json/api/basic_json_view/cbegin.md

nlohmann::basic_json_view::cbegin

iterator cbegin() const noexcept;

Returns an iterator to the first element, in document order. Equivalent to begin(): a view is always read-only, so #!cpp const_iterator and #!cpp 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() 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()`](cend.md) as the
range -- the same way it would for any standard container -- without ever materializing the whole array into a
`BasicJsonType` value.

```cpp
#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:

```json
31

```

See also

• begin - returns an iterator to the first element
• cend - returns a const iterator to one past the last element
• BasicJsonType::cbegin - the corresponding function of basic_json

Version history

• Added in version 3.13.0.