D++ (DPP)
C++ Discord API Bot Library
Using Callback Functions

When you create or get an object from Discord, you send the request to its API and in return you get either an error or the object you requested/created. You can pass a function to API calls as the callback function. This means that when the request completes, and you get a response from the API, your callback function executes. You must be careful with lambda captures! Good practice would be not capturing variables by reference unless you have to, since when the request completes and the function executes, the variables can already be destructed. Advanced reference can be found here. Now, let's see callback functions in action:

#include <dpp/dpp.h>
int main() {
/* the second argument is a bitmask of intents - i_message_content is needed to get messages */
/* The event is fired when someone issues your commands */
bot.on_slashcommand([&bot](const dpp::slashcommand_t& event) {
if (event.command.get_command_name() == "msgs-get") {
int64_t limit = std::get<int64_t>(event.get_parameter("quantity"));
/* get messages using ID of the channel the command was issued in */
bot.messages_get(event.command.channel_id, 0, 0, 0, limit, [event](const dpp::confirmation_callback_t& callback) {
if (callback.is_error()) { /* catching an error to log it */
std::cout << callback.get_error().message << std::endl;
return;
}
auto messages = callback.get<dpp::message_map>();
/* std::get<dpp::message_map>(callback.value) would give the same result */
std::string contents;
for (const auto& x : messages) { /* here we iterate through the dpp::message_map we got from callback... */
contents += x.second.content + '\n'; /* ...where x.first is ID of the current message and x.second is the message itself. */
}
event.reply(contents); /* we will see all those messages we got, united as one! */
});
} else if (event.command.get_command_name() == "channel-create") {
/* create a text channel */
.set_name("test")
bot.channel_create(channel, [&bot, event](const dpp::confirmation_callback_t& callback) -> void {
if (callback.is_error()) { /* catching an error to log it */
bot.log(dpp::loglevel::ll_error, callback.get_error().message);
return;
}
auto channel = callback.get<dpp::channel>();
/* std::get<dpp::channel>(callback.value) would give the same result */
/* reply with the created channel information */
dpp::message message = dpp::message("The channel's name is `" + channel.name + "`, ID is `" + std::to_string(channel.id) + " and type is `" + std::to_string(channel.get_type()) + "`.");
/* note that channel types are represented as numbers */
event.reply(message);
});
} else if (event.command.get_command_name() == "msg-error") {
bot.message_get(0, 0, [event](const dpp::confirmation_callback_t& callback) -> void {
/* the error will occur since there is no message with ID '0' that is in a channel with ID '0' (I'm not explaining why) */
if (callback.is_error()) {
event.reply(callback.get_error().message);
return;
}
/* we won't be able to get here because of the return; statement */
auto message = callback.get<dpp::message>();
event.reply(message);
});
}
});
bot.on_ready([&bot](const dpp::ready_t& event) {
if (dpp::run_once <struct register_global_commands>()) {
dpp::slashcommand msgs_get("msgs-get", "Get messages", bot.me.id);
constexpr int64_t min_val{1};
constexpr int64_t max_val{100};
msgs_get.add_option(
dpp::command_option(dpp::co_integer, "quantity", "Quantity of messages to get. Max - 100.")
.set_min_value(min_val)
.set_max_value(max_val)
);
dpp::slashcommand channel_create("channel-create", "Create a channel", bot.me.id);
dpp::slashcommand msg_error("msg-error", "Get an error instead of message :)", bot.me.id);
bot.global_bulk_command_create({ msgs_get, channel_create, msg_error });
}
});
bot.start(dpp::st_wait);
return 0;
}

This is the result:

dpp::confirmation_callback_t::get
T get() const
Get the stored value via std::get.
Definition: restresults.h:342
dpp::managed::id
snowflake id
Unique ID of object set by Discord. This value contains a timestamp, worker ID, internal server ID,...
Definition: managed.h:79
dpp::i_default_intents
@ i_default_intents
Default D++ intents (all non-privileged intents).
Definition: intents.h:172
dpp::slashcommand_t
User has issued a slash command.
Definition: dispatcher.h:715
dpp::st_wait
@ st_wait
Wait forever on a condition variable. The cluster will spawn threads for each shard and start() will ...
Definition: cluster.h:101
dpp::channel
A definition of a discord channel. There are one of these for every channel type except threads....
Definition: channel.h:360
dpp::interaction::guild_id
snowflake guild_id
Optional: the guild it was sent from.
Definition: appcommand.h:989
dpp::channel::get_type
channel_type get_type() const
Get the channel type.
dpp::confirmation_callback_t::is_error
bool is_error() const
Returns true if the call resulted in an error rather than a legitimate value in the confirmation_call...
dpp::message
Represents messages sent and received on Discord.
Definition: message.h:1772
dpp::co_integer
@ co_integer
An integer value.
Definition: appcommand.h:88
dpp::interaction_create_t::command
interaction command
command interaction
Definition: dispatcher.h:698
dpp::i_message_content
@ i_message_content
Intent for receipt of message content.
Definition: intents.h:152
dpp::slashcommand
Represents an application command, created by your bot either globally, or on a guild.
Definition: appcommand.h:1358
dpp::channel::name
std::string name
Channel name (1-100 characters).
Definition: channel.h:384
dpp::utility::cout_logger
std::function< void(const dpp::log_t &)> DPP_EXPORT cout_logger()
Get a default logger that outputs to std::cout. e.g.
Definition: dispatcher.h:228
dpp::interaction::get_command_name
std::string get_command_name() const
Get the command name for a command interaction.
dpp::interaction_create_t::reply
void reply(command_completion_event_t callback=utility::log_error()) const
Acknowledge interaction without displaying a message to the user, for use with button and select menu...
dpp::command_option
Each command option is a command line parameter. It can have a type (see dpp::command_option_type),...
Definition: appcommand.h:222
dpp::channel::set_name
channel & set_name(const std::string &name)
Set name of this channel object.
dpp::cluster
The cluster class represents a group of shards and a command queue for sending and receiving commands...
Definition: cluster.h:99
dpp::confirmation_callback_t
The results of a REST call wrapped in a convenient struct.
Definition: restresults.h:274
dpp::channel::set_guild_id
channel & set_guild_id(const snowflake guild_id)
Set guild_id of this channel object.
dpp::ready_t
Session ready.
Definition: dispatcher.h:981
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