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Separate Compilation Mode

Header only mode

By default, async_mqtt operates in header-only mode. Simply #include <async_mqtt/all.hpp> in your source file.

Separate compilation mode

Header-only mode is simple but can significantly increase your project’s build times. In this case, using separate compilation mode could help resolve the issue.

Set the compiler option to define the ASYNC_MQTT_SEPARATE_COMPILATION preprocessor macro for all translation units. This enables separate compilation mode. Then, prepare a source file async_mqtt.cpp as follows:

#include <async_mqtt/src.hpp>

This is for building the library code.

Other source files remain unchanged from the header-only mode. Simply #include <async_mqtt/all.hpp>. Defining ASYNC_MQTT_SEPARATE_COMPILATION automatically removes the library code present in async_mqtt.cpp from async_mqtt/all.hpp. Therefore, once you compile async_mqtt.cpp (which takes a long time due to instantiation), subsequent builds will have faster compilation times.

Examples

Separate compilation mode client

Separate compilation mode endpoint

Library build

This is an alternative method to build a separately compiled library.

  1. Add the ASYNC_MQTT_BUILD_LIB=ON definition to cmake.

  2. Build the target async_mqtt_separate.

For example, on Linux:

cmake -DASYNC_MQTT_BUILD_LIB=ON ..
make async_mqtt_separate

This generates lib/libasync_mqtt_separate.a.

You can link it to your application that is compiled with ASYNC_MQTT_SEPARATE_COMPILATION.

Ensure you provide the same option when building both async_mqtt_separate and your application. If the options differ, linker-related errors may occur.

You can build async_mqtt_separate in parallel. This is faster but requires more memory.

make async_mqtt_separate -j

Customize

By default, the following preprocessor macros are defined. You can customize them by defining the macros with your own values at the top of your library source file.

For example:

#define ASYNC_MQTT_PP_PROTOCOL (your_own_socket)
#include <async_mqtt/src.hpp>

ASYNC_MQTT_PP_ROLE

Defines the instantiation of endpoint roles.

Default value:

(role::client)(role::server)(role::any)

ASYNC_MQTT_PP_SIZE

Defines the instantiation of Packet Identifier sizes.

Default value:

(2)(4)

ASYNC_MQTT_PP_PROTOCOL

Defines the instantiation of endpoint/client underlying layer protocols.

Default value:

(protocol::mqtt)

If ASYNC_MQTT_USE_TLS is defined:

(protocol::mqtt)(protocol::mqtts)

If ASYNC_MQTT_USE_WS is defined:

(protocol::mqtt)(protocol::ws)

If both ASYNC_MQTT_USE_TLS and ASYNC_MQTT_USE_WS are defined:

(protocol::mqtt)(protocol::mqtts)(protocol::ws)(protocol::wss)

ASYNC_MQTT_PP_VERSION

Defines the instantiation of MQTT versions.

Default value:

(protocol_version::v3_1_1)(protocol_version::v5)