Undefined reference to symbol in static lib

[Besajia]

There are

lib1.a

lib1 has class Lib1Class

lib2.a

lib2.a depends on lib1.a and use Lib1Class

app

app depends of lib2.a and app does not user lib1Class

app.pro

TARGET = app

LIBS += -Llibs_path -llib1 -llib2

INCLUDEPATH +=  headers_path

So when I build app I get undefined reference Lib1Class when linking stage.

Miracle occurs if I start using Lib1Class in app. i.e. in main.cpp create instance of class Lib1Class. Everything is linked and works.

I tried to use PRE_TARGETDEPS = $${libs_build_dir}/lib1.a and it does not help.

Help me to build app please.

[Christian Ehrlicher]

You need to reverse your link order when I'm correct

LIBS += -Llibs_path -llib2 -llib1

See also google for 'c++ link order static', e.g. https://eli.thegreenplace.net/2013/07/09/library-order-in-static-linking

[David_001]

lib2.so depends on lib1.so

=> therefore you have to say that inside your pro

lib2.depends = lib1

maybe as well
app.depends = lib1