/*, 
          ExactSpelling = false*/,SetLastError=true)]
        static extern void GetSerialRegData(
          [MarshalAs(UnmanagedType.LPArray)] Int32[] Salt, 
          [MarshalAs(UnmanagedType.LPArray)] byte[] SerialNo, 
          [MarshalAs(UnmanagedType.LPArray)] byte[] ModId, 
          [MarshalAs(UnmanagedType.LPArray)] Int32[] Days, 
          [MarshalAs(UnmanagedType.LPArray)] Int32[] Qty, string SCode);

        public static void Main(string[] args)
            byte[] SerialNo = new byte[6];
            byte[] ModId = new byte[6];
            Int32[] Salt = new Int32[1];
            Int32[] Days = new Int32[1];
            Int32[] Qty = new Int32[1];

            Salt[0] = 0;
            Days[0] = 0;
            Qty[0] = 0;

            string SCode = "BKXP8T3BXVRWUSAV77FDG";
            GetSerialRegData(Salt, SerialNo, ModId, Days, Qty, SCode);

            string strSerial = System.Text.Encoding.ASCII.GetString(SerialNo);
            string strModId = System.Text.Encoding.ASCII.GetString(ModId);
            int nSalt = Salt[0];
            int nDays = Days[0];
            int nQty = Qty[0];


In the example, I allocated 6 bytes for receiving each ANSI string, one element in Int32 array. For receiving string from byte array I used Text.Encoding.ASCII class.

Edited by user Tuesday, 4 December 2018 7:50:48 AM(UTC)  | Reason: Not specified

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