c++ - static variable initialisation code never gets called

Question

I've got an application that's using a static library I made. One .cpp file in the library has a static variable declaration, whose ctor calls a function on a singleton that does something- e.g. adds a string.

Now when I use that library from the application, my singleton doesn't seem to contain any traces of the string that was supposed to be added.

I'm definitely missing something but I don't know what..

Answer 1

If you have an object in a static library that is not EXPLICITLY used in the application. Then the linker will not pull that object from the lib into the application.

There is a big difference between static and dynamic libraries.

Dynamic Library:
At compile time nothing is pulled from the dynamic library. Extra code is added to explicitly load and resolve the symbols at run-time. At run time the whole library is loaded and thus object initializers are called (though when is implementation detail).

Static libraries are handled very differently:
When you link against a static library it pulls all the items that are not defined in application that are defined in the library into the application. This is repeated until there are no more dependencies that the library can resolve. The side effect of this is that objects/functions not explicitly used are not pulled form the library (thus global variables that are not directly accessed will not be pulled).