json/doc/mkdocs/docs/api/basic_json/parse.md

basic_json::parse

// (1)
template<typename InputType>
static basic_json parse(InputType&& i,
                        const parser_callback_t cb = nullptr,
                        const bool allow_exceptions = true,
                        const bool ignore_comments = false);

// (2)
static basic_json parse(iterator first, iterator last,
                        const parser_callback_t cb = nullptr,
                        const bool allow_exceptions = true,
                        const bool ignore_comments = false);
static basic_json parse(const_iterator first, const_iterator last,
                        const parser_callback_t cb = nullptr,
                        const bool allow_exceptions = true,
                        const bool ignore_comments = false);

1. Deserialize from a compatible input.

2. Deserialize from a pair of character iterators

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

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
• an object obj for which begin(obj) and end(obj) produces a valid pair of iterators.

Parameters

i (in)

Input to parse from.

cb (in)

a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)

allow_exceptions (in)

whether to throw exceptions in case of a parse error (optional, #!cpp true by default)

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

Deserialized JSON value; in case of a parse error and allow_exceptions set to #!cpp false, the return value will be value_t::discarded.

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. The complexity can be higher if the parser callback function cb or reading from (1) the input i or (2) the iterator range [first, last] has a super-linear complexity.

Notes

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

Examples

??? example

The example below demonstrates the `parse()` function reading from an array.

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

Output:

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

??? example

The example below demonstrates the `parse()` function with and without callback function.

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

Output:

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

??? example

The example below demonstrates the `parse()` function with and without callback function.

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

Output:

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

??? example

The example below demonstrates the `parse()` function reading from a contiguous container.

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

Output:

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

Version history

• Added in version 1.0.0.
• Overload for contiguous containers (1) added in version 2.0.3.
• Ignoring comments via ignore_comments added in version 3.9.0.