C# - call function from dynamic library dll

njz Published at Dev

njz

I have to access dynamic library using C#. It works great when using COM library however when I try to use Dynamic library, it causing error.

1st problem

At first i do my code like this:

[DllImport("mydll.dll")]
public static extern int toGetInfo(uint id, char[] strVolume, char[] strInfo);
// strVolume and strInfo is parameter that return value with [out]

public static void Main()
{
char[] test1,test2;
toGetInfo(0,test1,test2);
}

But it unable to compile with error use of unassigned local variable for test1 and test2 . Then I edit my code by adding out like this:

[DllImport("mydll.dll")]
public static extern int toGetInfo(uint id, out char[] strVolume, out char[] strInfo);
// strVolume and strInfo is parameter that return [out]

public static void Main()
{
char[] test1,test2;
toGetInfo(0, out test1, out test2);
}

It able to compile but returns null value to test1 and test2.

2nd problem

[DllImport("mydll.dll")]
public static extern int toOpen(uint id, char* name);

 public static void Main()
{
 char name;
 toOpen(0, name);
}

When compile it give error "Pointers and fixed size buffers may only be used in an unsafe context"

Any idea how to do it?

jdweng

Try following :

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


namespace ConsoleApplication74
{
    class Program
    {
        [DllImport("mydll.dll")]
        public static extern int toGetInfo(uint id, IntPtr strVolume, IntPtr strInfo);

        [DllImport("mydll.dll")]
        public static extern int toOpen(uint id, IntPtr name);

        const int STRING_LENGTH = 256;
        static void Main(string[] args)
        {

            IntPtr strVolumePtr = Marshal.AllocHGlobal(STRING_LENGTH);
            IntPtr strInfoPtr = Marshal.AllocHGlobal(STRING_LENGTH);

            uint id = 123;

            int status1 = toGetInfo(id, strVolumePtr, strInfoPtr);

            string strVolume = Marshal.PtrToStringAnsi(strVolumePtr);
            string strInfo = Marshal.PtrToStringAnsi(strInfoPtr);

            string name = "John";
            IntPtr openNamePtr = Marshal.StringToHGlobalAnsi(name);
            int status2 = toOpen(id, openNamePtr);

            Marshal.FreeHGlobal(strVolumePtr);
            Marshal.FreeHGlobal(strInfoPtr);
            Marshal.FreeHGlobal(openNamePtr);

        }

    }

}

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