69 lines
2.3 KiB
Markdown
69 lines
2.3 KiB
Markdown
# nlohmann::basic_json_view::cbegin
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```
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iterator cbegin() const noexcept;
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```
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Returns an iterator to the first element, in [document order](https://json.nlohmann.me/api/basic_json_view/begin/index.md). Equivalent to [`begin()`](https://json.nlohmann.me/api/basic_json_view/begin/index.md): a view is always read-only, so `const_iterator` and `iterator` are the same type, and `cbegin()` exists only so that generic code that expects a `cbegin()`/`cend()` pair works with a view too.
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## Return value
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Iterator to the first element; identical to what [`begin()`](https://json.nlohmann.me/api/basic_json_view/begin/index.md) returns.
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## Exception safety
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No-throw guarantee: this function never throws exceptions.
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## Complexity
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Constant.
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## Examples
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Example
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The example below sums many measurements with `std::accumulate`, using `cbegin()`/[`cend()`](https://json.nlohmann.me/api/basic_json_view/cend/index.md) as the range -- the same way it would for any standard container -- without ever materializing the whole array into a `BasicJsonType` value.
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```
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#include <iostream>
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#include <numeric>
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#include <nlohmann/json_view.hpp>
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using json_document = nlohmann::json_document;
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using json_view = nlohmann::json_view;
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int main()
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{
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// sum many measurements with std::accumulate; cbegin()/cend() (identical
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// to begin()/end() here -- the view is always read-only) let the view be
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// used with standard algorithms without ever materializing the whole
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// array into a nlohmann::json value
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json_document measurements = json_document::parse("[3, 1, 4, 1, 5, 9, 2, 6]");
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const auto values = measurements.root();
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const int sum = std::accumulate(values.cbegin(), values.cend(), 0,
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[](int total, const json_view & v)
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{
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return total + v.materialize().get<int>();
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});
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std::cout << sum << '\n';
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}
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```
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Output:
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```
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31
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```
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## See also
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- [begin](https://json.nlohmann.me/api/basic_json_view/begin/index.md) - returns an iterator to the first element
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- [cend](https://json.nlohmann.me/api/basic_json_view/cend/index.md) - returns a const iterator to one past the last element
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- [`BasicJsonType::cbegin`](https://json.nlohmann.me/api/basic_json/cbegin/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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