Linker errors LNK2001 and LNK2019

Question

I am compiling my Qt project using compiler MSVC2008, and I am getting linker errors like-

_class_name.obj_:error LNK2001: unresolved external symbol "public: static struct QMetaObject...."... referenced in a function "_function_name_"

_class_name.obj_:error LNK2019: unresolved external symbol "public: static struct QMetaObject..." ... referenced in a function "_function_name_"

I have few basic queries-

1. what does it mean by errors LNK2001 and LNK2019?

2. Why these error occurs?

3. How to resolve these?

NOTE: I am using QtCreater so build system uses qmake and compiler used is MSVC2008.

Answer 1

1. In a nutshell, you used a function which is declared but not defined.

2. It should be caused by your classes using Qt functionality (like signal-slots) but incorrectly.

3. Here's possibilities I can think of:

   3-a. Double check you've written "Q_OBJECT" at the beginning of your class that use Qt functionality.

   3-b. You call "moc" property, i.e. check if your Qt Visual Studio plugin is installed and enabled.

Answer 2

You've included the wrong/too little files or forgot to add .lib files to the Linker in msvc.

Check under linker's Additional Dependencies property for: QtCore5.lib - for Qt5 Release QtCore5d.lib - for Qt5 Debug

QMetaObject is included in one of those, but they might not be the only dependencies in your project.