The usual way to launch a file is to use Shell­Execute, which opens the file in the default program registered to handle that type of file. But what if you want to override the default?

We saw some time ago that if you know the ProgId of the program you want to run, you can specify it in the lpClass of the SHELL­EXECUTE­INFO to force the file to be treated as if it were a specific kind of file.

Okay, but what if you aren’t sure that the program you want to run has registered a ProgId at all? Or if you don’t know what that ProgId is? For example, maybe you searched the hard drive for executable files and put them all in a list, and let the user pick one, and then you want to run that program to open the file.

In that case, you are in a bit of a pickle because you don’t know how an arbitrary program expects its command line to be formatted in order to open a file. Fortunately, most programs which can open files will accept the file name on the command line with no other options, so you will have a high chance of success if you simply enclose the name of the file you want to open in quotation marks (in case it contains spaces), and then pass that as the command line. When calling Shell­Execute, you pass lpFile equal to the program you want to run, and lpParameters equal to the file you want to open, enclosed in quotation marks if necessary.

Exercise: Does the path to the program need to be fully-qualified?

Exercise: Why do you have to quote the file you want to open, but not the program itself?

One reason you may want to use Shell­Execute instead of just going straight to Create­Process is if you need elevation. You can pass lpOperation equal to runas to get Shell­Execute to do the work of prompting the user for elevation.