On first printf the output is Button , while for second it is December which is as expected , the problem is that there is not any change in gui label of button of my gtk application . It througout shows button rather than december
Ok, I found the bug: you are calling twice to builder_init(), so the first time you are setting the label in an object, and then you are creating a new one which is the one that finally is shown in the window.
After reading this I saperated my single glade file in two files one with main top level window i.e. ApplicationWindow and another with inner widgets like Box and so on .