1，源码下载：

​​https://github.com/eclipse/paho.mqtt.c​​

解压：

guoyanzhang@debian:~/test$ unzip paho.mqtt.c-master.zip

2，安装编译用的库

guoyanzhang@debian:~/test/paho.mqtt.c-master$ sudo apt-get install build-essential gcc make cmake cmake-gui cmake-curses-gui
guoyanzhang@debian:~/test/paho.mqtt.c-master$ sudo apt-get install fakeroot fakeroot devscripts dh-make lsb-release
guoyanzhang@debian:~/test/paho.mqtt.c-master$ sudo apt-get install libssl-dev
guoyanzhang@debian:~/test/paho.mqtt.c-master$ sudo apt-get install doxygen graphviz

3，编译

guoyanzhang@debian:~/test/paho.mqtt.c-master$ make
guoyanzhang@debian:~/test/paho.mqtt.c-master$ sudo make install
guoyanzhang@debian:~/test/paho.mqtt.c-master$ make html

4，把头文件拷贝到自己要用的地方（这步根据自己的需要选择做）

guoyanzhang@debian:~/test$ cp paho.mqtt.c-master/src/MQTTAsync.h mqtt_h/
guoyanzhang@debian:~/test$ cp paho.mqtt.c-master/src/MQTTClientPersistence.h mqtt_h/
guoyanzhang@debian:~/test$ cp paho.mqtt.c-master/src/MQTTProperties.h mqtt_h/
guoyanzhang@debian:~/test$ cp paho.mqtt.c-master/src/MQTTReasonCodes.h mqtt_h/
guoyanzhang@debian:~/test$ cp paho.mqtt.c-master/src/MQTTSubscribeOpts.h mqtt_h/

5，编译的时候要用-lpaho-mqtt3a

The Paho C client comprises four shared libraries:

libmqttv3a.so - asynchronous (MQTTAsync)
libmqttv3as.so - asynchronous with SSL (MQTTAsync)
libmqttv3c.so - "classic" / synchronous (MQTTClient)
libmqttv3cs.so - "classic" / synchronous with SSL (MQTTClient)

3a是异步，3as是带ssl的异步，3c是同步，3cs是带ssl的同步。

paho是分异步函数和同步函数的，异步函数是非阻塞的，就是把消息发到broker，函数会立即返回，但是消息并未被执行，而是加入一个队列，等待执行，同步函数是阻塞的，等到消息被执行才返回。异步函数也可以加一些其它的参数变成同步阻塞，总体来说，异步函数包含同步函数。