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api/basic_json_document/accept/index.md

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+# nlohmann::basic_json_document::accept
+
+```
+template<typename InputType>
+static bool accept(InputType&& input,
+                   const bool ignore_comments = false,
+                   const bool ignore_trailing_commas = false);
+```
+
+Checks whether the input is valid JSON, accepting and rejecting exactly what [`BasicJsonType::accept()`](https://json.nlohmann.me/api/basic_json/accept/index.md) does, with the same options. Unlike [`parse()`](https://json.nlohmann.me/api/basic_json_document/parse/index.md), this function never throws an exception for invalid input, and the returned `bool` is the only result -- no document is returned.
+
+The result is the same as that of `BasicJsonType::accept()` by design; the difference is how the check is made. This function runs the document's index builder (and discards the index), while `BasicJsonType::accept()` runs the SAX parser with a handler that ignores every event. Use this one if you go on to parse the same input with [`parse()`](https://json.nlohmann.me/api/basic_json_document/parse/index.md) anyway, so that both use the same code; either is fine for a plain yes/no answer.
+
+## Template parameters
+
+`InputType` : A compatible input; see [`parse`](https://json.nlohmann.me/api/basic_json_document/parse/#template-parameters).
+
+## Parameters
+
+`input` (in) : Input to check.
+
+`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)
+
+## Return value
+
+Whether the input is valid JSON.
+
+## Exception safety
+
+Strong guarantee: this function itself never throws for an invalid input; it can only throw what allocating the input's own copy (for inputs that are always read into a buffer) throws.
+
+## Complexity
+
+Linear in the length of the input.
+
+## Notes
+
+An integer argument that is not a `bool` where the flags are expected, such as `accept(ptr, len)`, does not compile; see [`parse`](https://json.nlohmann.me/api/basic_json_document/parse/#notes).
+
+## Examples
+
+Example
+
+```
+#include <iostream>
+#include <nlohmann/json.hpp>
+#include <nlohmann/json_view.hpp>
+
+using json_document = nlohmann::json_document;
+
+int main()
+{
+    std::cout << std::boolalpha;
+
+    // accept() behaves exactly like basic_json::accept(): the same inputs are
+    // accepted or rejected, with the same ignore_comments/ignore_trailing_commas
+    // options
+    std::cout << json_document::accept(R"({"a": 1})") << '\n';
+    std::cout << json_document::accept(R"({"a": 1,})") << '\n'; // trailing comma: rejected by default
+    std::cout << json_document::accept(R"({"a": 1,})", false, true) << '\n'; // ignore_trailing_commas
+
+    std::cout << (json_document::accept(R"({"a": 1})") == nlohmann::json::accept(R"({"a": 1})")) << '\n';
+}
+```
+
+Output:
+
+```
+true
+false
+true
+true
+```
+
+## See also
+
+- [parse](https://json.nlohmann.me/api/basic_json_document/parse/index.md) - deserialize from a compatible input
+- [`BasicJsonType::accept`](https://json.nlohmann.me/api/basic_json/accept/index.md) - the corresponding function of `basic_json`
+
+## Version history
+
+- Added in version 3.13.0 unreleased.