Numbering format for listings (lstlisting)

Question

I'm writing a document with a lot of listings ini it. I need to index the listing with the following format: "Listing a.b" with: a the chapter (arabic) and b the order of occurence in that chapter (arabic).

I have tried

\AtBeginDocument{\renewcommand\thelstlisting{\arabic{chapter}.\arabic{section}}}

But this creates a the chapter (arabic) and b the section of that chapter (arabic).

I have done similar thing for tables succesfully (in cls file), using:

\AtBeginDocument{ \renewcommand \thetable{\ifnum \c@chapter>\z@ \@arabic\c@chapter.\fi \@arabic\c@table} }

Answer 1

Found it! Apparently it's as simple as:

\AtBeginDocument{%
    \renewcommand\thelstlisting{\arabic{chapter}.\arabic{lstlisting}}%
}