On every even index, i need to send the constructed json over MQTT and have to clear the json once it is sent and have to construct the json again and for the same, I am using the below script,
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#include <jansson.h>
char *jsonString;
void sendMQTT(char *jsonString){
MQTTClient client;
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
MQTTClient_message pubmsg = MQTTClient_message_initializer;
MQTTClient_deliveryToken token;
int rc;
MQTTClient_create(&client, "tcp://localhost:1883", "client-pub",
MQTTCLIENT_PERSISTENCE_NONE, NULL);
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to connect, return code %d\n", rc);
exit(EXIT_FAILURE);
}
printf("Inside MQTT :: %s\n", jsonString);
pubmsg.payload = jsonString;
pubmsg.payloadlen = (int)strlen(jsonString);
pubmsg.qos = 1;
pubmsg.retained = 0;
MQTTClient_publishMessage(client, "mqtt-ex", &pubmsg, &token);
rc = MQTTClient_waitForCompletion(client, token, 10000L);
MQTTClient_disconnect(client, 10000);
MQTTClient_destroy(&client);
}
int main() {
json_t *root = json_object();
char myNum[10] = {10, 20, 10, 40, 10, 60, 10, 80, 10, 100};
for(int i=0; i<10;i++)
{
int json_size = json_object_size(root);
printf("json_size %d\n", json_size);
if(i%2==0 && json_size !=0)
{
sendMQTT(jsonString);
free(jsonString);
json_decref(root);
json_t *root = json_object();
}
char *key= (char*)malloc(8);
snprintf(key, sizeof(key), "%d", myNum[i]);
json_object_set_new( root, key, json_integer(i));
char *jsonString= (char*)malloc(100);
jsonString = json_dumps(root, 0);
printf("json_string :!!: %s\n", jsonString);
free(key);
}
}
Whereas, when I compile and execute the same,
gdb ./editing_file
GNU gdb (Ubuntu 8.2-0ubuntu1~18.04) 8.2
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./editing_file...done.
(gdb) run
Starting program: /home/sam/workspace_folder/sample/editing_file
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
json_size 0
json_string :!!: {"10": 0}
json_size 1
json_string :!!: {"10": 0, "20": 1}
json_size 2
Inside MQTT :: (null)
Program received signal SIGSEGV, Segmentation fault.
__strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:62
62 ../sysdeps/x86_64/multiarch/strlen-avx2.S: No such file or directory.
(gdb) where
#0 __strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:62
#1 0x0000555555554f61 in sendMQTT (jsonString=0x0) at editing_file.c:29
#2 0x0000555555555093 in main () at editing_file.c:51
(gdb)
How to resolve this? What is wrong in this above process and how to rectify this?
Suggestions from comments
After the suggestion from the comments, the above code has been modified as,
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
#include <jansson.h>
char *jsonString;
void sendMQTT(char *jsonString){
MQTTClient client;
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
MQTTClient_message pubmsg = MQTTClient_message_initializer;
MQTTClient_deliveryToken token;
int rc;
MQTTClient_create(&client, "tcp://localhost:1883", "client-pub",
MQTTCLIENT_PERSISTENCE_NONE, NULL);
conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;
if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
{
printf("Failed to connect, return code %d\n", rc);
exit(EXIT_FAILURE);
}
printf("Inside MQTT :: %s\n", jsonString);
pubmsg.payload = jsonString;
pubmsg.payloadlen = (int)strlen(jsonString);
pubmsg.qos = 1;
pubmsg.retained = 0;
MQTTClient_publishMessage(client, "mqtt-ex", &pubmsg, &token);
rc = MQTTClient_waitForCompletion(client, token, 10000L);
MQTTClient_disconnect(client, 10000);
MQTTClient_destroy(&client);
}
int main() {
json_t *root = json_object();
char myNum[10] = {10, 20, 10, 40, 10, 60, 10, 80, 10, 100};
for(int i=0; i<10;i++)
{
int json_size = json_object_size(root);
if(i%2==0 && json_size !=0)
{
sendMQTT(jsonString);
json_object_clear(root);
jsonString = json_dumps(root, 0);
printf("Inside for ===%s\n", jsonString);
}
char *key= (char*)malloc(8);
snprintf(key, sizeof(key), "%d", myNum[i]);
json_object_set_new( root, key, json_integer(i));
jsonString = json_dumps(root, 0);
}
}
and able to achieve the desired result i.e.,
gdb ./editing_file
GNU gdb (Ubuntu 8.2-0ubuntu1~18.04) 8.2
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./editing_file...done.
(gdb) run
Starting program: /home/sam/workspace_folder/sample/editing_file [Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Inside MQTT :: {"10": 0, "20": 1}
Inside for ==={}
Inside MQTT :: {"10": 2, "40": 3}
Inside for ==={}
Inside MQTT :: {"10": 4, "60": 5}
Inside for ==={}
Inside MQTT :: {"10": 6, "80": 7}
Inside for ==={}
[Inferior 1 (process 20590) exited normally]
