I want to use CDT parser in a project. The project would be a command-line, stand-alone project, i.e., not an Eclipse plugin.
All solutions that I've seen requires using a IWorkspace. But, I want to use the CDT parser on single files outside eclipse. Is there any way to do that?
It depends what you mean by "without Eclipse".
CDT's code is built on top of the Eclipse Platform, so you're going to need to be running an application that includes the Eclipse Platform. However, there's no reason that application can't be a command-line application. These are called "headless" applications in the Eclipse community, and you can find many tutorials for making one (here's one).
Requiring an IWorkspace shouldn't be a problem. You can e.g. create a workspace and a project in a temporary folder, and copy the code to be analyzed there.
If, for some reason, you really want to use just CDT's parser in an application that doesn't include the Eclipse Platform, you can probably copy the parser code from CDT, and replace any dependencies it has on the Eclipse Platform with your own implementations. However, this is likely to be a more labour-intensive approach, and I wouldn't recommend it.