Visual Studio (C++) is automatically linking against an unwanted version of lib file

Question

I am trying to create a C++ project in Visual Studio 2013 that has CGAL and Boost (and a couple of other libraries) as dependencies. I preferably like to link to these libraries dynamically. Also, I'd like to link to the "Release" versions of these libraries for performance reasons (not the "Debug" versions).

Starting from an empty C++ project, I added the path to header files of the aforementioned libraries as shown in the image below:

Inside the linker options, I then added the directories that contain the DLL and lib files of the external libraries. (CGAL directory contains CGAL's compiled DLL files along with lib files).

At this point, I have not added a single "lib" file "Additional Dependencies" dialog:

Now something weird is going on and I cannot explain why. If I try to build the project as-is (under the "Debug" configuration), I get a LNK1104 error about the linker not being able to find CGAL-vc120-mt-gd-4.7.lib. I know that the error means I should add the lib file in "Additional Dependencies" dialog...

But wait... WHAT...?!!
How does Visual Studio know how to automatically link against this lib file?! Worse yet, how does it know it needs the "debug" version of the library? (With the gd suffix). Also, how does it know I compiled CGAL with VS2013!!?? At first, I though the project was inheriting properties from some preset property sheets somewhere in my system. But I am certain that's not the case as this behavior shows even with a project created from scratch.

My main question is, how would you force Visual Studio to link against the "Release" version of this library? (eg. CGAL-vc120-mt-4.7.lib)

Side question but related: Am I even linking against the DLL files? How can I be certain that I am in deed doing dynamic linking and not static linking?

Answer 1

This is probably happening due to the #pragma comment(lib) mechanism - eg see What does "#pragma comment" mean?

This is a way of the compiler emitting instructions for the linker so that it can decide between multiple versions of a library depending on the compiler version. In this case it means that it can automatically pick up the correct version of the library (debug vs release, vs2013 vs vs2015, MT vs MD, etc). When you added the explicit reference to the library in Additional Dependencies then it is now trying to look for two files.

So, to fix the problem, remove it from Additional Dependencies and let VS pick the right library. If you are getting the LNK1104 error then it suggests that either the link library path isn't set up correctly, or you don't have the CGAL library file it's looking for. You can increase the verbosity settings for the linker in the Project Options to get more detail about what's happening.