Re: JSON parser error handling

From: Kenneth Porter (shiva_at_[hidden])
Date: 2022-04-26 08:06:25

--On Monday, April 25, 2022 4:49 PM -0700 Vinnie Falco 
<vinnie.falco_at_[hidden]> wrote:

> If your exception is coming from the call to parse() and you want to
> know where in the string you are, then you need to change your code to
> create an instance of json::parser and call parser::write or
> parser::write_some to feed in the input. These functions return the
> number of characters consumed, which will be less than the amount
> passed in if an error occurs. In this case, the number of characters
> parsed successfully can be used to calculate an offset into the input
> buffer to determine where the syntax error happened.
>
> If your exception is coming from the call to value_to<>(), things are
> not so simple. The original JSON string is no longer available, and
> information about which json::value came from what part of the string
> is not stored (that would slow down the library and take up
> unnecessary memory).

Aha, I begin to understand the issues. Two different classes of error can 
occur. Catching a problem in the parse() call would catch JSON syntax 
errors. My JSON was correct as it had been machine-generated from an online 
XML translator. I was seeing semantic errors in turning a valid JSON 
structure into my custom C++ structure. So I somehow need to figure out 
where in the hierarchy the translation failed. Given that, I could output 
the JSON structure as text with an indicator where the structure wasn't 
what the translator expected.