Using returnvalue from function in dataTables

Hi.
Trying to use a returnvalue from a function, but for some reason, it doesn't seem to return anything, and I'm a little confused as to why.
Function:

Code (text):

function getTableLength() {

   $.post(‘get_post.php’,{ tablelength:’yes’},function(data) {

     data = $.parseJSON(data);

     return data.content;

   })

}

and trying to use it here:

Code (text):

    $("#showallusers_table,#meetings_table").dataTable( {

       ’iDisplayLength’   : getTableLength()

    });

But it doesn't…
Using returnvalue from function in dataTables

See original post by PoPSiCLe