If you see Runtime error R6025 - Pure Virtual Function Call message when running an app, then one of these fixes is sure to help you.

A fast, small C/C++ function call tracer for x86-64/Linux, supports clang & gcc, ftrace, threads, exceptions & shared libraries - yosefk/funtrace ...

Uncaught Error: Call to undefined function ImageCreate () In case this error appears (e.g. in /var/log/apache2/error.log once calling simple_qr.php), the GD library is not ready.