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DDE in C# .NET
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M K via .Net Guru (VIP)
I've got this code:
(Library GMDDE.dll)
namespace GMDDE {
delegate Int32 DDECall(Int32 uiType, Int32 uiFmt, Int32 hConv,
    Int32 sz1, Int32 sz2, Int32 hData, Int32 lData1, Int32 lData2);
    public class GMDDEClass {
        [DllImport("user32", EntryPoint="DdeInitializeA")]
        private static extern Int32 DdeInitialize(Int32 pidInst, DDECall pfnCallback,
            Int32 afCmd, Int32 ulRes);
        private const Int32 DMLERR_NO_ERROR = 0x0000;
        private const Int32 APPCMD_CLIENTONLY = 0x00000010;
        public bool InitDDE(Int32 hConv, Int32 lIdLocal) {
            DDECall GMDDEDelegat = new DDECall(DDECallback);
            if (DdeInitialize(lIdLocal, GMDDEDelegat, APPCMD_CLIENTONLY, 0) != DMLERR_NO_ERROR) {
                return false;
            }
            else {
                return true;
            }
        }
        public static Int32 DDECallback(Int32 uiType, Int32 uiFmt, Int32 hConv,
            Int32 sz1, Int32 sz2, Int32 hData, Int32 lData1, Int32 lData2) {
            return 1;
        }
    }
}
and here is calling in another project:
(application ProdCat.exe)
...
GMDDE.GMDDEClass GMDDEInstance = new GMDDE.GMDDEClass();
            Int32 hConv = 0;
            Int32 lIdLocal = 0;
            if (GMDDEInstance.InitDDE(hConv, lIdLocal) == false) {
                MessageBox.Show("Wyst?pi? b??d podczas inicjalizacji DDE!",
                    "B??d inicjalizacji DDE",
                    MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            else {
                MessageBox.Show("Inicjalizacja DDE powiod?a si?!",
                    "DDE zainicjowane",
                    MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
...
Compilation is successfull, but I get an exception:
System.NullReferenceException in GMDDE.dll (line: ...DDEInitialize...)

Where I make a mistake?
--------------------------------
From: M K

-----------------------
Posted by a user from .Net Guru (http://www.dot-net-guru.com/)

<Id>2M1SkVqmckmvG826tVif0A==</Id>
Reply to this message...
 
    
Ben Schwehn
M K via .Net Guru wrote:
[Original message clipped]

I believe the mistake is that DdeInitialize takes an pointer to an int,
not an int. You're then passing NULL as the pointervalue (Int32 lIdLocal
= 0;)
when the doc says that: At initialization, this parameter should
*point* to 0.

hth
--
Ben
http://bschwehn.de
Reply to this message...
 
 
System.NullReferenceException
System.Windows.Forms.MessageBox
System.Windows.Forms.MessageBoxButtons
System.Windows.Forms.MessageBoxIcon




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