Object of class charts could not be converted to string

I have written a class for which the constructor function has 3 arguments. In some function of the class I have to query from db like this $profit_row->operating_profit.

now instead of writing operating_profit, I want to pass it as a variable to the constructor of the class. So my whole variable becomes $profit_row->$this->num where $this->num is initialized in the constructor.

When I do this I get the following error. How to go about this. Object of class charts could not be converted to 开发者_开发知识库string

Maybe this is what you are looking for?

$profit_row->{$this->num}

$profit_row->{$this->num}

you have a precedence problem.