Niels Lohmann
63c10a51fc
* Review and extend the documentation, and check it in CI A review of all documentation pages found factual errors, dead links, missing cross-references, and gaps in examples. This fixes them and adds checks so the same problems are caught automatically. Fixes: - wrong signatures and version histories (operator!= C++20 member, binary() subtype type, get<PointerType>(), JSON_NO_THREAD_LOCAL, ...) - stale descriptions (number parsing since #5283, UBJSON table, SAX example that no longer compiled, tsl::ordered_map advice) - dead internal and external links; repology.org badges (the domain is suspended) replaced by badges that query the registries directly - deprecation notes link the migration guide; the guide itself fixed Additions: - "See also" sections, cross-references, 25 runnable examples, 12 Mermaid diagrams, new API pages for json_pointer::operator<=> and byte_container_with_subtype::operator==/!= - landing page, guides for untrusted input and performance - "unreleased" badge after versions newer than the latest release Checks: - strict documentation build (broken links/anchors fail it); CI and the publish workflow fetch the full history the build needs - weekly external link check, Mermaid syntax check in CI - check_structure.py: example titles, heading levels, alt texts, header links, docset index coverage; its unused-example check works again - all examples produce the same output on every platform Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Keep the customer links that could not be fixed A dead link on the customers page is still the evidence of where the use of the library was documented. Keep the original URLs of the entries without a working replacement (Marne, Cisco Webex Desk Camera, Philips Hue, CyberArk) and exclude exactly these URLs from the link check. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct the duplicate-key recipe's claim about SAX positions The SAX interface's key() receives no position either; only parse_error() does. Also note that the recipe does not report the path to the repeated key (see discussion #5085). Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Say the library is available as a single header and mention json_fwd.hpp Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct documentation errors found while hunting for bugs - patch/patch_inplace: list the JSON pointer errors parse_error.106-109 and out_of_range.402/404, and quote the actual parse_error.105 message. - unflatten: list parse_error.106/107/108 and out_of_range.404. - to_bson: list out_of_range.415 (binary subtype above 255) and note that 412 and 415 are new in 3.13.0. - to_string: state that string_t must be convertible to std::string, also in the StringType requirements table. - JSON Lines: a `while (input >> j)` loop also throws after the last value for concatenated JSON values; show a loop that works for both. - BON8: a string gets 0xFF only if nothing follows it in the message; a string at the end of an array or object is ended by 0xFE. - custom_string_type.hpp: add operator+=(char), which the "Always required" list asks for (json_pointer::to_string, flatten, unflatten, and diff did not compile), and an ADL int_to_string for diff and items. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Cache the release headers with functools.lru_cache Codacy (Pylint) flagged the mutable default argument that header() used as its cache. functools.lru_cache keeps the same memoization without it. The script's output is unchanged. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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Parsing and Exceptions
When the input is not valid JSON, an exception of type parse_error is thrown.
This exception contains the position in the input where the error occurred, together with a diagnostic message and the
last read input token. The exceptions page contains a
list of examples for parse error exceptions. In case you process untrusted
input, always enclose your code with a #!cpp try/#!cpp catch block, like
json j;
try
{
j = json::parse(my_input);
}
catch (json::parse_error& ex)
{
std::cerr << "parse error at byte " << ex.byte << std::endl;
}
In case exceptions are undesired or not supported by the environment, there are different ways to proceed:
Switch off exceptions
The parse() function accepts a #!cpp bool parameter allow_exceptions which
controls whether an exception is thrown when a parse error occurs (#!cpp true, default) or whether a discarded value
should be returned (#!cpp false).
json j = json::parse(my_input, nullptr, false);
if (j.is_discarded())
{
std::cerr << "parse error" << std::endl;
}
Note there is no diagnostic information available in this scenario.
Use accept() function
Alternatively, function accept() can be used which does not return a json value,
but a #!cpp bool indicating whether the input is valid JSON.
if (!json::accept(my_input))
{
std::cerr << "parse error" << std::endl;
}
Again, there is no diagnostic information available.
User-defined SAX interface
Finally, you can implement the SAX interface and decide what should happen in case of a parse error.
This function has the following interface:
bool parse_error(std::size_t position,
const std::string& last_token,
const json::exception& ex);
The return value indicates whether the parsing should continue, so the function should usually return #!cpp false.
??? example "Example: report parse errors without exceptions"
The example derives from the library's DOM parser and overrides `parse_error` to print the error instead of
throwing. Note the DOM parser is an implementation detail (`nlohmann::detail`) and may change between releases;
see [Do not use the `detail` namespace](../../integration/migration_guide.md#do-not-use-the-detail-namespace).
```cpp
--8<-- "examples/sax_no_exception.cpp"
```
Output:
```
--8<-- "examples/sax_no_exception.output"
```