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##### boost::mqtt5::mqtt_client::connack_property

Retrieves the value of a specific property from the last `CONNACK` packet received.

###### Synopsis

    template<
        prop::property_type p>
    const auto&
    connack_property(
        std::integral_constant< prop::property_type, p > prop) const;

###### Description

The return type varies according to the property requested. For all properties, the return type will be `std::optional` of their respective value type. For `boost::mqtt5::prop::user_property`, the return type is `std::vector<std::pair<std::string, std::string>>`.

###### Parameters

Name | Description
--- | ---
`prop` | The `boost::mqtt5::connack_props` property value to retrieve.

###### Example

    std::optional<std::string> auth_method = client.connack_property(boost::mqtt5::prop::authentication_method); // ok
    std::optional<std::string> c_type = client.connack_property(boost::mqtt5::prop::content_type); // does not compile, not a CONNACK prop!

###### See Also

See `boost::mqtt5::connack_props` for all eligible properties.