GlobalMem issues

[Steven Pringels 3]

Strange things in the land of globalmem...

The underlying code works in application A but not in application B
Especially the Poke$ doesn't work in another application. The calls are the
same.

Function malloc(ByVal sData As String) As Dword

 Local vStr   As Dword ' String Ptr
 Local hPtr   As Long
 Local hLock  As Long

 If IsFalse(Len(sData)) Then
    Function = 0
    Exit Function
 End If

 GlobalMem Alloc Len(sData) to hPtr

 GlobalMem Lock hPtr To vStr

 ' Need to use string pointer to allocate the string data instead of @vstr = sData (Bugfix)
 '@vStr = sData
 ' vStr = StrPtr(sData)
 Poke$ vStr, sData

 GlobalMem Unlock hPtr To hLock

 Function = hPtr

End Function

In application B where above mentioned codesnippet doesn't work, this will but then this code won't work in application A.

Function malloc(ByVal sData As String) As Dword

 Local vStr   As String ptr
 Local hPtr   As Long
 Local hLock  As Long

 If IsFalse(Len(sData)) Then
    Function = 0
    Exit Function
 End If

 GlobalMem Alloc Len(sData) to hPtr

 GlobalMem Lock hPtr To vStr

 'Poke$ vStr, sData
 @vStr = sData


 '@vStr = sData
 GlobalMem Unlock hPtr To hLock

 Function = hPtr

End Function

I going nuts over this. ...

I want a general wrapper for global mem function that will work in every application.

[Michael Mattias]

What do you want in your memory block? The STRING PTR? The string data?

If you want the STRING PTR

LOCAL vStr AS STRING PTR, dwAddr AS DWORD
  GLOBALMEM ALLOC  SIZEOF(vStr) TO hMem
  GLOBALMEM LOCK hMem  to dwAddr
  POKE LONG, dwAddr, VARPTR(sData))

If you want the string data

LOCAL dwAddr AS DWORD
   GLOBAL MEM ALLOC  LEN(sData)  TO hMem
   GLOBAL MEM LOCK   hMem to  dwADDR 
   POKE$   dwAddr, sData
...

I suppose you might want a pointer to the string data (not the same as a STRING PTR). Exercise left to user.

BTW, I think I'd avoid using "malloc" as a function name for a function which does more than allocate memory and return an address, as "malloc" is a c-language keyword for same and often appears in examples of WinAPI usage on MSDN.


Ref: malloc, realloc, free for PB/Win32 September 20, 2002

[Steven Pringels 3]

Hi Michael,

Yes, I want the string data and it is exactly that what I'm doing.

LOCAL dwAddr AS DWORD
   GLOBAL MEM ALLOC  LEN(sData)  TO hMem
   GLOBAL MEM LOCK   hMem to  dwADDR 
   POKE$   dwAddr, sData

This code above crash my program... but the following does not.

 Local vStr   As String ptr
 Local hPtr   As Long
 Local hLock  As Long

 If IsFalse(Len(sData)) Then
    Function = 0
    Exit Function
 End If

 GlobalMem Alloc Len(sData) to hPtr

 If hPtr Then

     GlobalMem Lock hPtr To vStr

     @vStr = sData

     GlobalMem Unlock hPtr To hLock

     Function = hPtr

 End If

End Function

So, even though I'm using String Ptr, I'm assigning the sData to the location at which Global Mem locked the memory.

[Michael Mattias]

FUNCTION Foo() AS LONG

 LOCAL dwAddr AS DWORD, sData AS STRING, hMem AS LONG
   
   sData = "foo"
   
   GLOBALMEM ALLOC  LEN(sData)  TO hMem
   GLOBALMEM LOCK   hMem TO  dwADDR
   POKE$   dwAddr, sData
   
END FUNCTION

Runs here without incident (Not that it does anything).

Methinks your problem is elsewhere in your program.

[Steven Pringels 3]

To MCM - You were right

Michael, obviously you were right. A lot of times actually

The problem was not the malloc function even though trace did stop there...
it was the function to get the value back (i use memstr).

The function looks like this It is the corrected version.
I used a string ptr to get the data back from a Poke$ which is of course wrong. I corrected it with a Asciiz Ptr and this is the way to go.

Thanks !

Function memstr(ByVal hPtr As Dword) As String

 Local vStr   As AsciiZ Ptr 'String Ptr
 Local hLock  As Dword

 GlobalMem Lock hPtr To vStr

 Function = Rtrim$(@vStr, Chr$(0))

 GlobalMem Unlock hPtr To hLock

End Function