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85 lines
3.3 KiB
Markdown
85 lines
3.3 KiB
Markdown
# nlohmann::basic_json_document::accept
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```
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template<typename InputType>
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static bool accept(InputType&& input,
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const bool ignore_comments = false,
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const bool ignore_trailing_commas = false);
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```
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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.
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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.
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## Template parameters
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`InputType` : A compatible input; see [`parse`](https://json.nlohmann.me/api/basic_json_document/parse/#template-parameters).
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## Parameters
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`input` (in) : Input to check.
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`ignore_comments` (in) : whether comments should be ignored and treated like whitespace (`true`) or yield a parse error (`false`); (optional, `false` by default)
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`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)
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## Return value
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Whether the input is valid JSON.
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## Exception safety
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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.
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## Complexity
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Linear in the length of the input.
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## Notes
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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).
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## Examples
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Example
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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#include <nlohmann/json_view.hpp>
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using json_document = nlohmann::json_document;
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int main()
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{
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std::cout << std::boolalpha;
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// accept() behaves exactly like basic_json::accept(): the same inputs are
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// accepted or rejected, with the same ignore_comments/ignore_trailing_commas
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// options
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std::cout << json_document::accept(R"({"a": 1})") << '\n';
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std::cout << json_document::accept(R"({"a": 1,})") << '\n'; // trailing comma: rejected by default
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std::cout << json_document::accept(R"({"a": 1,})", false, true) << '\n'; // ignore_trailing_commas
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std::cout << (json_document::accept(R"({"a": 1})") == nlohmann::json::accept(R"({"a": 1})")) << '\n';
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}
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```
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Output:
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```
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true
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false
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true
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true
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```
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## See also
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- [parse](https://json.nlohmann.me/api/basic_json_document/parse/index.md) - deserialize from a compatible input
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- [`BasicJsonType::accept`](https://json.nlohmann.me/api/basic_json/accept/index.md) - the corresponding function of `basic_json`
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## Version history
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- Added in version 3.13.0 unreleased.
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