Linker error: undefined reference to `std::ctype<char>::_M_widen_init()

Answer 1

It looks like it's part of the standard library that's mismatched here. The two most likely answers I can think of:

• You didn't compile and link the entire project (including all libraries) with the same version of g++.
• The header/library paths you're using for the standard library mismatch, and you're getting the headers from one library version but the .so library from a different version.