C++ Linking problem

All of the errors are indicative of wrong C runtime settings with your builds. Make sure that all of your object files, libraries, etc are compiled with the same runtime setting, that is:

• Multithreaded (/MT)
• Multithreaded DLL (/MD)
• Multithreaded Debug (/MTd)
• Multithreaded Debug DLL (/MDd)

If this setting isn't the same for all the projects, you've violated the one definition rule (because each C runtime defines things differently) which would result in the behavior you're seeing.

My guess is that the JSONCPP library is being built assuming the static version of the standard library (/MT), while your code is using the Visual Studio default, which is the dynamically linked version (/MD).

You can change this setting from within Visual Studio by selecting the project properties for your project, going to C/C++ -> Code Generation, and changing the Runtime dropdown box.

MSDN has good docs on this.

In short, /MDd links the necessary parts of a debug build of the C & C++ standard libraries into your DLL. /MD is similar but uses a NDEBUG version of the standard libraries. If you try to link code that combines debug and release standard libraries, you'll get symbol clashes as both libraries will provide the same set of functions.