Pointer in API making life hell

[AAVarda]

Hello there.
There is a DLL file which contains a function as below. It will return me
the device name i.e pcDevName

ULONG MTMICRGetDevice (
DWORD dwDeviceContext ,
char *pcDevName
);

Example given to use the above function is as below
-----------------------------------------
#define DEVICE_NAME_LEN 128
int i=1;
DWORD dwResult;
char pcDevName[DEVICE_NAME_LEN] = "";
while ((dwResult =
MTMICRGetDevice (i,(char*)pcDev Name))!=MICR_ST _DEVICE_NOT_FOU ND
{
//Device found, increment the device number
i++;
}

My defination in VB .NET to get the pcDevName
--------------------------------------
Declare Auto Function fGetDeviceName Lib "mtmcrapi.d ll" Alias
"MTMICRGetDevic e" (ByVal intNum As Integer, ByRef strDName As Char) As
Integer

Private Sub cmdConnect_Clic k(ByVal sender As System.Object, ByVal e As
System.EventArg s) Handles cmdConnect.Clic k

Dim strMy As Char

Dim intI As Integer

Dim strRst As Integer

intI = 2

strRst = Win32.fGetDevic eName(intI, strMy)

MessageBox.Show (strMy.ToString , strRst.ToString )

End Sub

The function is returning the value 0 (that means ok) but the device name is
one char junk.
-WHAT IS WRONG???
-Is there a way to get the data by using the memory address in VB .NET

[Bart Mermuys]

Re: Pointer in API making life hell

Hi,

"AAVarda" <asgar@data-aware.com> wrote in message
news:OIBJlLY0FH A.2792@tk2msftn gp13.phx.gbl...[color=blue]
> Hello there.
> There is a DLL file which contains a function as below. It will return me
> the device name i.e pcDevName
>
> ULONG MTMICRGetDevice (
> DWORD dwDeviceContext ,
> char *pcDevName
> );
>
> Example given to use the above function is as below
> -----------------------------------------
> #define DEVICE_NAME_LEN 128
> int i=1;
> DWORD dwResult;
> char pcDevName[DEVICE_NAME_LEN] = "";
> while ((dwResult =
> MTMICRGetDevice (i,(char*)pcDev Name))!=MICR_ST _DEVICE_NOT_FOU ND
> {
> //Device found, increment the device number
> i++;
> }
>
> My defination in VB .NET to get the pcDevName
> --------------------------------------
> Declare Auto Function fGetDeviceName Lib "mtmcrapi.d ll" Alias
> "MTMICRGetDevic e" (ByVal intNum As Integer, ByRef strDName As Char) As
> Integer
>
> Private Sub cmdConnect_Clic k(ByVal sender As System.Object, ByVal e As
> System.EventArg s) Handles cmdConnect.Clic k
>
> Dim strMy As Char
>
> Dim intI As Integer
>
> Dim strRst As Integer
>
> intI = 2
>
> strRst = Win32.fGetDevic eName(intI, strMy)
>
> MessageBox.Show (strMy.ToString , strRst.ToString )
>
> End Sub
>
> The function is returning the value 0 (that means ok) but the device name
> is one char junk.
> -WHAT IS WRONG???
> -Is there a way to get the data by using the memory address in VB .NET
>[/color]

Try:
Imports System.Text

Declare Ansi Function fGetDeviceName Lib "mtmcrapi.d ll" Alias
"MTMICRGetDevic e" (ByVal Context As Integer, _
ByVal NameSB As StringBuilder) As Integer

Dim ret As Integer
Dim context As Integer
Dim nameSB As New StringBuilder(1 28)

context = 2
ret = Win32.fGetDevic eName( context, nameSB )

MessageBox.Show ( nameSB.ToString (), ret.ToString() )

hth,
Greetings

[AAVarda]

Re: Pointer in API making life hell

THANK YOU :) you guys are really really gr8. Problem solved
"Bart Mermuys" <bmermuys.nospa m@hotmail.com> wrote in message
news:ucSKtbY0FH A.1252@TK2MSFTN GP09.phx.gbl...[color=blue]
> Hi,
>
> "AAVarda" <asgar@data-aware.com> wrote in message
> news:OIBJlLY0FH A.2792@tk2msftn gp13.phx.gbl...[color=green]
>> Hello there.
>> There is a DLL file which contains a function as below. It will return me
>> the device name i.e pcDevName
>>
>> ULONG MTMICRGetDevice (
>> DWORD dwDeviceContext ,
>> char *pcDevName
>> );
>>
>> Example given to use the above function is as below
>> -----------------------------------------
>> #define DEVICE_NAME_LEN 128
>> int i=1;
>> DWORD dwResult;
>> char pcDevName[DEVICE_NAME_LEN] = "";
>> while ((dwResult =
>> MTMICRGetDevice (i,(char*)pcDev Name))!=MICR_ST _DEVICE_NOT_FOU ND
>> {
>> //Device found, increment the device number
>> i++;
>> }
>>
>> My defination in VB .NET to get the pcDevName
>> --------------------------------------
>> Declare Auto Function fGetDeviceName Lib "mtmcrapi.d ll" Alias
>> "MTMICRGetDevic e" (ByVal intNum As Integer, ByRef strDName As Char) As
>> Integer
>>
>> Private Sub cmdConnect_Clic k(ByVal sender As System.Object, ByVal e As
>> System.EventArg s) Handles cmdConnect.Clic k
>>
>> Dim strMy As Char
>>
>> Dim intI As Integer
>>
>> Dim strRst As Integer
>>
>> intI = 2
>>
>> strRst = Win32.fGetDevic eName(intI, strMy)
>>
>> MessageBox.Show (strMy.ToString , strRst.ToString )
>>
>> End Sub
>>
>> The function is returning the value 0 (that means ok) but the device name
>> is one char junk.
>> -WHAT IS WRONG???
>> -Is there a way to get the data by using the memory address in VB .NET
>>[/color]
>
> Try:
> Imports System.Text
>
> Declare Ansi Function fGetDeviceName Lib "mtmcrapi.d ll" Alias
> "MTMICRGetDevic e" (ByVal Context As Integer, _
> ByVal NameSB As StringBuilder) As Integer
>
> Dim ret As Integer
> Dim context As Integer
> Dim nameSB As New StringBuilder(1 28)
>
> context = 2
> ret = Win32.fGetDevic eName( context, nameSB )
>
> MessageBox.Show ( nameSB.ToString (), ret.ToString() )
>
> hth,
> Greetings
>[/color]

[Dragon]

Re: Pointer in API making life hell

Hello,
[color=blue]
> -WHAT IS WRONG???[/color]

Whong is that a char* in C is not exactly a *pointer to char*. It's a
*pointer to a null-terminated string*.
Thus, it should be declared as String in VB (or StringBuilder if it's
going to be changed) if you don't want to get a "one char junk".

You should try this:

~
Declare Function fGetDeviceName Lib "mtmcrapi.d ll" Alias
"MTMICRGetDevic e" ( _
ByVal dwDeviceContext As Integer, _
<MarshalAs(Unma nagedType.LPStr )> ByVal pcDevName As StringBuilder _
) As Integer
~
[color=blue]
> -Is there a way to get the data by using the memory address in VB .NET[/color]

Look at Shared Marshal.PtrTo* methods.
[color=blue]
>
>
>[/color]

Hope this helps,
Roman