Boost C++ Libraries

The last field in the Variable header of SUBACK packet is a set of Properties. A set contains a Property Length followed by the Properties. A Property consists of an Identifier and a value.

This class extends prop::properties, which provides common functionalities for all property classes. Below is a list of possible SUBACK Properties, along with descriptions of their usage:

Usage

After obtaining an instance of boost::mqtt5::suback_props, the subscript operator can be used to access a Property.

The Identifiers listed in the table above are available within the boost::mqtt5::prop namespace for Property access.

	Note
	When accessing a property value, the subscript operator will return a std::optional of the value type for all properties, except for boost::mqtt5::prop::user_property, where it will return an instance of std::vector<std::pair<std::string, std::string>>.

Example

The following example shows how to set a Property value:

boost::mqtt5::suback_props props;
props[boost::mqtt5::prop::reason_string] = "Some reason...";
props[boost::mqtt5::prop::user_property].emplace_back("name", "value");

The following example shows how to retrieve a Property value:

std::optional<std::string> reason_string = props[boost::mqtt5::prop::reason_string];
if (reason_string.has_value())
    // reason string property was previously set
else
    // reason string property was not set

std::vector<std::pair<std::string, std::string>>& user_props = props[boost::mqtt5::prop::user_property];
if (!user_props.empty())
    // user property was previously set
else
    // user property was not set