Windows 7 Default Printer Not Detected

3
votes

I have an application that uses an old reporting library (ReportPro). On Windows 7 64, it sometimes fails to find the default printer. I did some digging and found the problem in the windows registry. ReportPro determines the available printers via the GetProfileString windows API. It gets a list of available printers from here:

HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Devices

It gets the default printer from here:

HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows\Device

What I'm seeing in the windows registry is the the list of printers will show the name and the network port we are using as: 

HP LaserJet 5200 Series PCL 5 on Ne03:
Microsoft XPS Document Writer on Ne01:
HP Officejet Pro K8600 Series on Ne02:
Phaser 8860-2 PS on Ne00:
CutePDF Writer on CPW2:

On some systems the value of the default printer string is different. It would be something like:

HP LaserJet 5200 Series PCL 5 on Ne01:

In particular the NExx number is different in the default printer value compared to the list of printers.

The report package fails to find a default printer as it uses the printer name and the NExx number in the comparison.

Why would the NExx values be different and how do I make sure the values "stick"? The solution I have found for the moment is to set a different printer as default and then choose the correct default printer. That seems to resolve the problem temporarily but it is not permanent.

This problems seems to be Win7 only. Several of the XP machines have never had this problem in the last 8 years.

1
windowsdelphiprinting
Playing around in the registry, it would appear that the first defined printer in the string is the user default. You can also validate that against the integer value on the "UserSelectedDefault" registry value in the same Key. - LaKraven
Microsoft documents the "Nexx:" naming here: [link]technet.microsoft.com/en-us/library/cc775625(v=ws.10).aspx When the printer is a local printer, port is the name of the port to which it is connected; for example, LPT1. Otherwise, port is Nexx, where xx is a numeric value, starting with 00. This latter format is used for printers that are access through the network, for local printers with ports that begin with \\, when the port name has a space in it, and when the name of the port has a length greater than five. - Craig Lebakken
It's not guaranteed that the first defined printer is the default. I've looked at several different machines and it varies quite a bit. - Hugh
I never really got a good answer as to why the port would have different values in the two registry locations. What I ended up doing is change the report library to ignore the port number and use only the printer name when trying to determine the default printer. Printer names are unique anyway. This is not the ideal solution but will work until we replace the library. - Hugh

1 Answers

2
votes

The recommended method for retrieving the default printer is to use the Windows API GetDefaultPrinter() API rather than reading the registry. The recommended method for retrieving the list of all printers is to use EnumPrinters(). If you modify your code to use the Windows APIs instead of directly reading the registry, it should work reliably on Windows 7.