Buffer JSON data and publish through MQTT nrf9160

Question

Hi Dev Team, 
 I have an application wherein I am publishing my sensor data every hour through MQTT using a Thingy91. 
 I am storing my sensor data value in a JSON format through cJSON library. I need to read this value every 10 mins, buffer it and send out all the values every hour. 
 So basically I need to store 6 values (values obtained every 10 mins through the hour) and send them out together every 1 hour. 
 I needed to know how could I buffer my sensor data and store it to send all of it together every hour. 
 I obtain my JSON format through this following code: 
 void my_work_handler_1(struct k_work *work)
{

 char *desc2 = "BME680";
 char *id2 = "rH";
 char *type2 = "humidity";

 sensor1 = cJSON_CreateObject();

 cJSON_AddItemToObject(sensor1, "description", cJSON_CreateString(desc2));
 cJSON_AddItemToObject(sensor1, "Time", cJSON_CreateString(time_string));
 cJSON_AddItemToObject(sensor1, "value", cJSON_CreateNumber(testval2));
 cJSON_AddItemToObject(sensor1, "unit", cJSON_CreateString(id2));
 cJSON_AddItemToObject(sensor1, "type", cJSON_CreateString(type2));

 /* print everything */
 out1 = cJSON_Print(sensor1);
 printk("%s
", out1);
 free(out1);
 /* free all objects under root and root itself */
 cJSON_Delete(sensor1);
 return;

}
K_WORK_DEFINE(my_work1, my_work_handler_1);
 
 I save my json in the variable "out1" in the code. I wanted to know how I could buffer the output and store it in a variable, so I could publish that through MQTT every hour. 
 Regards, 
 Adeel.

Didrik Rokhaug · Accepted Answer

You need to free sensor6 each time my_work_handler_6 runs, otherwise you will leak the memory allocated by cJSON_CreateObject(). 
 If you move the call to cJSON_Delete() out of the for loop

Didrik Rokhaug · Answer

Adeel said: What can be the maximum value of these configurations ? and how do they effect the memory ? 
 You are obviously limited by the amount of RAM in the system. 
 CONFIG_MAIN_STACK_SIZE sets the stack size for the main thread, but there are often other threads as well. The sum of all the stack sizes, and the heap size should not be more than the amount of RAM in the system. 
 However, you might be able to set higher numbers, as long as you don't use too much RAM. If a stack or the heap starts to grow into a different area, weird things can happen (but porbably you just get a crash. Regardless, don't do that). 
 When it comes to the heap, the memory allocation algorithm will also be a consideration. Depending on the algorithm, increasing the heap size might not let you allocate more items, just bigger items.

Buffer JSON data and publish through MQTT nrf9160

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