Step-by-step guide
For the moment there is no simple way of knowing what the type of a key value is. However, the library provides a function that can be used to find out what the native type of a key value is.
The function, available only in the C API, is called 'grib_get_native_type'. Possible key value types are the following: undefined, long, double, string, bytes, section, label or missing.