C# - Calling unmanaged DLL from managed C# code.

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  • =?Utf-8?B?cmtwYXQ=?=
    #1

    C# - Calling unmanaged DLL from managed C# code.

    I have a DLL that i'm interfacing with that's in C++. here's the interface
    defn:
    SendCommand(voi d *h, char *cmd, char *data, char *respbuffer);

    here's the wrapper for the dll call in my C# code:
    [DllImport("test .dll", CharSet = CharSet.Ansi, EntryPoint = "SendComman d")]
    unsafe public static extern char* SendCommand(voi d* h,
    [MarshalAs(Unman agedType.LPStr)] string cmd, [MarshalAs(Unman agedType.LPStr)]
    string data, [MarshalAs(Unman agedType.LPArra y)] ref byte[] buffer);

    and here's my function call:


    //code here...
    byte buf = new byte[25];
    SendCommand(han dle, "cmd string", "data", buf);

    i think the cmd parameter is getting messed up when i marshal it as LPStr!!
    am i doing something wrong? the reason i say this is i do not get any
    response in the response buffer!!!

    i could get the same function call working in C++ and i do see the response
    in the buffer...can someone please help?
    Tags: None
    • Willy Denoyette [MVP]
      #2
      Re: C# - Calling unmanaged DLL from managed C# code.

      "rkpat" <rkpat@discussi ons.microsoft.c omwrote in message
      news:8F27EA3B-6B56-40D3-9B08-E6397824BABA@mi crosoft.com...
      >I have a DLL that i'm interfacing with that's in C++. here's the interface
      defn:
      SendCommand(voi d *h, char *cmd, char *data, char *respbuffer);
      >
      here's the wrapper for the dll call in my C# code:
      [DllImport("test .dll", CharSet = CharSet.Ansi, EntryPoint = "SendComman d")]
      unsafe public static extern char* SendCommand(voi d* h,
      [MarshalAs(Unman agedType.LPStr)] string cmd, [MarshalAs(Unman agedType.LPStr)]
      string data, [MarshalAs(Unman agedType.LPArra y)] ref byte[] buffer);
      >
      and here's my function call:
      >
      >
      //code here...
      byte buf = new byte[25];
      SendCommand(han dle, "cmd string", "data", buf);
      >
      i think the cmd parameter is getting messed up when i marshal it as LPStr!!
      am i doing something wrong? the reason i say this is i do not get any
      response in the response buffer!!!
      >
      i could get the same function call working in C++ and i do see the response
      in the buffer...can someone please help?


      Why the char* in :
      extern char* SendCommand
      there is no return defined in your C function.

      Try this:
      DllImport("test .dll", CharSet = CharSet.Ansi, EntryPoint = "SendComman d")]
      public static extern void SendCommand(Int Ptr h, string cmd, string data, StringBuilder
      buffer);

      IntPtr handle = ....;
      StringBuilder buf = new StringBuilder(2 5);
      SendCommand(han dle, ....);

      Willy.

        Comment

        • =?Utf-8?B?cmtwYXQ=?=
          #3
          Re: C# - Calling unmanaged DLL from managed C# code.

          thanks for the reply Willy.

          actually, the sendcommand function looks like this (my bad - typo)
          char * SendCommand(voi d *h, char *cmd, char *data, char *respbuffer);
          i'll try the recommended changes and will let u know how it goes. THANKS.


          "Willy Denoyette [MVP]" wrote:
          "rkpat" <rkpat@discussi ons.microsoft.c omwrote in message
          news:8F27EA3B-6B56-40D3-9B08-E6397824BABA@mi crosoft.com...
          I have a DLL that i'm interfacing with that's in C++. here's the interface
          defn:
          SendCommand(voi d *h, char *cmd, char *data, char *respbuffer);

          here's the wrapper for the dll call in my C# code:
          [DllImport("test .dll", CharSet = CharSet.Ansi, EntryPoint = "SendComman d")]
          unsafe public static extern char* SendCommand(voi d* h,
          [MarshalAs(Unman agedType.LPStr)] string cmd, [MarshalAs(Unman agedType.LPStr)]
          string data, [MarshalAs(Unman agedType.LPArra y)] ref byte[] buffer);

          and here's my function call:


          //code here...
          byte buf = new byte[25];
          SendCommand(han dle, "cmd string", "data", buf);

          i think the cmd parameter is getting messed up when i marshal it as LPStr!!
          am i doing something wrong? the reason i say this is i do not get any
          response in the response buffer!!!

          i could get the same function call working in C++ and i do see the response
          in the buffer...can someone please help?
          >
          >
          >
          Why the char* in :
          extern char* SendCommand
          there is no return defined in your C function.
          >
          Try this:
          DllImport("test .dll", CharSet = CharSet.Ansi, EntryPoint = "SendComman d")]
          public static extern void SendCommand(Int Ptr h, string cmd, string data, StringBuilder
          buffer);
          >
          IntPtr handle = ....;
          StringBuilder buf = new StringBuilder(2 5);
          SendCommand(han dle, ....);
          >
          Willy.
          >
          >

            Comment

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