C 接入该如何进行？_问答-阿里云开发者社区

注意：
本文给出的实例均基于 Eclipse Paho C SDK 实现，该 SDK 下载请参见 MQTT 接入准备。如使用其他第三方的客户端，请适当修改。

1. 资源申请

使用 MQ 提供的 MQTT 服务，首先需要核实应用中使用的 Topic 资源是否已经申请，如果没有请先去控制台申请 Topic，Group ID 等资源。
申请资源时需要根据需求选择对应的 Region，例如，MQTT 需要使用华北 2 的接入点，那么 Topic 等资源就在华北 2 申请，资源申请具体请参见申请 MQ 资源。
注意：MQTT 使用的多级子 Topic 不需要申请，代码里直接使用即可，没有限制。

2. C 客户端依赖

Paho MQTT C 客户端 SDK 从官网下载源码后,参考文档进行编译安装。可能需要安装以下开发库和工具。

openssl：用于签名计算。
cmake：用于编译示例程序，实际也可以根据习惯选用其他编译工具。

3. MQTT 收发消息

本段示例代码演示如何使用 C 客户端收发 MQTT 消息，其中编译工具使用CMake。
CMakeLists.txt 文件

cmake_minimum_required(VERSION 3.7)
project(mqttdemo)
INCLUDE_DIRECTORIES(
.
${CMAKE_SOURCE_DIR}/src
${CMAKE_BINARY_DIR}
)
SET(CMAKE_BUILD_TYPE "Debug")
SET(CMAKE_CXX_FLAGS_DEBUG "$ENV{CXXFLAGS} -O0 -Wall -g2 -ggdb")
SET(CMAKE_CXX_FLAGS_RELEASE "$ENV{CXXFLAGS} -O3 -Wall")
set(CMAKE_C_STANDARD 99)
add_executable(mqttDemo mqttDemo.c)
TARGET_LINK_LIBRARIES(mqttDemo crypto)
TARGET_LINK_LIBRARIES(mqttDemo paho-mqtt3a)

收发消息程序：

#include "MQTTAsync.h"
#include <signal.h>
#include <memory.h>
#include <stdlib.h>
#include <unistd.h>
#include <openssl/hmac.h>
#include <openssl/bio.h>
volatile int connected = 0;
char *topic;
char *userName;
char *passWord;
int messageDeliveryComplete(void *context, MQTTAsync_token token) {
/* not expecting any messages */
printf("send message %d success\n", token);
return 1;
}
int messageArrived(void *context, char *topicName, int topicLen, MQTTAsync_message *m) {
/* not expecting any messages */
printf("recv message from %s ,body is %s\n", topicName, (char *) m->payload);
return 1;
}
void onConnectFailure(void *context, MQTTAsync_failureData *response) {
connected = 0;
printf("connect failed, rc %d\n", response ? response->code : -1);
MQTTAsync client = (MQTTAsync) context;
}
void onSubcribe(void *context, MQTTAsync_successData *response) {
printf("subscribe success \n");
}
void onConnect(void *context, MQTTAsync_successData *response) {
connected = 1;
printf("connect success \n");
MQTTAsync client = (MQTTAsync) context;
//do sub when connect success
MQTTAsync_responseOptions sub_opts = MQTTAsync_responseOptions_initializer;
sub_opts.onSuccess = onSubcribe;
int rc = 0;
if ((rc = MQTTAsync_subscribe(client, topic, 1, ⊂_opts)) != MQTTASYNC_SUCCESS) {
printf("Failed to subscribe, return code %d\n", rc);
}
}
void onDisconnect(void *context, MQTTAsync_successData *response) {
connected = 0;
printf("connect lost \n");
}
void onPublishFailure(void *context, MQTTAsync_failureData *response) {
printf("Publish failed, rc %d\n", response ? -1 : response->code);
}
int success = 0;
void onPublish(void *context, MQTTAsync_successData *response) {
printf("send success %d\n", ++success);
}
void connectionLost(void *context, char *cause) {
connected = 0;
MQTTAsync client = (MQTTAsync) context;
MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
int rc = 0;
printf("Connecting\n");
conn_opts.keepAliveInterval = 10;
conn_opts.cleansession = 1;
conn_opts.username = userName;
conn_opts.password = passWord;
conn_opts.onSuccess = onConnect;
conn_opts.onFailure = onConnectFailure;
conn_opts.context = client;
conn_opts.ssl = NULL;
if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS) {
printf("Failed to start connect, return code %d\n", rc);
exit(EXIT_FAILURE);
}
}
int main(int argc, char **argv) {
MQTTAsync_disconnectOptions disc_opts = MQTTAsync_disconnectOptions_initializer;
MQTTAsync client;
//MQTT使用的Topic，其中第一级父Topic需要在MQ控制台先申请
topic = "XXXXX";
//MQTT的接入域名，在MQ控制台购买付费实例后即分配该域名
char *host = "XXX.mqtt.aliyuncs.com";
//MQTT客户端分组Id，需要先在MQ控制台申请
char *groupId = "GID_XXXXXX";
//MQTT客户端设备Id，用户自行生成，需要保证对于所有TCP连接全局唯一
char *deviceId = "XXXXXXX";
//帐号AK
char *accessKey = "XXXXXXX";
//帐号SK
char *secretKey = "XXXXXXX";
//服务端口，使用MQTT协议时设置1883,其他协议参考文档选择合适端口
int port = 1883;
//QoS，消息传输级别，参考文档选择合适的值
int qos = 1;
//cleanSession，是否设置持久会话，如果需要离线消息则cleanSession必须是false，QoS必须是1
int cleanSession = 0;
int rc = 0;
char tempData[100];
int len = 0;
HMAC(EVP_sha1(), secretKey, strlen(secretKey), groupId, strlen(groupId), tempData, &len);
char resultData[100];
int passWordLen = EVP_EncodeBlock((unsigned char *) resultData, tempData, len);
resultData[passWordLen] = '\0';
printf("passWord is %s", resultData);
userName = accessKey;
passWord = resultData;
//1.create client
MQTTAsync_createOptions create_opts = MQTTAsync_createOptions_initializer;
create_opts.sendWhileDisconnected = 0;
create_opts.maxBufferedMessages = 10;
char url[100];
sprintf(url, "%s:%d", host, port);
char clientIdUrl[64];
sprintf(clientIdUrl, "%s@@@%s", groupId, deviceId);
rc = MQTTAsync_createWithOptions(&client, url, clientIdUrl, MQTTCLIENT_PERSISTENCE_NONE, NULL, &create_opts);
rc = MQTTAsync_setCallbacks(client, client, connectionLost, messageArrived, NULL);
//2.connect to server
MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
conn_opts.keepAliveInterval = 90;
conn_opts.cleansession = cleanSession;
conn_opts.username = userName;
conn_opts.password = passWord;
conn_opts.onSuccess = onConnect;
conn_opts.onFailure = onConnectFailure;
conn_opts.context = client;
conn_opts.ssl = NULL;
conn_opts.automaticReconnect = 1;
conn_opts.connectTimeout = 3;
if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS) {
printf("Failed to start connect, return code %d\n", rc);
exit(EXIT_FAILURE);
}
//3.publish msg
MQTTAsync_responseOptions pub_opts = MQTTAsync_responseOptions_initializer;
pub_opts.onSuccess = onPublish;
pub_opts.onFailure = onPublishFailure;
for (int i = 0; i < 1000; i++) {
do {
char data[100];
sprintf(data, "hello mqtt demo");
rc = MQTTAsync_send(client, topic, strlen(data), data, qos, 0, &pub_opts);
sleep(1);
} while (rc != MQTTASYNC_SUCCESS);
}
sleep(1000);
disc_opts.onSuccess = onDisconnect;
if ((rc = MQTTAsync_disconnect(client, &disc_opts)) != MQTTASYNC_SUCCESS) {
printf("Failed to start disconnect, return code %d\n", rc);
exit(EXIT_FAILURE);
}
while (connected)
sleep(1);
MQTTAsync_destroy(&client);
return EXIT_SUCCESS;
}

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