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1.c/c++ mqtt相关库

• paho MQTT C/C++ 库
• mosquitto C/C++库

本文介绍 paho_mqtt_c++库使用示例

2.安装

1.下载编译

git clone https://github.com/eclipse/paho.mqtt.cpp
cd paho.mqtt.cpp
git checkout v1.4.0 # 可以按官网教程, 更新到最新版本git submodule init
git submodule updatecmake -Bbuild -H. -DPAHO_WITH_MQTT_C=ON -DPAHO_BUILD_EXAMPLES=ON
cd build
make -j4
sudo make install

2.安装文件

c++库

libpaho-mqttpp3.so

c库

libpaho-mqtt3a.so
libpaho-mqtt3c.so

头文件

/usr/local/include/MQTTAsync.h
/usr/local/include/MQTTClient.h
/usr/local/include/MQTTClientPersistence.h
/usr/local/include/MQTTProperties.h
/usr/local/include/MQTTReasonCodes.h
/usr/local/include/MQTTSubscribeOpts.h
/usr/local/include/MQTTExportDeclarations.h
…

3.编译链接选项

由头文件位置可知, 编译选项
-I /usr/local/include

由库文件位置可以, 链接选项
-L /usr/local/lib
-lpaho-mqttpp3 -lpaho-mqtt3a -lpaho-mqtt3c

3.mqtt发布_订阅示例

1.订阅发布代码

1_mqtt_发布.cc

#include <iostream>
#include <cstdlib>
#include <string>
#include <thread> // For sleep
#include <atomic>
#include <chrono>
#include <cstring>
#include <unistd.h>
#include <stdio.h>
#include "mqtt/async_client.h"using namespace std;const string DFLT_SERVER_ADDRESS{"mqtt://localhost:1883"};const string TOPIC{"test"};
const int QOS = 1;const char *PAYLOADS[] = {"Hello World!","Hi there!","Is anyone listening?","Someone is always listening.",nullptr};const auto TIMEOUT = std::chrono::seconds(10);int main(int argc, char *argv[])
{string address = (argc > 1) ? string(argv[1]) : DFLT_SERVER_ADDRESS;cout << "Initializing for server '" << address << "'..." << endl;mqtt::async_client cli(address, "");cout << "  ...OK" << endl;try{cout << "\nConnecting..." << endl;cli.connect()->wait();cout << "  ...OK" << endl;cout << "\nPublishing messages..." << endl;mqtt::topic top(cli, "test", QOS);mqtt::token_ptr tok;size_t i = 0;char buf[64];while (i < 1000){snprintf(buf, sizeof(buf), "%ld %s", i, PAYLOADS[i % 4]);tok = top.publish(buf);sleep(1);i++;}tok->wait(); // Just wait for the last one to complete.cout << "OK" << endl;// Disconnectcout << "\nDisconnecting..." << endl;cli.disconnect()->wait();cout << "  ...OK" << endl;}catch (const mqtt::exception &exc){cerr << exc << endl;return 1;}return 0;
}

2_mqtt_订阅.cc

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <unistd.h>
#include <mqtt/async_client.h>const std::string SERVER_ADDRESS("tcp://localhost:1883");
const std::string CLIENT_ID("paho_cpp_async");
const std::string TOPIC("test");class callback : public virtual mqtt::callback, public virtual mqtt::iaction_listener
{
private:mqtt::async_client &client_;public:callback(mqtt::async_client &client) : client_(client) {}void connection_lost(const std::string &cause) override{std::cout << "\nConnection lost" << std::endl;if (!cause.empty())std::cout << "\tcause: " << cause << std::endl;}void delivery_complete(mqtt::delivery_token_ptr token) override {}void message_arrived(const mqtt::const_message_ptr msg) override{std::cout << "Message arrived: " << msg->get_payload_str() << std::endl;}void on_failure(const mqtt::token &tok) override{std::cout << "Connection attempt failed" << std::endl;}void on_success(const mqtt::token &tok) override{std::cout << "Connection attempt successful" << std::endl;// 发布消息mqtt::message_ptr pubmsg = mqtt::make_message(TOPIC, "Hello from Paho C++");pubmsg->set_qos(1);client_.publish(pubmsg);}
};int main(int argc, char *argv[])
{mqtt::async_client client(SERVER_ADDRESS, CLIENT_ID);callback cb(client);client.set_callback(cb);mqtt::connect_options connOpts;connOpts.set_clean_session(true);try{std::cout << "Connecting to the MQTT server..." << std::endl;mqtt::token_ptr conntok = client.connect(connOpts);conntok->wait();std::cout << "Connected!" << std::endl;// 订阅消息client.subscribe(TOPIC, 1);while (true){// 持续监听消息usleep(1000000);}}catch (const mqtt::exception &exc){std::cerr << "Error: " << exc.what() << std::endl;return 1;}return 0;
}

2.构建脚本: SConstruct

env = Environment()
env["PROGSUFFIX"] = ".out"  # 可执行文件后缀.out
env["CCFLAGS"] = " -g3 -O0 -Wall"  # gdb 调试
paho_mqtt_libs = ["paho-mqttpp3", "paho-mqtt3c", "paho-mqtt3a"]
env["LIBS"] = paho_mqtt_libs
env.Program("1_mqtt_发布.cc")
env.Program("2_mqtt_订阅.cc")

3.编译

scons
scons: Reading SConscript files …
scons: done reading SConscript files.
scons: Building targets …
g++ -o 1_mqtt_发布.o -c -g3 -O0 -Wall 1_mqtt_发布.cc
g++ -o 1_mqtt_发布.out 1_mqtt_发布.o -lpaho-mqttpp3 -lpaho-mqtt3c -lpaho-mqtt3a
g++ -o 2_mqtt_订阅.o -c -g3 -O0 -Wall 2_mqtt_订阅.cc
g++ -o 2_mqtt_订阅.out 2_mqtt_订阅.o -lpaho-mqttpp3 -lpaho-mqtt3c -lpaho-mqtt3a
scons: done building targets.

4.测试验证

终端1: ./1_mqtt_发布.out
终端2: ./2_mqtt_订阅.out
结果: 终端2 订阅端接收到的消息

./2_mqtt_订阅.out
Connecting to the MQTT server…
Connected!
Message arrived: 5 Hi there!
Message arrived: 6 Is anyone listening?
Message arrived: 7 Someone is always listening.
Message arrived: 8 Hello World!
Message arrived: 9 Hi there!
Message arrived: 10 Is anyone listening?
Message arrived: 11 Someone is always listening.
Message arrived: 12 Hello World!
Message arrived: 13 Hi there!
Message arrived: 14 Is anyone listening?
Message arrived: 15 Someone is always listening.
Message arrived: 16 Hello World!
Message arrived: 17 Hi there!

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