I found a problem when compiling drogon: If you don’t link libjsoncpp.so, then all Json :: Values are "Unreferenced to...", as shown in the figure:

But if you connect libjsoncpp.so like:

That still has a few Json :: Value is unreferenced to, as shown in the figure:

.

After compiling,the item "Jsoncpp" has only four libs,and I’ve tried linking every one, but the ending is always like the above. So I’m wondering how I can solve this problem and why does it occur?