上一篇文章已经将mosquitto移植到了arm平台上，现在将使用mosquitto完成mqtt客服端的demo，了解过mqtt协议的小伙伴都知道，mqtt主要分为代理服务器、发布者、订阅者三部分。接下来通过mqtt发布者和订阅者两个demo了解mosquitto库函数的使用。
一、Mosquitto库函数的APImosquitto的api说明文档：https://mosquitto.org/api/files/mosquitto-h.html
mosquitto库中常见的函数应用总结：https://blog.csdn.net/makunIT/article/details/107283260
上面这位博主总结的比较好，我就在这里引用一下，需要的小伙伴可以看看。
mqtt_pub_demo.c
#include <stdio.h> #include <stdlib.h> #include <mosquitto.h> #include <string.h> #define HOST "192.168.2.99" #define PORT 1883 #define KEEP_ALIVE 60 #define MSG_MAX_SIZE 512 bool session = true; int main(void) { int err = 0; printf("mqtt publish init...\n"); struct mosquitto *mosq = NULL; char buff[MSG_MAX_SIZE]; //libmosquitto 库初始化 err = mosquitto_lib_init(); if (err < 0){ printf("mosquitto lib int fail..."); goto fail_mosquitto_lib; } //创建mosquitto客户端 mosq = mosquitto_new(NULL,session,NULL); if (mosq == NULL){ printf("create client failed...\n"); err = -1; goto fail_mosquitto_new; } //客户端连接服务器 err = mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE); if (err < 0){ printf("connect fail"); goto fail_mosq_conn; } //不阻塞，库函数中将自动创建线程实现 err = mosquitto_loop_start(mosq); if(err != MOSQ_ERR_SUCCESS){ printf("mosquitto loop error\n"); goto fail_mosq_loop_start; } while(fgets(buff, MSG_MAX_SIZE, stdin) != NULL) { mosquitto_publish(mosq, NULL, "temp", strlen(buff)+1, buff, 0, 0); memset(buff, 0, sizeof(buff)); } mosquitto_disconnect(mosq); mosquitto_loop_stop(mosq, true); mosquitto_destroy(mosq); mosquitto_lib_cleanup(); return 0; fail_mosq_loop_start: mosquitto_disconnect(mosq); fail_mosq_conn: mosquitto_destroy(mosq); fail_mosquitto_new: mosquitto_lib_cleanup(); fail_mosquitto_lib: return err; }Makefile
INCLUDES = -lmosquitto -lpthread -ldl -lssl -lcrypto \ -I/home/linux/arm-lib/mosquitto/include \ -L/home/linux/arm-lib/mosquitto/lib \ -L/homelinux/arm-lib/openssl/lib SOURCE = $(wildcard ./*.c) OBJ = $(patsubst ./%.c, ./%.0, $(SOURCE)) #INCLUDES = $(wildcard ./*.h) TARGET = mqtt_pub_demo CC = arm-linux-gnueabihf-gcc $(TARGET):$(OBJ) $(CC) $(OBJ) -o $(TARGET) $(INCLUDES) %.0:%.c $(CC) -c $< -o $@ $(INCLUDES) clean: rm -rf $(OBJ) $(TARGET) 三、mqtt订阅者源码mqtt_sub_demo.c
#include <stdio.h> #include <stdlib.h> #include <mosquitto.h> #include <string.h> #define HOST "192.168.2.99" #define PORT 1883 #define KEEP_ALIVE 60 bool session = true; void mqtt_subscribe_callback(struct mosquitto *mosq, void *userdata, int mid, int qos_count, const int *granted_qos) { int i; printf("subscribed (mid: %d): %d", mid, granted_qos[0]); for(i=1; i < qos_count; i++){ printf(", %d", granted_qos[i]); } printf("\n"); } //消息回调函数，收到订阅的消息后调用 void mqtt_message_callback(struct mosquitto *mosq, void *userdata, const struct mosquitto_message *message) { if (message->payloadlen){ printf("%s %s \n", message->topic, (char *)message->payload); }else{ printf("%s (null)\n",message->topic); } } //mqtt连接回调 void mqtt_connect_callback(struct mosquitto *mosq, void *userdata, int result) { int ret; if (!result){ ret = mosquitto_subscribe(mosq, NULL, "temp", 2); if(ret < 0){ printf("Subscription failed\n"); }else{ printf("Subscription succeeded\n"); } }else{ printf("connect failed\n"); } } //日志回调函数 void mqtt_log_callback(struct mosquitto *mosq, void *userdata, int level, const char *str) { printf("log__ %s\n", str); } int main(void) { int err = 0; printf("mqtt client init...\n"); struct mosquitto *mosq = NULL; //libmosquitto 库初始化 err = mosquitto_lib_init(); if (err < 0){ printf("mosquitto lib int fail..."); goto fail_mosquitto_lib; } //创建mosquitto客户端 mosq = mosquitto_new(NULL,session,NULL); if (mosq == NULL){ printf("create client failed...\n"); err = -1; goto fail_mosquitto_new; } //设置回调函数 mosquitto_log_callback_set(mosq, mqtt_log_callback); mosquitto_connect_callback_set(mosq, mqtt_connect_callback); mosquitto_message_callback_set(mosq, mqtt_message_callback); mosquitto_subscribe_callback_set(mosq, mqtt_subscribe_callback); //客户端连接服务器 err = mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE); if (err < 0){ printf("connect fail"); goto fail_mosq_conn; } //主线成将被阻塞至此 err = mosquitto_loop_forever(mosq, -1, 1); if (err < 0){ printf("mosquitto loop fail"); goto fail_mosq_loop_stop; } mosquitto_disconnect(mosq); mosquitto_loop_stop(mosq, false); mosquitto_destroy(mosq); mosquitto_lib_cleanup(); return 0; fail_mosq_loop_stop: mosquitto_disconnect(mosq); fail_mosq_conn: mosquitto_destroy(mosq); fail_mosquitto_new: mosquitto_lib_cleanup(); fail_mosquitto_lib: return err; }