lenn/json

mirror of https://github.com/nlohmann/json.git synced 2025-11-24 11:54:34 +08:00

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Florian Albrechtskirchinger e3095f636f Add operator<<(json_pointer) (#3601 )

* Add operator<< for json_pointer

* Deprecate json_pointer::operator string_t()

* Update documentation

* Move operator<<(basic_json) example

* Add example

* Add mkdocs-redirects

* Move operator<< and operator>> doc pages out of basic_json/

* Rename JSON pointer operator_string to operator_string_t

* Add unit test

2022-07-28 22:12:23 +02:00

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nlohmann::basic_json::accept

// (1)
template<typename InputType>
static bool accept(InputType&& i,
                   const bool ignore_comments = false);

// (2)
template<typename IteratorType>
static bool accept(IteratorType first, IteratorType last,
                   const bool ignore_comments = false);

Checks whether the input is valid JSON.

Reads from a compatible input.
Reads from a pair of character iterators

The value_type of the iterator must be an integral type with size of 1, 2 or 4 bytes, which will be interpreted respectively as UTF-8, UTF-16 and UTF-32.

Unlike the parse function, this function neither throws an exception in case of invalid JSON input (i.e., a parse error) nor creates diagnostic information.

Template parameters

InputType

A compatible input, for instance:

an std::istream object
a FILE pointer (must not be null)
a C-style array of characters
a pointer to a null-terminated string of single byte characters
a std::string
an object obj for which begin(obj) and end(obj) produces a valid pair of iterators.

IteratorType

a compatible iterator type, for instance.

a pair of std::string::iterator or std::vector<std::uint8_t>::iterator
a pair of pointers such as ptr and ptr + len

Parameters

i (in): Input to parse from.
ignore_comments (in): whether comments should be ignored and treated like whitespace (#!cpp true) or yield a parse error (#!cpp false); (optional, #!cpp false by default)
first (in): iterator to start of character range
last (in): iterator to end of character range

Return value

Whether the input is valid JSON.

Exception safety

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

Complexity

Linear in the length of the input. The parser is a predictive LL(1) parser.

Notes

(1) A UTF-8 byte order mark is silently ignored.

!!! danger "Runtime assertion"

The precondition that a passed `#!cpp FILE` pointer must not be null is enforced with a
[runtime assertion](../../features/assertions.md).

Examples

??? example

The example below demonstrates the `accept()` function reading from a string.

```cpp
--8<-- "examples/accept__string.cpp"
```

Output:

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

Version history

Added in version 3.0.0.
Ignoring comments via ignore_comments added in version 3.9.0.

!!! warning "Deprecation"

Overload (2) replaces calls to `accept` 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 accept({ptr, ptr+len}, ...);` with `#!cpp accept(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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