Returns the values associated with key under group_name as
doubles.
If key cannot be found then NULL is returned and error is set to
G_KEY_FILE_ERROR_KEY_NOT_FOUND. Likewise, if the values associated
with key cannot be interpreted as doubles then NULL is returned
and error is set to G_KEY_FILE_ERROR_INVALID_VALUE.
Since 2.12
Returns the values associated with key under group_name as doubles. If key cannot be found then NULL is returned and error is set to G_KEY_FILE_ERROR_KEY_NOT_FOUND. Likewise, if the values associated with key cannot be interpreted as doubles then NULL is returned and error is set to G_KEY_FILE_ERROR_INVALID_VALUE. Since 2.12