链接Paho MQTT CMake

Question

我正在尝试编译一个使用PAHO-MQTT的简单测试应用程序。我正在运行Antergos Linux x64。我无法编译我的项目，因为PAHO文件没有链接，并且我不知道如何正确地链接它们。这是我正在尝试编译的Main.cpp。

#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "src/MQTTAsync.h"
#include "unistd.h"


#define PUBLISHER 0
volatile MQTTAsync_token deliveredtoken;

int finished = 0;

#if PUBLISHER

#define ADDRESS     "tcp://192.168.2.118:1883"
#define CLIENTID    "Publisher"
#define TOPIC       "test/topic"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

void connlost(void *context, char *cause)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
        int rc;

        printf("\nConnection lost\n");
        printf("     cause: %s\n", cause);

        printf("Reconnecting\n");
        conn_opts.keepAliveInterval = 20;
        conn_opts.cleansession = 1;
        if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start connect, return code %d\n", rc);
                finished = 1;
        }
}


void onDisconnect(void* context, MQTTAsync_successData* response)
{
        printf("Successful disconnection\n");
        finished = 1;
}


void onSend(void* context, MQTTAsync_successData* response)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_disconnectOptions opts = MQTTAsync_disconnectOptions_initializer;
        int rc;

        printf("Message with token value %d delivery confirmed\n", response->token);

        opts.onSuccess = onDisconnect;
        opts.context = client;

        if ((rc = MQTTAsync_disconnect(client, &opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start sendMessage, return code %d\n", rc);
                exit(-1);
        }
}


void onConnectFailure(void* context, MQTTAsync_failureData* response)
{
        printf("Connect failed, rc %d\n", response ? response->code : 0);
        finished = 1;
}


void onConnect(void* context, MQTTAsync_successData* response)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
        MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
        int rc;

        printf("Successful connection\n");

        opts.onSuccess = onSend;
        opts.context = client;

        pubmsg.payload = (void *) PAYLOAD;
        pubmsg.payloadlen = strlen(PAYLOAD);
        pubmsg.qos = QOS;
        pubmsg.retained = 0;
        deliveredtoken = 0;

        if ((rc = MQTTAsync_sendMessage(client, TOPIC, &pubmsg, &opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start sendMessage, return code %d\n", rc);
                exit(-1);
        }
}


int main(int argc, char* argv[])
{
        MQTTAsync client;
        MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
        MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
        MQTTAsync_token token;
        int rc;

        MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);

        MQTTAsync_setCallbacks(client, NULL, connlost, NULL, NULL);

        conn_opts.keepAliveInterval = 20;
        conn_opts.cleansession = 1;
        conn_opts.onSuccess = onConnect;
        conn_opts.onFailure = onConnectFailure;
        conn_opts.context = client;
        if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start connect, return code %d\n", rc);
                exit(-1);
        }

        printf("Waiting for publication of %s\n"
         "on topic %s for client with ClientID: %s\n",
         PAYLOAD, TOPIC, CLIENTID);
        while (!finished)
#if defined(WIN32) || defined(WIN64)
                        Sleep(100);
#else
                        usleep(10000L);
#endif

        MQTTAsync_destroy(&client);
        return rc;
}

#elif PUBLISHER == 0

#define ADDRESS     "tcp://192.168.2.118:1883"
#define CLIENTID    "Subscriber"
#define TOPIC       "test/topic"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

int disc_finished = 0;
int subscribed = 0;

void connlost(void *context, char *cause) {
    MQTTAsync client = (MQTTAsync) context;
    MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
    int rc;

    printf("\nConnection lost\n");
    printf("     cause: %s\n", cause);

    printf("Reconnecting\n");
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;
    if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS) {
        printf("Failed to start connect, return code %d\n", rc);
        finished = 1;
    }
}


int msgarrvd(void *context, char *topicName, int topicLen, MQTTAsync_message *message) {
    int i;
    char *payloadptr;

    printf("Message arrived\n");
    printf("     topic: %s\n", topicName);
    printf("   message: ");

    payloadptr = (char *) message->payload;
    for (i = 0; i < message->payloadlen; i++) {
        putchar(*payloadptr++);
    }
    putchar('\n');
    MQTTAsync_freeMessage(&message);
    MQTTAsync_free(topicName);
    return 1;
}


void onDisconnect(void *context, MQTTAsync_successData *response) {
    printf("Successful disconnection\n");
    disc_finished = 1;
}


void onSubscribe(void *context, MQTTAsync_successData *response) {
    printf("Subscribe succeeded\n");
    subscribed = 1;
}

void onSubscribeFailure(void *context, MQTTAsync_failureData *response) {
    printf("Subscribe failed, rc %d\n", response ? response->code : 0);
    finished = 1;
}


void onConnectFailure(void *context, MQTTAsync_failureData *response) {
    printf("Connect failed, rc %d\n", response ? response->code : 0);
    finished = 1;
}


void onConnect(void *context, MQTTAsync_successData *response) {
    MQTTAsync client = (MQTTAsync) context;
    MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
    MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
    int rc;

    printf("Successful connection\n");

    printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n"
           "Press Q<Enter> to quit\n\n", TOPIC, CLIENTID, QOS);
    opts.onSuccess = onSubscribe;
    opts.onFailure = onSubscribeFailure;
    opts.context = client;

    deliveredtoken = 0;

    if ((rc = MQTTAsync_subscribe(client, TOPIC, QOS, &opts)) != MQTTASYNC_SUCCESS) {
        printf("Failed to start subscribe, return code %d\n", rc);
        exit(-1);
    }
}


int main(int argc, char *argv[]) {
    MQTTAsync client;
    MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
    MQTTAsync_disconnectOptions disc_opts = MQTTAsync_disconnectOptions_initializer;
    MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
    MQTTAsync_token token;
    int rc;
    int ch;

    MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);

    MQTTAsync_setCallbacks(client, NULL, connlost, msgarrvd, NULL);

    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;
    conn_opts.onSuccess = onConnect;
    conn_opts.onFailure = onConnectFailure;
    conn_opts.context = client;
    if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS) {
        printf("Failed to start connect, return code %d\n", rc);
        exit(-1);
    }

    while (!subscribed)
#if defined(WIN32) || defined(WIN64)
        Sleep(100);
#else
        usleep(10000L);
#endif

    if (finished)
        goto exit;

    do {
        ch = getchar();
    } while (ch != 'Q' && ch != 'q');

    disc_opts.onSuccess = onDisconnect;
    if ((rc = MQTTAsync_disconnect(client, &disc_opts)) != MQTTASYNC_SUCCESS) {
        printf("Failed to start disconnect, return code %d\n", rc);
        exit(-1);
    }
    while (!disc_finished)
#if defined(WIN32) || defined(WIN64)
        Sleep(100);
#else
        usleep(10000L);
#endif

    exit:
    MQTTAsync_destroy(&client);
    return rc;
}

#endif

paho mqtt类位于src目录中。在我的CMake中，我尝试这样链接它们：

cmake_minimum_required(VERSION 3.10)
project(MQTT)

set(CMAKE_CXX_STANDARD 11)
file(GLOB src "*.h" "*.c")

add_executable(MQTT main.cpp ${src})

尝试编译时会提示以下异常：

[ 50%] Linking CXX executable MQTT
CMakeFiles/MQTT.dir/main.cpp.o: In function `connlost(user*, char*)':
/home/user/Documents/Projects/MQTT/main.cpp:161: undefined reference to `MQTTAsync_connect'
CMakeFiles/MQTT.dir/main.cpp.o: In function `msgarrvd(user*, char*, int, MQTTAsync_message*)':
/home/user/Documents/Projects/MQTT/main.cpp:181: undefined reference to `MQTTAsync_freeMessage'
/home/user/Documents/Projects/MQTT/main.cpp:182: undefined reference to `MQTTAsync_free'
CMakeFiles/MQTT.dir/main.cpp.o: In function `onConnect(user*, MQTTAsync_successData*)':
/home/user/Documents/Projects/MQTT/main.cpp:226: undefined reference to `MQTTAsync_subscribe'
CMakeFiles/MQTT.dir/main.cpp.o: In function `main':
/home/user/Documents/Projects/MQTT/main.cpp:242: undefined reference to `MQTTAsync_create'
/home/user/Documents/Projects/MQTT/main.cpp:244: undefined reference to `MQTTAsync_setCallbacks'
/home/user/Documents/Projects/MQTT/main.cpp:251: undefined reference to `MQTTAsync_connect'
/home/user/Documents/Projects/MQTT/main.cpp:271: undefined reference to `MQTTAsync_disconnect'
/home/user/Documents/Projects/MQTT/main.cpp:283: undefined reference to `MQTTAsync_destroy'
collect2: error: ld returned 1 exit status
make[3]: *** [CMakeFiles/MQTT.dir/build.make:95: MQTT] Error 1
make[2]: *** [CMakeFiles/Makefile2:68: CMakeFiles/MQTT.dir/all] Error 2
make[1]: *** [CMakeFiles/Makefile2:80: CMakeFiles/MQTT.dir/rule] Error 2
make: *** [Makefile:118: MQTT] Error 2

如何正确链接所有这些文件？

Answer 1

也许你应该以这种方式包含你的.h/.hpp文件：

set (MQTT_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/src/)
target_include_directories (MQTT PUBLIC
                            ${MQTT_INCLUDE_DIR}
                           )

当然，如果您的*.h文件在另一个目录中，您应该更改第一行。

上面的第二行，应该在add_executable之后添加，因为您必须首先创建MQTT目标。

Answer 2

这是一个典型的链接错误，因为您没有指定要链接的库，在本例中为libpaho-mqtt3a.so。在CMakeLists.txt中，在add_executable行之后添加以下行

target_link_libraries(MQTT paho-mqtt3a)

我知道这是一个古老的问题，但张贴答案，因为它可能对相同的问题有用。