Getting and Setting the Default Printer

- JanetTerra

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Liberty BASIC's Native Printer Dialog

The printerdialog function brings up the standard Windows printer dialog box. From the Liberty BASIC helpfile

• PRINTERDIALOG

• Description

• This command opens the standard Windows Common Printer Dialog. If the user chooses a printer and accepts, the next print job will go to this printer. Accepting a printer also sets the global variables PrinterName$, PrintCollate and PrintCopies to reflect what the user chose for the Printer Name, Collate and Copies. If no printer is accepted, then PrinterName$ is set to an empty string.

Unfortunately, Liberty BASIC doesn't interact well with Windows printer dialog. Despite what information PrinterName$ holds, all documents, whether text ( ldump lprint, dump ) or graphics ( vga , svga , xga ) will be sent to the default printer. A work-around is to set the desired printer as default before printing the document. This work-around is based upon contributions of Stefan Pendl. All of the code used in this article has been compiled from postings made by Stefan Pendl , both at Liberty BASIC Conforums and at the Official Liberty BASIC Support Group . The compiled snippets have been modified slightly for consistency with descriptive variable names, but otherwise remain intact.

The first step is to identify (get) the current default printer.

Get Default Printer

The information derived from the winspool.drv DLL will be placed in a struct. The struct must first be defined, here it's pcchBuffer , and the length of the struct element value set to _MAX_PATH. The call to the DLL is then made and the name of the default printer is placed into pcchBuffer.value.struct . Note that byRef is used so that the changes to currentDefaultPrinter$ are made both locally and globally. The function itself returns a number, 0 for a failure, non-zero for success.

 GetDefaultPrinter = GetDefaultPrinter(currentDefaultPrinter$) 
 if GetDefaultPrinter = 0 then 
 print "Call failed" 
 else 
 print "DefaultPrinter = ";currentDefaultPrinter$ 
 end if 
 end 
 
 function GetDefaultPrinter(byref currentDefaultPrinter$) 
 ' Returns zero if call fails 
 struct pcchBuffer, value as ulong 
 currentDefaultPrinter$ = space$(_MAX_PATH) 
 pcchBuffer.value.struct = _MAX_PATH 
 
 open "winspool.drv" for dll as #winspool 
 
 calldll #winspool, "GetDefaultPrinterA", _ 
 currentDefaultPrinter$ as ptr, _ 
 pcchBuffer as struct, _ 
 GetDefaultPrinter as long 
 
 close #winspool 
 end function 

Stefan's code has always been accompanied with an error catching routine. Should the call not work, Liberty BASIC can identify the cause of the failure.

 GetDefaultPrinter = GetDefaultPrinter(currentDefaultPrinter$) 
 if GetDefaultPrinter = 0 then 
 print "Call failed" 
 else 
 print "DefaultPrinter = ";currentDefaultPrinter$ 
 end if 
 end 
 
 function GetDefaultPrinter(byref currentDefaultPrinter$) 
 ' Returns zero if call fails 
 struct pcchBuffer, value as ulong 
 currentDefaultPrinter$ = space$(_MAX_PATH) 
 pcchBuffer.value.struct = _MAX_PATH 
 
 open "winspool.drv" for dll as #winspool 
 
 calldll #winspool, "GetDefaultPrinterA", _ 
 currentDefaultPrinter$ as ptr, _ 
 pcchBuffer as struct, _ 
 GetDefaultPrinter as long 
 if GetDefaultPrinter = 0 then 
 call DisplayError 
 else 
 currentDefaultPrinter$ = left$(currentDefaultPrinter$, pcchBuffer.value.struct - 1) 
 end if 
 close #winspool 
 end function 
 
 sub DisplayError 
 ErrorCode = GetLastError() 
 
 dwFlags = _FORMAT_MESSAGE_FROM_SYSTEM 
 nSize = 1024 
 lpBuffer$ = space$(nSize); chr$(0) 
 dwMessageID = ErrorCode 
 
 calldll #kernel32, "FormatMessageA", _ 
 dwFlags as ulong, _ 
 lpSource as ulong, _ 
 dwMessageID as ulong, _ 
 dwLanguageID as ulong, _ 
 lpBuffer$ as ptr, _ 
 nSize as ulong, _ 
 Arguments as ulong, _ 
 result as ulong 
 
 print "Error "; ErrorCode; ": "; left$(lpBuffer$, result) 
 end sub 
 
 function GetLastError() 
 calldll #kernel32, "GetLastError", _ 
 GetLastError as ulong 
 end function 

Storing the current default printer in a variable is important to allow that printer to be reassigned as default once the document has been printed.

List All Printers

The next step is to get a list of all available printers. This requires a little more work and three more structs. Stefan's function loops around to obtain all the printer names, until there are no names left. The printer names are concatenated, deliminated with a semicolon, in the string variable PrinterInfo$. The loop ends when error #122 (The data area passed to a system call is too small) is encounered. Once again, byRef is used so that PrinterInfo$ remains the same locally and globally.

Enumerating the printers requires allocating and searching blocks of memory, resulting in rather complex code. Also, listing printers available to the computer by a local (physical) connection requires different variables than listing printers available to the computer by a network or wireless connection. The EnumPrinters() function must be accessed twice, first for local printers then for network printers. The appropriate variables should be passed to the function each time.

• Flag to List Local Printers
• PRINTER.ENUM.LOCAL = hexdec("2")

• Flag to List Network Printers
• PRINTER.ENUM.CONNECTIONS = hexdec("4")

The first pass stores the retrieved information in LocalPrinterInfo$ and the second pass stores the retrieved information in NetworkPrinterInfo$ . These two stringes are then concatenated with a semicolon to hold all printers in PrinterInfo$ . Finally, an array is constructed to hold the individual printer names.

 ' Count and enumerate all printers 
 ' Need to access function twice, first for local printers, second for network printers 
 PRINTER.ENUM.LOCAL = hexdec("2") 
 PRINTER.ENUM.CONNECTIONS = hexdec("4") 
 
 nLocalPrinters = EnumPrinters(PrinterInfo$, PRINTER.ENUM.LOCAL) 
 print "nLocalPrinters = ";nLocalPrinters 
 LocalPrinterInfo$ = PrinterInfo$ 
 print "LocalPrinterInfo$ = ";LocalPrinterInfo$ 
 print 
 nNetworkPrinters = EnumPrinters(PrinterInfo$, PRINTER.ENUM.CONNECTIONS) 
 print "nNetworkPrinters = ";nNetworkPrinters 
 NetworkPrinterInfo$ = PrinterInfo$ 
 print "NetworkPrinterInfo$ = ";NetworkPrinterInfo$ 
 print 
 
 ' Add both to total and combine the 2 printer strings 
 nPrinters = nLocalPrinters + nNetworkPrinters 
 Print "nPrinters = ";nPrinters 
 PrinterInfo$ = LocalPrinterInfo$;";";NetworkPrinterInfo$ 
 print "PrinterInfo$ = ";PrinterInfo$ 
 
 ' Place all printers in an array 
 dim availablePrinters$(nPrinters) 
 for i = 1 to nPrinters 
 availablePrinters$(i) = word$(PrinterInfo$, i, ";") 
 next i 
 for i = 1 to nPrinters 
 print i, availablePrinters$(i) 
 next i 
 end 
 
 function EnumPrinters(byref PrinterInfo$, nFlags) 
 ' Returns the number of printers found 
 ' Fills the submitted variable with the printer names 
 ' Separated by semicolons (;) 
 open "winspool.drv" for dll as #winspool 
 struct pcbNeeded, value as ulong 
 struct pcReturned, value as ulong 
 struct PrinterInfo4, _ 
 pPrinterName$ as ptr, _ 
 pServerName$ as ptr, _ 
 Attributes as ulong 
 PrinterInfo4Len = len(PrinterInfo4.struct) 
 Level = 4 
 cbBuf = PrinterInfo4Len 
 uFlags = _LMEM_MOVEABLE or _LMEM_ZEROINIT 
 calldll #kernel32, "LocalAlloc", _ 
 uFlags as uLong, _ 
 cbBuf as uLong, _ 
 hMem as uLong 
 calldll #kernel32, "LocalLock", _ 
 hMem as uLong, _ 
 pBuffer as uLong 
 
 [retryEnumPrinters] 
 calldll #winspool, "EnumPrintersA", _ 
 nFlags as ulong, _ 
 PrinterName as ulong, _ 
 Level as ulong, _ 
 pBuffer as ulong, _ 
 cbBuf as ulong, _ 
 pcbNeeded as struct, _ 
 pcReturned as struct, _ 
 result as boolean 
 if result = 0 then 
 if GetLastError() = 122 then 
 cbBuf = pcbNeeded.value.struct 
 hOldMem = hMem 
 calldll #kernel32, "LocalReAlloc", _ 
 hOldMem as ulong, _ 
 cbBuf as ulong, _ 
 uFlags as ulong, _ 
 hMem as ulong 
 calldll #kernel32, "LocalLock", _ 
 hMem as uLong, _ 
 pBuffer as ulong 
 goto [retryEnumPrinters] 
 else 
 call DisplayError 
 end if 
 else 
 EnumPrinters = pcReturned.value.struct 
 BufferPointer = pBuffer 
 for count = 0 to EnumPrinters - 1 
 calldll #kernel32, "RtlMoveMemory", _ 
 PrinterInfo4 as struct, _ 
 BufferPointer as ulong, _ 
 PrinterInfo4Len as ulong, _ 
 result as void 
 BufferPointer = BufferPointer + PrinterInfo4Len 
 pointer = PrinterInfo4.pPrinterName$.struct 
 PrinterInfo$ = winstring(pointer); ";"; PrinterInfo$ 
 next count 
 PrinterInfo$ = left$(PrinterInfo$, len(PrinterInfo$)-1) 
 end if 
 calldll #kernel32, "LocalFree", _ 
 hMem as uLong, _ 
 result as uLong 
 close #winspool 
 end function 
 
 function GetLastError() 
 calldll #kernel32, "GetLastError", _ 
 GetLastError as ulong 
 end function 

The final step is to designate a different printer as default.

Set Default Printer

The code to set a default printer is the simplest of all, just passing a valid printer name to the winspool.drv dll. Like the GetDefaultPrinter() function, the SetDefaultPrinter() function returns a 0 for failure, a non-zero for success.

 selectedDefaultPrinter$ = "My Inkjet Printer" 
 ' Set new default printer 
 SetDefaultPrinter = SetDefaultPrinter(selectedDefaultPrinter$) 
 end 
 
 function SetDefaultPrinter(selectedDefaultPrinter$) 
 ' Returns zero if call fails 
 open "winspool.drv" for dll as #winspool 
 
 calldll #winspool, "SetDefaultPrinterA",_ 
 selectedDefaultPrinter$ as ptr,_ 
 SetDefaultPrinter as long 
 
 close #winspool 
 end function 

This is the same code, but with Stefan's error trapping included.

 selectedDefaultPrinter$ = "My Inkjet Printer" 
 ' Set new default printer 
 SetDefaultPrinter = SetDefaultPrinter(selectedDefaultPrinter$) 
 end 
 
 function SetDefaultPrinter(selectedDefaultPrinter$) 
 ' Returns zero if call fails 
 open "winspool.drv" for dll as #winspool 
 
 calldll #winspool, "SetDefaultPrinterA",_ 
 selectedDefaultPrinter$ as ptr,_ 
 SetDefaultPrinter as long 
 
 close #winspool 
 if SetDefaultPrinter = 0 then call DisplayError 
 end function 
 
 sub DisplayError 
 ErrorCode = GetLastError() 
 
 dwFlags = _FORMAT_MESSAGE_FROM_SYSTEM 
 nSize = 1024 
 lpBuffer$ = space$(nSize); chr$(0) 
 dwMessageID = ErrorCode 
 
 calldll #kernel32, "FormatMessageA", _ 
 dwFlags as ulong, _ 
 lpSource as ulong, _ 
 dwMessageID as ulong, _ 
 dwLanguageID as ulong, _ 
 lpBuffer$ as ptr, _ 
 nSize as ulong, _ 
 Arguments as ulong, _ 
 result as ulong 
 
 print "Error "; ErrorCode; ": "; left$(lpBuffer$, result) 
 end sub 
 
 function GetLastError() 
 calldll #kernel32, "GetLastError", _ 
 GetLastError as ulong 
 end function 

Getting, Listing, Setting the Default Printer (Mainwindow)

Using all three components, the programmer now has full control of getting, listing, and setting the default printer.

 ' Get the original default printer 
 GetDefaultPrinter = GetDefaultPrinter(origDefaultPrinter$) 
 print "origDefaultPrinter$ = ";origDefaultPrinter$ 
 print 
 
 ' Count and enumerate all printers 
 ' Need to access function twice, first for local printers, second for network printers 
 PRINTER.ENUM.LOCAL = hexdec("2") 
 PRINTER.ENUM.CONNECTIONS = hexdec("4") 
 
 nLocalPrinters = EnumPrinters(PrinterInfo$, PRINTER.ENUM.LOCAL) 
 print "nLocalPrinters = ";nLocalPrinters 
 LocalPrinterInfo$ = PrinterInfo$ 
 print "LocalPrinterInfo$ = ";LocalPrinterInfo$ 
 print 
 nNetworkPrinters = EnumPrinters(PrinterInfo$, PRINTER.ENUM.CONNECTIONS) 
 print "nNetworkPrinters = ";nNetworkPrinters 
 NetworkPrinterInfo$ = PrinterInfo$ 
 print "NetworkPrinterInfo$ = ";NetworkPrinterInfo$ 
 print 
 
 ' Add both to total and combine the 2 printer strings 
 nPrinters = nLocalPrinters + nNetworkPrinters 
 Print "nPrinters = ";nPrinters 
 PrinterInfo$ = LocalPrinterInfo$;";";NetworkPrinterInfo$ 
 print "PrinterInfo$ = ";PrinterInfo$ 
 
 ' Place all printers in an array 
 dim availablePrinters$(nPrinters) 
 for i = 1 to nPrinters 
 availablePrinters$(i) = word$(PrinterInfo$, i, ";") 
 next i 
 for i = 1 to nPrinters 
 print i, availablePrinters$(i) 
 next i 
 print 
 
 ' Select another default printer 
 Input "Printer to set as default > ";selectedDefaultPrinter 
 selectedDefaultPrinter$ = availablePrinters$(selectedDefaultPrinter) 
 print 
 
 ' Set new default printer 
 SetDefaultPrinter = SetDefaultPrinter(selectedDefaultPrinter$) 
 end 
 
 
 function EnumPrinters(byref PrinterInfo$, nFlags) 
 ' Returns the number of printers found 
 ' Fills the submitted variable with the printer names 
 ' Separated by semicolons (;) 
 open "winspool.drv" for dll as #winspool 
 struct pcbNeeded, value as ulong 
 struct pcReturned, value as ulong 
 struct PrinterInfo4, _ 
 pPrinterName$ as ptr, _ 
 pServerName$ as ptr, _ 
 Attributes as ulong 
 PrinterInfo4Len = len(PrinterInfo4.struct) 
 Level = 4 
 cbBuf = PrinterInfo4Len 
 uFlags = _LMEM_MOVEABLE or _LMEM_ZEROINIT 
 calldll #kernel32, "LocalAlloc", _ 
 uFlags as uLong, _ 
 cbBuf as uLong, _ 
 hMem as uLong 
 calldll #kernel32, "LocalLock", _ 
 hMem as uLong, _ 
 pBuffer as uLong 
 
 [retryEnumPrinters] 
 calldll #winspool, "EnumPrintersA", _ 
 nFlags as ulong, _ 
 PrinterName as ulong, _ 
 Level as ulong, _ 
 pBuffer as ulong, _ 
 cbBuf as ulong, _ 
 pcbNeeded as struct, _ 
 pcReturned as struct, _ 
 result as boolean 
 if result = 0 then 
 if GetLastError() = 122 then 
 cbBuf = pcbNeeded.value.struct 
 hOldMem = hMem 
 calldll #kernel32, "LocalReAlloc", _ 
 hOldMem as ulong, _ 
 cbBuf as ulong, _ 
 uFlags as ulong, _ 
 hMem as ulong 
 calldll #kernel32, "LocalLock", _ 
 hMem as uLong, _ 
 pBuffer as ulong 
 goto [retryEnumPrinters] 
 else 
 call DisplayError 
 end if 
 else 
 EnumPrinters = pcReturned.value.struct 
 BufferPointer = pBuffer 
 for count = 0 to EnumPrinters - 1 
 calldll #kernel32, "RtlMoveMemory", _ 
 PrinterInfo4 as struct, _ 
 BufferPointer as ulong, _ 
 PrinterInfo4Len as ulong, _ 
 result as void 
 BufferPointer = BufferPointer + PrinterInfo4Len 
 pointer = PrinterInfo4.pPrinterName$.struct 
 PrinterInfo$ = winstring(pointer); ";"; PrinterInfo$ 
 next count 
 PrinterInfo$ = left$(PrinterInfo$, len(PrinterInfo$)-1) 
 end if 
 calldll #kernel32, "LocalFree", _ 
 hMem as uLong, _ 
 result as uLong 
 close #winspool 
 end function 
 
 
 function GetDefaultPrinter(byref currentDefaultPrinter$) 
 ' Returns zero if call fails 
 
 struct pcchBuffer, value as ulong 
 currentDefaultPrinter$ = space$(_MAX_PATH) 
 pcchBuffer.value.struct = _MAX_PATH 
 
 open "winspool.drv" for dll as #winspool 
 
 calldll #winspool, "GetDefaultPrinterA", _ 
 currentDefaultPrinter$ as ptr, _ 
 pcchBuffer as struct, _ 
 GetDefaultPrinter as long 
 
 close #winspool 
 
 if GetDefaultPrinter = 0 then 
 call DisplayError 
 else 
 currentDefaultPrinter$ = left$(currentDefaultPrinter$, pcchBuffer.value.struct - 1) 
 end if 
 end function 
 
 function SetDefaultPrinter(selectedDefaultPrinter$) 
 ' Returns zero if call fails 
 open "winspool.drv" for dll as #winspool 
 
 calldll #winspool, "SetDefaultPrinterA",_ 
 selectedDefaultPrinter$ as ptr,_ 
 SetDefaultPrinter as long 
 
 close #winspool 
 if SetDefaultPrinter = 0 then call DisplayError 
 end function 
 
 sub DisplayError 
 ErrorCode = GetLastError() 
 
 dwFlags = _FORMAT_MESSAGE_FROM_SYSTEM 
 nSize = 1024 
 lpBuffer$ = space$(nSize); chr$(0) 
 dwMessageID = ErrorCode 
 
 calldll #kernel32, "FormatMessageA", _ 
 dwFlags as ulong, _ 
 lpSource as ulong, _ 
 dwMessageID as ulong, _ 
 dwLanguageID as ulong, _ 
 lpBuffer$ as ptr, _ 
 nSize as ulong, _ 
 Arguments as ulong, _ 
 result as ulong 
 
 print "Error "; ErrorCode; ": "; left$(lpBuffer$, result) 
 end sub 
 
 function GetLastError() 
 calldll #kernel32, "GetLastError", _ 
 GetLastError as ulong 
 end function 

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