by Duncan Jones (19 Submissions)
Category: Windows API Call/Explanation
Compatability: Visual Basic 3.0
Difficulty: Advanced
Date Added: Wed 3rd February 2021
Rating: 
(3 Votes)
Shows how you can use the Windows API to return additional information about the printer above and beyond that which is available through the Visual Basic Printer object.
VBcoders 1. What the Printer object missed
Printing has long been a very problematic part of developing complete
and professional applications in Visual Basic. This was redressed to a large degree with the new Printer
object introduced in Visual Basic 4.
However, there are shortcomings with this object. The biggest shortcoming is that you cannot find out whether
the printer is ready, busy, out of paper etc. from your application.
However, there is an API call, GetPrinter which returns a great deal more information about a printer.
Private Declare Function GetPrinterApi Lib "winspool.drv" Alias _
"GetPrinterA" (ByVal hPrinter As Long, _
ByVal Level As Long, _
buffer As Long, _
ByVal pbSize As Long, _
pbSizeNeeded As Long) As Long
This takes the handle to a printer in hPrinter and fills
the buffer provided to it with information from the printer driver. To get the handle from the Printer object,
you need to use the OpenPrinter API call.
This handle must be released using the ClosePrinter API call as soon as you are finished with it.
Private Type PRINTER_DEFAULTS
pDatatype As String
pDevMode As DEVMODE
DesiredAccess As Long
End Type
Private Declare Function OpenPrinter Lib "winspool.drv" _
Alias "OpenPrinterA" (ByVal pPrinterName As String, _
phPrinter As Long, pDefault As PRINTER_DEFAULTS) As Long
Private Declare Function ClosePrinter Lib "winspool.drv" _
(ByVal hPrinter As Long) As Long
You pass the Printer.DeviceName to this to get the handle.
Dim lret As Long
Dim pDef As PRINTER_DEFAULTS
lret = OpenPrinter(Printer.DeviceName, mhPrinter, pDef)
2. The different statuses
There are a number of standard statuses that can be returned by the
printer driver.
Public Enum Printer_Status
PRINTER_STATUS_READY = &H0
PRINTER_STATUS_PAUSED = &H1
PRINTER_STATUS_ERROR = &H2
PRINTER_STATUS_PENDING_DELETION =
&H4
PRINTER_STATUS_PAPER_JAM = &H8
PRINTER_STATUS_PAPER_OUT =
&H10
PRINTER_STATUS_MANUAL_FEED =
&H20
PRINTER_STATUS_PAPER_PROBLEM =
&H40
PRINTER_STATUS_OFFLINE = &H80
PRINTER_STATUS_IO_ACTIVE =
&H100
PRINTER_STATUS_BUSY =
&H200
PRINTER_STATUS_PRINTING = &H400
PRINTER_STATUS_OUTPUT_BIN_FULL = &H800
PRINTER_STATUS_NOT_AVAILABLE =
&H1000
PRINTER_STATUS_WAITING = &H2000
PRINTER_STATUS_PROCESSING =
&H4000
PRINTER_STATUS_INITIALIZING =
&H8000
PRINTER_STATUS_WARMING_UP =
&H10000
PRINTER_STATUS_TONER_LOW =
&H20000
PRINTER_STATUS_NO_TONER =
&H40000
PRINTER_STATUS_PAGE_PUNT =
&H80000
PRINTER_STATUS_USER_INTERVENTION =
&H100000
PRINTER_STATUS_OUT_OF_MEMORY =
&H200000
PRINTER_STATUS_DOOR_OPEN =
&H400000
PRINTER_STATUS_SERVER_UNKNOWN =
&H800000
PRINTER_STATUS_POWER_SAVE =
&H1000000
End Enum
3. The data structures
As each printer driver is responsible for returning
this data there has to be a standard to which this returned data conforms
in order for one application to be able to query a number of different
types of printers. As it happens, there are nine different standard data
types that can be returned by the GetPrinter
API call in Windows 2000 (only the first two are universal to all current versions of Windows).
Of these, the second is the most interesting - named PRINTER_INFO_2
Private Type PRINTER_INFO_2
pServerName As String
pPrinterName As String
pShareName As String
pPortName As String
pDriverName As String
pComment As String
pLocation As String
pDevMode As Long
pSepFile As String
pPrintProcessor As String
pDatatype As String
pParameters As String
pSecurityDescriptor As Long
Attributes As Long
Priority As Long
DefaultPriority As Long
StartTime As Long
UntilTime As Long
Status As Long
JobsCount As Long
AveragePPM As Long
End Type
However, it is not as simple as just passing this structure to the GetPrinter API call as a printer can
return more information than is in that structure and if you do not allocate sufficent buffer space for it to
do so your application will crash.
Fortunately the API call caters for this - if you pass zero in the pbSize parameter then the API call will
tell you how big a buffer you will require in the pbSizeNeeded.
This means that filling the information from the printer driver becomes a two step process:
Dim lret As Long
Dim SizeNeeded As Long
Dim buffer() As Long
ReDim Preserve buffer(0 To 1) As Long
lret = GetPrinterApi(mhPrinter, Index, buffer(0), UBound(buffer), SizeNeeded)
ReDim Preserve buffer(0 To (SizeNeeded / 4) + 3) As Long
lret = GetPrinterApi(mhPrinter, Index, buffer(0), UBound(buffer) * 4, SizeNeeded)
However the buffer is just an array of Long data types. Some of the data within the PRINTER_INFO_2
data structure is String data. This must be collected from the addresses which are stored in the appropriate
buffer position.
To get a string from a pointer the CopyMemory API call is used and there is also an API call,
IsBadStringPtr, which can be used to verify that the address pointed to does actually contain a valid
string.
'\\ Memory manipulation routines
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)
'\\ Pointer validation in StringFromPointer
Private Declare Function IsBadStringPtrByLong Lib "kernel32" Alias "IsBadStringPtrA" (ByVal lpsz As Long, ByVal ucchMax As Long) As Long
Retrieving the string from a pointer is a common thing to have to do so it is worth having this utility function
in your arsenal.
Public Function StringFromPointer(lpString As Long, lMaxLength As Long) As String
Dim sRet As String
Dim lret As Long
If lpString = 0 Then
StringFromPointer = ""
Exit Function
End If
If IsBadStringPtrByLong(lpString, lMaxLength) Then
'\\ An error has occured - do not attempt to use this pointer
StringFromPointer = ""
Exit Function
End If
'\\ Pre-initialise the return string...
sRet = Space$(lMaxLength)
CopyMemory ByVal sRet, ByVal lpString, ByVal Len(sRet)
If Err.LastDllError = 0 Then
If InStr(sRet, Chr$(0)) > 0 Then
sRet = Left$(sRet, InStr(sRet, Chr$(0)) - 1)
End If
End If
StringFromPointer = sRet
End Function
So to use this to populate your PRINTER_INFO_2 variable:
With mPRINTER_INFO_2 '\\ This variable is of type PRINTER_INFO_2
.pServerName = StringFromPointer(buffer(0), 1024)
.pPrinterName = StringFromPointer(buffer(1), 1024)
.pShareName = StringFromPointer(buffer(2), 1024)
.pPortName = StringFromPointer(buffer(3), 1024)
.pDriverName = StringFromPointer(buffer(4), 1024)
.pComment = StringFromPointer(buffer(5), 1024)
.pLocation = StringFromPointer(buffer(6), 1024)
.pDevMode = buffer(7)
.pSepFile = StringFromPointer(buffer(8), 1024)
.pPrintProcessor = StringFromPointer(buffer(9), 1024)
.pDatatype = StringFromPointer(buffer(10), 1024)
.pParameters = StringFromPointer(buffer(11), 1024)
.pSecurityDescriptor = buffer(12)
.Attributes = buffer(13)
.Priority = buffer(14)
.DefaultPriority = buffer(15)
.StartTime = buffer(16)
.UntilTime = buffer(17)
.Status = buffer(18)
.JobsCount = buffer(19)
.AveragePPM = buffer(20)
End With
The complete source code for these examples is available for download
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