Create array and object in a loop - C - arrays

Question

I'm following this tutorial and library on how to work with JSON in C.
https://linuxprograms.wordpress.com/2010/08/19/json_object_new_object/
I have to work on already developed code, so I cannot change library etc..
here's the code I need to devel; basically I need to create a JSON file with different varName, and fill it with arrays ( each varName has it own array ):
#include <json/json.h>
#include <stdio.h>
int main() {
/*Creating a json object*/
json_object *jobj = json_object_new_object();
/*Creating a json array*/
json_object *jarray = json_object_new_array();
json_object *jarray2 = json_object_new_array();
/*Creating json strings*/
json_object *jstring1 = json_object_new_string("10");
int j = 0;
char num[5];
char num2[5];
for (j = 0; j < 3; j++) {
sprintf(num, "%d", j);
printf("num % s\n", num);
jstring1 = json_object_new_string(num);
json_object_array_add(jarray, jstring1);
sprintf(num2, "%d", j + 50);
printf("num2 % s\n", num2);
jstring1 = json_object_new_string(num2);
json_object_array_add(jarray2, jstring1);
}
/*Form the json object*/
char *varName[] = { "categories", "stories" };
/*what if I have N i.e. 1000 varName element ???
how to put this in a loop
varName[i], could have different values */
json_object_object_add(jobj, varName[0], jarray);
json_object_object_add(jobj, varName[1], jarray2);
...
//json_object_object_add(jobj, varName[N], jarrayN); ?? how to do this in a loop ??
/*Now printing the json object*/
printf("The json object created: %s\n", json_object_to_json_string(jobj));
}
this print:
The json object created: { "categories": [ "0", "1", "2" ], "stories": [ "50", "51", "52" ] }
Which is fine, but how to do this in a loop statement?
I could have many varName elements, and each element has an individual array with different values.
Of course I cannot create N *jarray1 to *jarrayN and to the same with , because I do not know N from the beginning.
json_object_object_add(jobj, varName[0], jarray);
json_object_object_add(jobj, varName[N], jarrayN);
Hope my question is clear

Answer 1

Are you maybe looking for something like this?
#include <json-c/json.h>
#include <stdio.h>
#include <string.h>
static json_object *build_array(const char *var_name) {
printf("Building array for %s...\n", var_name);
json_object *array = json_object_new_array();
for (int j = 0; j < strlen(var_name); j++) {
char num[8];
sprintf(num, "%d", j);
json_object_array_add(array, json_object_new_string(num));
}
return array;
}
int main() {
json_object *root_obj = json_object_new_object();
// since we might not know the length of this array beforehand,
// a NULL string shall denote the last element.
char *var_names[] = {"categories", "stories", "cats", "dogs", NULL};
for (char **var_name_ptr = var_names; *var_name_ptr; var_name_ptr++) {
char *var_name = *var_name_ptr;
json_object *array = build_array(var_name);
json_object_object_add(root_obj, var_name, array);
}
printf("The json object created: %s\n", json_object_to_json_string(root_obj));
json_object_put(root_obj); // Release the root object
}
The output is
Building array for categories...
Building array for stories...
Building array for cats...
Building array for dogs...
The json object created: { "categories": [ "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" ], "stories": [ "0", "1", "2", "3", "4", "5", "6" ], "cats": [ "0", "1", "2", "3" ], "dogs": [ "0", "1", "2", "3" ] }