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Niels Lohmann 146e5e0bc7 Merge iterator+sentinel overloads and fix ambiguity/CI issues

Address PR review feedback and CI failures:

- Merge the separate same-type and sentinel-type iterator overloads of
  parse(), accept(), sax_parse(), and the five from_* binary deserializers
  into a single overload with SentinelType defaulted to IteratorType,
  as suggested in review. Applied the same simplification to the
  detail::input_adapter() free functions.
- Fix a latent ambiguity: some compilers (e.g. GCC 4.8) unreliably SFINAE
  the operator!= detection for std::nullptr_t against container/string
  types, making calls like parse(s, nullptr, ...) ambiguous with the
  compatible-input overload. can_compare_ne now explicitly excludes
  std::nullptr_t as a SentinelType.
- Use a named enable_if_t template parameter instead of an unnamed
  function parameter for the SFINAE guard, fixing a clang-tidy
  hicpp-named-parameter/readability-named-parameter failure.
- Update parse.md, accept.md, sax_parse.md, and the five from_*.md pages
  to document the merged overload instead of separate (2)/(3) overloads,
  also fixing an over-160-char line that broke the documentation
  style_check CI job.
- Rework the BSON iterator+sentinel test to parse a BSON file already
  present in the test suite instead of writing/deleting a temp file.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

2026-07-10 23:15:17 +02:00

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nlohmann::basic_json::from_bson

// (1)
template<typename InputType>
static basic_json from_bson(InputType&& i,
                            const bool strict = true,
                            const bool allow_exceptions = true);
// (2)
template<typename IteratorType, typename SentinelType = IteratorType>
static basic_json from_bson(IteratorType first, SentinelType last,
                            const bool strict = true,
                            const bool allow_exceptions = true);

Deserializes a given input to a JSON value using the BSON (Binary JSON) serialization format.

Reads from a compatible input.
Reads from an iterator range, or an iterator and a sentinel of a different type (C++20 ranges support).

The exact mapping and its limitations are described on a dedicated page.

Template parameters

InputType

A compatible input, for instance:

an std::istream object
a FILE pointer
a C-style array of characters
a pointer to a null-terminated string of single byte characters
a container obj for which begin(obj) and end(obj) produce a valid pair of iterators (as found via ADL or member functions, with semantics compatible to std::begin and std::end)

IteratorType

a compatible iterator type

SentinelType

defaults to IteratorType; may be a different type comparable to IteratorType via operator!=, for instance a custom sentinel type for C++20 ranges

Parameters

i (in): an input in BSON format convertible to an input adapter
first (in): iterator to the start of the input
last (in): iterator to the end of the input, or a sentinel value that compares equal to the end iterator with operator!=
strict (in): whether to expect the input to be consumed until EOF (#!cpp true by default)
allow_exceptions (in): whether to throw exceptions in case of a parse error (optional, #!cpp true by default)

Return value

deserialized JSON value; in case of a parse error and allow_exceptions set to #!cpp false, the return value will be value_t::discarded. The latter can be checked with is_discarded.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

Exceptions

Throws parse_error.110 if the given input ends prematurely or the end of the input was not reached when strict was set to true
Throws parse_error.112 if a parse error occurs (e.g., an invalid string or byte array length)
Throws parse_error.114 if an unsupported BSON record type is encountered

Complexity

Linear in the size of the input.

Examples

??? example

The example shows the deserialization of a byte vector in BSON format to a JSON value.
 
```cpp
--8<-- "examples/from_bson.cpp"
```

Output:

```json
--8<-- "examples/from_bson.output"
```

Version history

Added in version 3.4.0.
Extended container support (1) to include types with lvalue-only ADL begin/end (matching std::begin/std::end semantics) in version 3.13.0.
Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.

!!! warning "Deprecation"

- Overload (2) replaces calls to `from_bson` with a pointer and a length as first two parameters, which has been
  deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
  `#!cpp from_bson(ptr, len, ...);` with `#!cpp from_bson(ptr, ptr+len, ...);`.
- Overload (2) replaces calls to `from_bson` with a pair of iterators as their first parameter, which has been
  deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
  `#!cpp from_bson({ptr, ptr+len}, ...);` with `#!cpp from_bson(ptr, ptr+len, ...);`.

You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
function.

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