因项目需要，IoT平台需要支持vc++2008接入。因为Paho的c++客户端不支持低版本vc++，所以不得不尝试通过c语言的库实现。
类库下载
从github下载c语言包。例如： eclipse-paho-mqtt-c-win32-1.3.12.zip
https://github.com/eclipse/paho.mqtt.c/releases
类库整合和配置
解压出来的c语言类库包可以看到很多库文件，详情如下图所示。不同的包适用于不同的场景，本案列用了异步客户端，所以用的是paho-mqtt3a这个系列。
配置步骤：
- 拷贝"paho-mqtt3a.dll"到vc++项目的根路径。
- 拷贝"paho-mqtt3a.lib"到vc++项目的"lib"目录（或其他自定义目录）。
- 拷贝"include"目录里面的头文件到vc++项目的"mqtt"目录（或其他自定义目录）。
- 在其他include目录的设置上, 把上一步的包含了mqtt头文件的".\mqtt"目录相对路径输入。
Project(right click)->Properties->Configuration Properties->C/C++->Additional Include Directories
- 在链接配置上, 输入mqtt库文件的相对路径"lib\paho-mqtt3a.lib"。
Project(right click)->Properties->Configuration Properties->Linker->Input->Additional Dependencies
客户端帮助类
这个帮助类会把MQTT客户端封装成单例。为了提高可靠性，启用了buffer消息文件持久化和断线自动重连。
MqttHelper.h
#include "MQTTAsync.h"
#pragma once
#define TIMEOUT 10000L
#define QOS 2
#define ADDRESS "mqtt://xxxx.com:1883"
#define USER "demo"
#define PASSWORD "demo"
class MqttHelper
{
private:
// Private constructor to prevent instantiation
MqttHelper() {
Connected = false;
}
MqttHelper(const MqttHelper&); // Disable copy constructor
MqttHelper& operator=(const MqttHelper&); // Disable assignment operator
MQTTAsync client;
public:
bool Connected;
static MqttHelper& getInstance() {
static MqttHelper instance;
return instance;
}
public:
bool Connect();
void Close();
bool Subcribe(char* topic);
bool Publish(char* topic, void*payload, int payloadLength);
bool Publish(char* topic, void*payload, int payloadLength, int qos);
int OnMsgReceived(void *context, char *topicName, int topicLen, MQTTAsync_message *message);
void OnMsgPublished(void* context, MQTTAsync_token token);
void OnConnected(void* context, MQTTAsync_successData* response);
private:
char* GetClientId();
};
MqttHelper.cpp
#include "StdAfx.h"
#include "MqttHelper.h"
#include <windows.h>
void OnSuccessCallback(void* context, MQTTAsync_successData* response) {
MqttHelper* mqttHelper = static_cast<MqttHelper*>(context);
mqttHelper->OnConnected(context, response);
}
int OnMessageArrived(void* context, char* topicName, int topicLen, MQTTAsync_message* message){
MqttHelper* mqttHelper = static_cast<MqttHelper*>(context);
return mqttHelper->OnMsgReceived(context, topicName, topicLen, message);
}
void OnDeliveryComplete(void* context, MQTTAsync_token token){
MqttHelper* mqttHelper = static_cast<MqttHelper*>(context);
mqttHelper->OnMsgPublished(context, token);
}
bool MqttHelper::Connect(){
if (Connected){
return true;
}
MQTTAsync_create(&client, ADDRESS, GetClientId(), MQTTCLIENT_PERSISTENCE_DEFAULT, NULL);
if (MQTTAsync_setCallbacks(client, client, NULL,
OnMessageArrived,OnDeliveryComplete) != MQTTASYNC_SUCCESS)
{
return false;
}
MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 0;
conn_opts.username = USER;
conn_opts.password = PASSWORD;
conn_opts.automaticReconnect = 1;
conn_opts.onSuccess = OnSuccessCallback;
conn_opts.MQTTVersion = MQTTVERSION_3_1_1;
int rc = MQTTAsync_connect(client, &conn_opts);
if (rc != MQTTASYNC_SUCCESS)
{
return false;
}
Connected = true;
return true;
}
void MqttHelper::Close(){
if (client != NULL)
{
MQTTAsync_disconnect(client, NULL);
MQTTAsync_destroy(&client);
}
}
bool MqttHelper::Subcribe(char* topic){
int rc = MQTTAsync_subscribe(client, topic, QOS, NULL);
if (rc != MQTTASYNC_SUCCESS)
{
return false;
}
return true;
}
bool MqttHelper::Publish(char* topic, void*payload, int payloadLength){
return Publish(topic, payload, payloadLength, QOS);
}
bool MqttHelper::Publish(char* topic, void*payload, int payloadLength, int qos){
MQTTAsync_responseOptions pub_opts = MQTTAsync_responseOptions_initializer;
MQTTAsync_message pub_msg = MQTTAsync_message_initializer;
pub_msg.payload = payload;
pub_msg.payloadlen = payloadLength;
pub_msg.qos = qos;
pub_msg.retained = 0;
int rc = MQTTAsync_sendMessage(client, topic, &pub_msg, &pub_opts);
return rc == MQTTASYNC_SUCCESS;
}
char* MqttHelper::GetClientId(){
TCHAR computerName[MAX_COMPUTERNAME_LENGTH + 1];
DWORD size = sizeof(computerName) / sizeof(computerName[0]);
if (!GetComputerName(computerName, &size)){
lstrcpy(computerName, _T("unknown"));
}
TCHAR path[MAX_PATH];
TCHAR* processName;
if (GetModuleFileName(NULL, path, sizeof(path)) != 0) {
processName = _tcsrchr(path, '\\');
if (processName != NULL)
processName++; // Move past the backslash
else
processName = path;
}
TCHAR clientId[MAX_PATH];
lstrcpy(clientId, computerName);
lstrcat(clientId, _T("."));
lstrcat(clientId, processName);
int charArrayLength = WideCharToMultiByte(
CP_ACP, // Code page for the conversion
0, // Conversion flags (0 for default behavior)
clientId, // Source TCHAR array
-1, // Length of the source TCHAR array (-1 for null-terminated)
NULL, // Destination char array
0, // Size of the destination char array
NULL, // Default character used for conversion errors (optional)
NULL // Indicates if the function used a default character (optional)
);
if (charArrayLength > 0) {
char* charArray = new char[charArrayLength];
WideCharToMultiByte(
CP_ACP, // Code page for the conversion
0, // Conversion flags (0 for default behavior)
clientId, // Source TCHAR array
-1, // Length of the source TCHAR array (-1 for null-terminated)
charArray, // Destination char array
charArrayLength, // Size of the destination char array
NULL, // Default character used for conversion errors (optional)
NULL // Indicates if the function used a default character (optional)
);
return charArray;
}
return "unknown";
}
int MqttHelper::OnMsgReceived(void *context, char *topicName, int topicLen, MQTTAsync_message *message){
MQTTAsync client = (MQTTAsync)context;
printf("Message arrived\n");
printf(" topic: %s\n", topicName);
printf(" message: %.*s\n", message->payloadlen, (char*)message->payload);
MQTTAsync_freeMessage(&message);
MQTTAsync_free(topicName);
return 1;
}
void MqttHelper::OnMsgPublished(void* context, MQTTAsync_token token){
printf("Message arrived\n");
printf(" token: %d\n", token);
}
void MqttHelper::OnConnected(void* context, MQTTAsync_successData* response){
printf("client connected\n");
MQTTAsync client = (MQTTAsync)context;
//subcribe topic
/*int rc = MQTTAsync_subscribe(client, "demo/in", QOS, NULL);
if (rc != MQTTASYNC_SUCCESS)
{
printf("subscribe success\n");
}
else
{
printf("subscribe failed\n");
}*/
}
把以上代码整合到你的项目，然后就可以通过调用"MqttHelper::getInstance().Publish("demo/test", byteData, strlen(byteData))"来发送消息了。
用MQTTX辅助调试
- 下载并安装MQTTX。
https://mqttx.app/ - 创建连接到MQTT broker.
- 连接并订阅主题"demo/#"。
转载请注明出处: https://i.cnblogs.com/posts/edit;postId=17611371