How to get error message from glz::err_ctx?

[Please-just-dont]

Hi, when I get an error, how am I supposed to a human readable error message? I can see through the debugger that the ec is 'unknown_key'. How can I get this as a string. Also, is that all the info that's provided? Just 'unknown_key', does it show the name of the actual key?

Thank you.

[stephenberry]

Call the function glz::format_error(ec, buffer). This will generate a std::string showing where the error occurred along with the serialized error code.

If you have a recent version of Glaze then the specific missing key will be included in the formatted error.

[Please-just-dont]

@stephenberry Thank you. I've got the newest one from Github, and it gives me "index 13: unknown_key". I was reading in json, does this mean an unknown key in the json or the struct it's deserialising into? Is it possible to give the name of the key?

[stephenberry]

You should see the first missing key for the struct you are reading into. Your message looks like you aren't feeding the buffer to glz::format_error.

[Please-just-dont]

@Please-just-dont OK, I tried doing it with reflect_cpp, and I got:

1. Field named 'orbitalPerdiod' not found.
2. Field named 'numGridTilesX' not found.
3. Field named 'numGridTilesY' not found.

I think I'll keep reflect-cpp around as it might come in handy.

Thank you.

[stephenberry]

Glaze is multiple times faster than reflect-cpp for many different operations, including error handling. At some point we might provide all missing keys in the output, but the design stands as it is to avoid dynamic allocations. Glaze provides only the first missing key in the sequence of the struct's keys.

If you want to handle all unknown keys you and have them all redirected to a dynamic map: See Unknown Keys documentation for more details.

[Please-just-dont]

@Please-just-dont Just letting you know the differences in case you wanted to know. In Glaze if you have a field in your struct that's not in the JSON it's just ignored. In reflect-cpp if it's in your struct but not in the json it gives as error UNLESS you wrap the field in an optional.

It seems that in both Glaze and reflect-cpp if there's a field in the json and not in your struct that's an outright error.

[stephenberry]

Right. By default Glaze errors on unknown keys, but this can be turned off with the option: error_on_unknown_keys. This is on by default as it gives the highest performance.

The error_on_missing_keys option in Glaze will error if keys are missing. Skipping is the default behavior, as sometimes only some of the fields are of interest and is higher performance. Using error_on_missing_keys gives behavior like reflect-cpp.

If you want to handle all unknown keys, Glaze provides the ability to map unknown keys into a dynamic map. You can have all unknown keys for a struct be written into a map. See Unknown Keys documentation for more details.

[Please-just-dont]

@stephenberry Hmm, so if you want to provide options you have to use read instead of read_json, right? And if you do there' no longer the overload that returns the struct in glz::expected but only the overload where you pass in the buffer, right? There's no difference between these methods?

[stephenberry]

You're correct. If you'd like, we could add a version for read with options that also allocates the value. The version that returns expected is just a simple wrapper around the core API that takes in the buffer so that it can be reused for better performance.

[Please-just-dont]

@stephenberry "If you'd like, we could add a version for read with options that also allocates the value" - no that's OK, I can just pass the buffer in. I'm keeping both Glaze and reflect-cpp wrapped up so I can use both of them. Just to let you know, to get the error you do:

glz::format_err(glz::err_ctx);

and it returns an std::string with "unknown_key". Then there's another overload thats:

glz::format_err(glz::err_ctx, const auto& buffer);

And if you pass an std::string to the const auto& buffer it returns:

"index 13: unknown_key"

So a bit more information, but the index 13 doesn't correspond to anything.

Also, the string that I pass into the buffer as second argument is always empty, not sure what that's supposed to be for.

Thank you for everything.

[stephenberry]

Oh, I see an issue to be fixed with Glaze here. Your input is probably 12 characters and index 13 is past the length of your buffer so it can't give more context. If the error occurs within the buffer then it can provide more information, which includes the missing key. I'll fix this.

[stephenberry]

I added an issue here for this: #1791

[stephenberry]

@Please-just-dont, a fix has been merged into main that will actually include the missing key in the formatted error message for top level objects like your use case.