Actually, I still have a very poor understanding of the c++ language. Many thanks to those who will help me.
I’m trying to use my library named “mylib.h” in namespace blink but the program gives me an undefined symbol error, while when I use it in namespace language I don’t get any error. I don’t know how to define the symbol.

lld-link: error: undefined symbol: public: static bool __cdecl MyDataManager::MyClientR(class std::__Cr::vector<double, class std::__Cr::allocator> &)

referenced by …..third_partyblinkrenderercoredomelement.cc:2435.

[[enter image description here](https://i.sstatic.net/rZfeH5kZ.jpg)](https://i.sstatic.net/rEhMWMSk.jpg)

I spent more than two days with it. Tried adding the library to the BUILD.gn file, but still can’t fix it. All your answers are valuable to me, don’t hesitate. Thank.