How can I find out the value of $(ProjectDir)?

Do a pre/post build step.

Example:

echo $(ProjectDir)

To find out what it is right now (rather than at build time, where it may be different depending on what is going on):

• right click on your project in the Solution Explorer, select Properties
• select the Build Events tab
• click the Edit pre-build or Edit post-build button, either is fine
• in the window that pops up, click the Macros button
• scroll down the list till you find ProjectDir, in the next pane is its actual value