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api/basic_json/parse.md

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+# <small>nlohmann::basic_json::</small>parse
+
+```cpp
+// (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,
+                        const bool ignore_trailing_commas = false);
+
+// (2)
+template<typename IteratorType>
+static basic_json parse(IteratorType first, IteratorType last,
+                        const parser_callback_t cb = nullptr,
+                        const bool allow_exceptions = true,
+                        const bool ignore_comments = false,
+                        const bool ignore_trailing_commas = false);
+```
+
+1. Deserialize from a compatible input.
+2. Deserialize 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.
+
+## Template parameters
+
+`InputType`
+:   A compatible input, for instance:
+    
+    - an `std::istream` object
+    - a `FILE` pointer (throws if null)
+    - a C-style array of characters
+    - a pointer to a null-terminated string of single byte characters (throws if null)
+    - 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.
+
+`cb` (in)
+:   a parser callback function of type [`parser_callback_t`](parser_callback_t.md) 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)
+
+`ignore_trailing_commas` (in)
+:   whether trailing commas in arrays or objects 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 the start of a character range
+
+`last` (in)
+:   iterator to the end of a 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`. The latter can be checked with [`is_discarded`](is_discarded.md).
+
+## Exception safety
+
+Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
+
+## Exceptions
+
+- Throws [`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token, or
+  empty input like a null `FILE*` or `char*` pointer.
+
+## 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
+
+A UTF-8 byte order mark is silently ignored.
+
+Invalid Unicode escapes and unpaired surrogates in the input are reported as
+[`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) with a detailed message.
+
+## Examples
+
+??? example "Parsing from a character array"
+
+    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 "Parsing from a string"
+
+    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 "Parsing from an input stream"
+
+    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 "Parsing from a contiguous container"
+
+    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"
+    ```
+
+??? example "Parsing from a non-null-terminated string"
+
+    The example below demonstrates the `parse()` function reading from a string that is not null-terminated.
+
+    ```cpp
+    --8<-- "examples/parse__pointers.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/parse__pointers.output"
+    ```
+
+??? example "Parsing from an iterator pair"
+
+    The example below demonstrates the `parse()` function reading from an iterator pair.
+
+    ```cpp
+    --8<-- "examples/parse__iterator_pair.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/parse__iterator_pair.output"
+    ```
+
+??? example "Effect of `allow_exceptions` parameter"
+
+    The example below demonstrates the effect of the `allow_exceptions` parameter in the `parse()` function.
+
+    ```cpp
+    --8<-- "examples/parse__allow_exceptions.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/parse__allow_exceptions.output"
+    ```
+
+??? example "Effect of `ignore_comments` parameter"
+
+    The example below demonstrates the effect of the `ignore_comments` parameter in the `parse()` function.
+
+    ```cpp
+    --8<-- "examples/comments.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/comments.output"
+    ```
+
+??? example "Effect of `ignore_trailing_commas` parameter"
+
+    The example below demonstrates the effect of the `ignore_trailing_commas` parameter in the `parse()` function.
+
+    ```cpp
+    --8<-- "examples/trailing_commas.cpp"
+    ```
+
+    Output:
+
+    ```
+    --8<-- "examples/trailing_commas.output"
+    ```
+
+## See also
+
+- [accept](accept.md) - check if the input is valid JSON
+- [sax_parse](sax_parse.md) - parse input using the SAX interface
+- [operator>>](../operator_gtgt.md) - deserialize from stream
+
+## 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.
+- Changed [runtime assertion](../../features/assertions.md) in case of `FILE*` null pointers to exception in version 3.12.0.
+- Added `ignore_trailing_commas` in version 3.12.x.
+
+!!! warning "Deprecation"
+
+    Overload (2) replaces calls to `parse` 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 parse({ptr, ptr+len}, ...);` with `#!cpp parse(ptr, ptr+len, ...);`.
+
+    You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated
+    function.