Qt工程使用MQTT-C库与mqtt服务器数据通信

news2025/11/4 11:53:08

实现mqtt订阅与发布话题，与mqtt服务器进行数据通信

编译环境：Qt5.15.2 + vs2019

需要mqttc库：mqttc.lib, mqttc.dll（根据MQTT-C源码编译出来的库，参考cmake编译MQTT-C源码-CSDN博客）

一、Qt pro文件编写

在Demo中创建mqtt-c文件夹，将mqttc库放在指定文件夹下，MQTT-C头文件包括mqtt_pal.h与mqtt.h。

QT += quick

CONFIG += c++17

SOURCES += \
        main.cpp

RESOURCES += qml.qrc

INCLUDEPATH += $$PWD/ mqtt-c/include \
                $$PWD/mqtt-c/templates

# 链接静态库
LIBS += -L$$PWD/mqtt-c/lib -lmqttc

DebugBuild {
    DESTDIR  = $${OUT_PWD}/debug
} else {
    DESTDIR  = $${OUT_PWD}/release
}

win32 {
    message("Building for MQTT-C Windows")
    # MQTT文件夹名
    MQTT_PATH = mqtt-c

    DESTDIR_WIN = $$replace(DESTDIR, "/", "\\")
    message($$DESTDIR_WIN)

    # 拷贝动态库
    MQTTC_DLL = \
        $$PWD\\$$MQTT_PATH\\bin\\mqttc.dll
    # 拷贝动态库到exe可执行文件同级文件夹下
    QMAKE_POST_LINK += $$escape_expand(\\n) $$QMAKE_COPY \"$$MQTTC_DLL\" \"$$DESTDIR_WIN\"
}

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

二、实现Mqtt发布、订阅话题功能，与mqtt服务器数据通信。

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <iostream>

#include "posix_sockets.h"
#include "mqtt.h"  // 包含MQTT库的头文件

const char* DEFAULT_HOST = "47.120.xx.xxx"; // 替换成mqtt服务器地址
const char* DEFAULT_PORT = "1883";
const char* TOPIC = "testtopic/MAV";

void publish_callback(void** unused, struct mqtt_response_publish *published) {
    // 收到发布消息时的回调
    char* topic_name = (char*)malloc(published->topic_name_size + 1);
    memcpy(topic_name, published->topic_name, published->topic_name_size);
    topic_name[published->topic_name_size] = '\0';

    // 修复收到的多余字符
    char* message = (char*)malloc(published->application_message_size + 1);
    memcpy(message, published->application_message, published->application_message_size);
    message[published->application_message_size] = '\0';  // 添加结束符
    
std::cout << "Received message on topic: " << std::string((const char*)published->topic_name, published->topic_name_size)
              << ", message: " << message << std::endl;
}

DWORD WINAPI client_refresher(LPVOID client) {
    while (1) {
        mqtt_sync((struct mqtt_client*)client);
        Sleep(100);
    }
    return 0;
}

int main(int argc, char *argv[]) {
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;

    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2,2), &wsaData) != 0) {
        qDebug() << "WSAStartup failed.";
        return -1;
    }

    //SOCKET sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    int sockfd = open_nb_socket(DEFAULT_HOST, DEFAULT_PORT);
    if (sockfd == INVALID_SOCKET) {
        qDebug() << "Socket creation failed.";
        WSACleanup();
        return -1;
    }

    struct mqtt_client client;
    uint8_t sendbuf[2048];
    uint8_t recvbuf[1024];
    mqtt_init(&client, sockfd, sendbuf, sizeof(sendbuf), recvbuf, sizeof(recvbuf), publish_callback);

    /* Create an anonymous session */
    const char* client_id = NULL;
    /* Ensure we have a clean session */
    uint8_t connect_flags = MQTT_CONNECT_CLEAN_SESSION;
    /* Send connection request to the broker. */
    mqtt_connect(&client, client_id, NULL, NULL, 0, NULL, NULL, connect_flags, 400);

    /* check that we don't have any errors */
    if (client.error != MQTT_OK) {
        qDebug() << "error:" << mqtt_error_str(client.error);
        //fprintf(stderr, "error: %s\n", mqtt_error_str(client.error));
    }

    // 订阅
    mqtt_subscribe(&client, TOPIC, 0);

    HANDLE refresh_thread = CreateThread(NULL, 0, client_refresher, &client, 0, NULL);
    if (refresh_thread == NULL) {
        qDebug() << "Failed to start client daemon thread.";
        mqtt_disconnect(&client);
        closesocket(sockfd);
        WSACleanup();
        return -1;
    }

    // 发布
    const char* _mockData = "CusData";
    mqtt_publish(&client, TOPIC, _mockData, strlen(_mockData), MQTT_PUBLISH_QOS_0);

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty()) {
        qDebug() << "Failed to load QML.";
        return -1;
    }

    int result = app.exec();

    WaitForSingleObject(refresh_thread, INFINITE);
    CloseHandle(refresh_thread);
    mqtt_disconnect(&client);
    closesocket(sockfd);
    WSACleanup();

    return result;
}

三、编译报错

1、“close”: 找不到标识符报错
..\Qt-MQTT-C-Demo\mqtt-c\templates\posix_sockets.h(46): error C3861: “close”: 找不到标识符
原因是posix_sockets.h源码只适配了Linux，需要做Windows端的适配。