From a static function, you can call only static function or use static variable. The linking is done at run time. So, though your compilation will be fine but at run time it will fail when call is made. Try making your function non static if you want to make that call.
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The only way to call a non-static method from a static method is to have an instance of the class containing the non-static method. By definition, a non-static method is one that is called ON an instance of some class, whereas a static method belongs to the class itself.
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solved can I call instance method of a static member from within static context?