So there is no place in memory where b actually resides (the reference is undefined). To deal with this, you have to manually declare it in a cpp file, with the syntax int A::b; . This way you are reserving some space for that variable
undefined reference to `log' · Issue #110 · energia The math.h function 'log' doesn't seem to work in Energia, is this a known problem or is it just not supported by Energia? I created an log calculation but when i compiled i received an error: undefined reference to `log' collect2: ld re undefined reference to 'function' Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted! 1. The problem statement, all variables and given/known data: i know when undefined reference shows up the program is saying it is not link to that function but the problem undefined reference to `isDigit' - C Board
You're declaring all these variable as extern, but they don't seem to actually exist anywhere.When you say extern std::string nomEnnemi;, for example, you're not actually declaring a variable, but simply promising the compiler that it exists in another file.
Mar 06, 2011 "undefined reference to" a function i
c++ - undefined reference to template function - Stack
undefined reference to function - C++ Forum Sep 07, 2008 undefined reference to function? - C++ Forum Aug 07, 2015