api/basic_json_view/get_to.md

# <small>nlohmann::basic_json_view::</small>get_to

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

## Complexity

- For the directly converted types: whatever [`get<T>()`](get.md) has for the same `T`.
- For every other type: that of [`materialize()`](materialize.md), plus that of
  [`BasicJsonType::get_to()`](../basic_json/get_to.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 `#!cpp host`/`#!cpp port` pair into a single string in the same expression.

    ```cpp
    #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:

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

## See also

- [get](get.md) - convert the value to a given type
- [`BasicJsonType::get_to`](../basic_json/get_to.md) - the corresponding function of `basic_json`

## Version history

- Added in version 3.13.0.