forked from Research/WhisperCom
Dominik Meyer
cc002ebfbb
git-subtree-dir: libs/json git-subtree-split: f42a74b8f53cc308647123d49d33d1c8122e3f42
157 lines
4.2 KiB
Markdown
157 lines
4.2 KiB
Markdown
# basic_json::parse
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```cpp
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// (1)
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template<typename InputType>
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static basic_json parse(InputType&& i,
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const parser_callback_t cb = nullptr,
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const bool allow_exceptions = true,
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const bool ignore_comments = false);
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// (2)
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template<typename IteratorType>
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static basic_json parse(IteratorType first, IteratorType last,
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const parser_callback_t cb = nullptr,
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const bool allow_exceptions = true,
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const bool ignore_comments = false);
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```
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1. Deserialize from a compatible input.
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2. Deserialize from a pair of character iterators
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The value_type of the iterator must be a integral type with size of 1, 2 or 4 bytes, which will be interpreted
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respectively as UTF-8, UTF-16 and UTF-32.
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## Template parameters
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`InputType`
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: A compatible input, for instance:
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- an `std::istream` object
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- a `FILE` pointer
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- a C-style array of characters
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- a pointer to a null-terminated string of single byte characters
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- an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of iterators.
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`IteratorType`
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: a compatible iterator type
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## Parameters
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`i` (in)
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: Input to parse from.
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`cb` (in)
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: a parser callback function of type [`parser_callback_t`](parser_callback_t.md) which is used to control the
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deserialization by filtering unwanted values (optional)
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`allow_exceptions` (in)
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: whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
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`ignore_comments` (in)
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: whether comments should be ignored and treated like whitespace (`#!cpp true`) or yield a parse error
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(`#!cpp false`); (optional, `#!cpp false` by default)
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`first` (in)
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: iterator to start of character range
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`last` (in)
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: iterator to end of character range
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## Return value
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Deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
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`value_t::discarded`. The latter can be checked with [`is_discarded`](is_discarded.md).
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## Exception safety
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Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
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## Complexity
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Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser
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callback function `cb` or reading from (1) the input `i` or (2) the iterator range [`first`, `last`] has a
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super-linear complexity.
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## Notes
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(1) A UTF-8 byte order mark is silently ignored.
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## Examples
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??? example "Parsing from a charater array"
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The example below demonstrates the `parse()` function reading from an array.
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```cpp
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--8<-- "examples/parse__array__parser_callback_t.cpp"
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```
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Output:
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```json
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--8<-- "examples/parse__array__parser_callback_t.output"
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```
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??? example "Parsing from a string"
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The example below demonstrates the `parse()` function with and without callback function.
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```cpp
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--8<-- "examples/parse__string__parser_callback_t.cpp"
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```
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Output:
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```json
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--8<-- "examples/parse__string__parser_callback_t.output"
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```
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??? example "Parsing from an input stream"
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The example below demonstrates the `parse()` function with and without callback function.
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```cpp
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--8<-- "examples/parse__istream__parser_callback_t.cpp"
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```
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Output:
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```json
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--8<-- "examples/parse__istream__parser_callback_t.output"
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```
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??? example "Parsing from a contiguous container"
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The example below demonstrates the `parse()` function reading from a contiguous container.
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```cpp
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--8<-- "examples/parse__contiguouscontainer__parser_callback_t.cpp"
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```
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Output:
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```json
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--8<-- "examples/parse__contiguouscontainer__parser_callback_t.output"
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```
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??? example "Effect of `allow_exceptions` parameter"
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The example below demonstrates the effect of the `allow_exceptions` parameter in the ´parse()` function.
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```cpp
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--8<-- "examples/parse__allow_exceptions.cpp"
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```
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Output:
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```json
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--8<-- "examples/parse__allow_exceptions.output"
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```
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## Version history
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- Added in version 1.0.0.
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- Overload for contiguous containers (1) added in version 2.0.3.
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- Ignoring comments via `ignore_comments` added in version 3.9.0.
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