# nlohmann::basic_json_view::get_to

```
template<typename T>
T& get_to(T& v) const;
```

Converts the value to `T` and stores it in `v`, in one of two ways:

- For the types that [`get<T>()`](https://json.nlohmann.me/api/basic_json_view/get/index.md) converts directly -- arithmetic types, `bool`, `std::nullptr_t`, [`string_view_t`](https://json.nlohmann.me/api/basic_json_view/#member-types), `std::basic_string`, `BasicJsonType`, `basic_json_view`, `std::vector`, and `std::map`/`std::unordered_map` with string keys -- `v` is assigned: `v = get<T>()`.
- For every other type, the subtree is built into a `BasicJsonType` value and `materialize().get_to(v)` is called, i.e. `from_json()` is invoked with the existing `v`, exactly as [`BasicJsonType::get_to()`](https://json.nlohmann.me/api/basic_json/get_to/index.md) does.

## Template parameters

`T` : the type to convert the value to

## Parameters

`v` (out) : the variable to store the converted value in

## Return value

`v`, allowing calls to chain

## Exception safety

- For the directly converted types: strong exception safety. If an exception is thrown, `v` is not modified.
- For every other type: as for [`BasicJsonType::get_to()`](https://json.nlohmann.me/api/basic_json/get_to/index.md). `materialize()` throws before `v` is touched, but a `from_json()` that throws may leave `v` partly modified.

## Exceptions

- For the directly converted types: whatever [`get<T>()`](https://json.nlohmann.me/api/basic_json_view/get/index.md) throws for the same value and `T`.
- For every other type: whatever [`materialize()`](https://json.nlohmann.me/api/basic_json_view/materialize/index.md) and [`BasicJsonType::get_to()`](https://json.nlohmann.me/api/basic_json/get_to/index.md) throw.

## Complexity

- For the directly converted types: whatever [`get<T>()`](https://json.nlohmann.me/api/basic_json_view/get/index.md) has for the same `T`.
- For every other type: that of [`materialize()`](https://json.nlohmann.me/api/basic_json_view/materialize/index.md), plus that of [`BasicJsonType::get_to()`](https://json.nlohmann.me/api/basic_json/get_to/index.md).

## Notes

The difference between the two ways matters for a `from_json()` that sets only the fields present in the JSON: since it runs on the existing `v`, the other fields of `v` keep their values, whereas assigning `get<T>()` would replace them with those of a default-constructed `T`.

## Examples

Example

The example below reads several fields of a service configuration directly into existing variables, then uses the returned reference to fold the `host`/`port` pair into a single string in the same expression.

```
#include <iostream>
#include <nlohmann/json_view.hpp>
#include <string>

using json_document = nlohmann::json_document;
using json_view = nlohmann::json_view;

int main()
{
    json_document doc = json_document::parse(R"({"host": "db.example.com", "port": 5432, "ssl": true})");
    const json_view config = doc.root();

    // get_to() writes directly into existing variables -- handy for filling
    // in the members of a struct one field at a time, without an
    // intermediate value from get<T>() for each one
    std::string host;
    int port = 0;
    bool ssl = false;
    config["host"].get_to(host);
    config["port"].get_to(port);
    config["ssl"].get_to(ssl);
    std::cout << host << ':' << port << (ssl ? " (tls)" : "") << '\n';

    // the return value is a reference to the argument, so a call can be
    // used directly in a larger expression
    std::string other_host;
    std::cout << config["host"].get_to(other_host).size() << '\n';
}
```

Output:

```
db.example.com:5432 (tls)
14
```

## See also

- [get](https://json.nlohmann.me/api/basic_json_view/get/index.md) - convert the value to a given type
- [`BasicJsonType::get_to`](https://json.nlohmann.me/api/basic_json/get_to/index.md) - the corresponding function of `basic_json`

## Version history

- Added in version 3.13.0 unreleased.