dmDeviceName is just 'c'

Question

I'm trying to get the names of each of my monitors using DEVMODE.dmDeviceName:

dmDeviceName
A zero-terminated character array that specifies the "friendly" name of the printer or display; for example, "PCL/HP LaserJet" in the case of PCL/HP LaserJet. This string is unique among device drivers. Note that this name may be truncated to fit in the dmDeviceName array.

I'm using the following code:

log.printf("Device Name: %s",currDevMode.dmDeviceName);

But for every monitor, the name is printed as just c. All other information from DEVMODE seems to print ok. What's going wrong?

Answer 1

Most likely you are using the Unicode version of the structure and thus are passing wide characters to printf. Since you use a format string that implies char data there is a mis-match.

The UTF-16 encoding results in every other byte being 0 for characters in the ASCII range and so printf thinks that the second byte of the first two byte character is actually a null-terminator.

This is the sort of problem that you get with printf which of course has no type-safety. Since you are using C++ it's probably worth switching to iostream based I/O.

However, if you want to use ANSI text, as you indicate in a comment, then the simplest solution is to use the ANSI DEVMODEA version of the struct and the corresponding A versions of the API functions, e.g. EnumDisplaySettingsA, DeviceCapabilitiesA.

Answer 2

dmDeviceName is TCHAR[] so if you're compiling for unicode, the first wide character will be interpreted as a 'c' followed by a zero terminator.

You will need to convert it to ascii or use unicode capable printing routines.