wxWidgets provides a set of utility methods to converts wxString to various integer types such as ToLong(). While the documentation for those functions remained roughly the same between wxWidgets 2.8 and 3.0 the implementation did change. In wxWidgets 2.8, if the string was empty, using any of the number converstion functions would result in the value 0. But, in wxWidgets 3.0 it’s different as can be learned from the following comment in wxstring.cpp:
// notice that we return false without modifying the output parameter at all if
// nothing could be parsed but we do modify it and return false then if we did
// parse something successfully but not the entire string
This means that if you relied on ToLong() to store 0 to the pointer to long when given empty string, in wxWidgets 3.0 you will get uninitialized value there.
I also noticed when comparing the code of wxString in 2.8 and 3.0, that they implemented the integer conversion functions using C macros, while in 2.8 they used templates. I wonder why it was changed, as it looks more like a regression to me.