QT error: invalid use of 'this' outside of a non-static member function code example

Example: QT error: invalid use of 'this' outside of a non-static member function

/**
 * your function may not be part of an object
 * didn't you forget how to declare a member function?
 */
returnType className::function_name(type arg1, type arg2, type argN){
	//any code
}