CODEWITHSUNDEEP
c++qtlinkerqt-creator
Tom
Tom

Reputation: 4087

QT creator doens't linking

I have a project with 2 subproject (Sub1 and Sub2):

ESI
|
|__Sub1
|
|__Sub2

In a implementation file (.cpp) of a class in the Sub2 (demo1.cpp) project i've the needs of include a class of the Sub1 project. So in the demo1.cpp i've declared:

#include "../sub1/controller.h"

Why the linker doesn't find the constructor of the controller? (says undefined reference)

Upvotes: 2

Views: 96

Answers (1)

Tim Meyer
Tim Meyer

Reputation: 12600

Your #include tells the Compiler where it can find the definition of your controller class (i.e. the content of your controller.h file).

In order to link towards the implementation of your controller class, the linker requires a library which contains the already compiled implementation. - The Sub2 project does not compile the contents of Sub1 again, unless you include the .cpp files of Sub1 in your Sub2 project which would be bad practice and could lead to further problems, however.

Assuming Sub1 is a library which will be generated as sub1.lib:

You need to add the following lines to your .pro file of your Sub2 project:

LIBS += -L../Sub1 \
        -lsub1

This tells the linker that there is a "../Sub1" directory which contains libraries and that there is a library called "sub1.lib". The advantage of using the -L and -l syntax is that this works on all platforms (Windows, Linux, Mac, etc).

If both Sub1 and Sub2 are executables (i.e. the projects produce a .exe) file, you need to extract the common content into a separate project Sub3 which has TEMPLATE = lib instead of TEMPLATE = app in its .pro file.

Upvotes: 2

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