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api/basic_json_view/cbegin/index.md

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+# nlohmann::basic_json_view::cbegin
+
+```
+iterator cbegin() const noexcept;
+```
+
+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.
+
+## Return value
+
+Iterator to the first element; identical to what [`begin()`](https://json.nlohmann.me/api/basic_json_view/begin/index.md) returns.
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Constant.
+
+## Examples
+
+Example
+
+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.
+
+```
+#include <iostream>
+#include <numeric>
+#include <nlohmann/json_view.hpp>
+
+using json_document = nlohmann::json_document;
+using json_view = nlohmann::json_view;
+
+int main()
+{
+    // sum many measurements with std::accumulate; cbegin()/cend() (identical
+    // to begin()/end() here -- the view is always read-only) let the view be
+    // used with standard algorithms without ever materializing the whole
+    // array into a nlohmann::json value
+    json_document measurements = json_document::parse("[3, 1, 4, 1, 5, 9, 2, 6]");
+    const auto values = measurements.root();
+
+    const int sum = std::accumulate(values.cbegin(), values.cend(), 0,
+                                    [](int total, const json_view & v)
+    {
+        return total + v.materialize().get<int>();
+    });
+
+    std::cout << sum << '\n';
+}
+```
+
+Output:
+
+```
+31
+```
+
+## See also
+
+- [begin](https://json.nlohmann.me/api/basic_json_view/begin/index.md) - returns an iterator to the first element
+- [cend](https://json.nlohmann.me/api/basic_json_view/cend/index.md) - returns a const iterator to one past the last element
+- [`BasicJsonType::cbegin`](https://json.nlohmann.me/api/basic_json/cbegin/index.md) - the corresponding function of `basic_json`
+
+## Version history
+
+- Added in version 3.13.0 unreleased.