Sets the double pointed to by value corresponding to the value of the
given field. Caller is responsible for making sure the field exists
and has the correct type.
TRUE if the value could be set correctly. If there was no field
with fieldname or the existing field did not contain a double, this
function returns FALSE.
Sets the double pointed to by value corresponding to the value of the given field. Caller is responsible for making sure the field exists and has the correct type.