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api/basic_json/accept/index.md

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+# nlohmann::basic_json::accept
+
+```
+// (1)
+template<typename InputType>
+static bool accept(InputType&& i,
+                   const bool ignore_comments = false,
+                   const bool ignore_trailing_commas = false);
+
+// (2)
+template<typename IteratorType>
+static bool accept(IteratorType first, IteratorType last,
+                   const bool ignore_comments = false,
+                   const bool ignore_trailing_commas = false);
+```
+
+Checks whether the input is valid JSON.
+
+1. Reads from a compatible input.
+
+1. Reads from a pair of character iterators
+
+   The value_type of the iterator must be an integral type with a size of 1, 2, or 4 bytes, which will be interpreted respectively as UTF-8, UTF-16, and UTF-32.
+
+Unlike the [`parse()`](https://json.nlohmann.me/api/basic_json/parse/index.md) 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 (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.
+
+`ignore_comments` (in) : whether comments should be ignored and treated like whitespace (`true`) or yield a parse error (`false`); (optional, `false` by default)
+
+`ignore_trailing_commas` (in) : whether trailing commas in arrays or objects should be ignored and treated like whitespace (`true`) or yield a parse error (`false`); (optional, `false` by default)
+
+`first` (in) : iterator to the start of the character range
+
+`last` (in) : iterator to the end of the 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.
+
+## Exceptions
+
+Throws [`parse_error.101`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error101) in case of an 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.
+
+## Notes
+
+A UTF-8 byte order mark is silently ignored.
+
+## Examples
+
+Example
+
+The example below demonstrates the `accept()` function reading from a string.
+
+```
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // a valid JSON text
+    auto valid_text = R"(
+    {
+        "numbers": [1, 2, 3]
+    }
+    )";
+
+    // an invalid JSON text
+    auto invalid_text = R"(
+    {
+        "strings": ["extra", "comma", ]
+    }
+    )";
+
+    std::cout << std::boolalpha
+              << json::accept(valid_text) << ' '
+              << json::accept(invalid_text) << '\n';
+}
+```
+
+Output:
+
+```
+true false
+```
+
+## See also
+
+- [parse](https://json.nlohmann.me/api/basic_json/parse/index.md) - deserialize from a compatible input
+- [sax_parse](https://json.nlohmann.me/api/basic_json/sax_parse/index.md) - parse input using the SAX interface
+- [operator>>](https://json.nlohmann.me/api/operator_gtgt/index.md) - deserialize from stream
+
+## Version history
+
+- Added in version 3.0.0.
+- Ignoring comments via `ignore_comments` added in version 3.9.0.
+- Changed [runtime assertion](https://json.nlohmann.me/features/assertions/index.md) in case of `FILE*` null pointers to exception in version 3.12.0.
+- Added `ignore_trailing_commas` in version 3.12.x.
+
+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 `accept({ptr, ptr+len}, ...);` with `accept(ptr, ptr+len, ...);`.
+
+You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated function.