I am new to the C language. I need to append two json_object
arrays created with the json-c
library. This is my code:
struct json_object *obj1,*array1,*array2,*array3;
obj1 = json_object_new_object();
array1 = json_object_new_array();
json_object_array_add(array1, json_object_new_int(1));
json_object_array_add(array1, json_object_new_int(2));
json_object_array_add(array1, json_object_new_int(3));
json_object_object_add(obj1, "array1", array1);
array2 = json_object_new_array();
json_object_array_add(array2, json_object_new_int(4));
json_object_array_add(array2, json_object_new_int(5));
json_object_array_add(array2, json_object_new_int(6));
json_object_object_add(obj1, "array2", array2);
json_object_object_add(obj1, "array3", array1+array2);
But I got the following error:
error: invalid operands to binary + (have ‘struct json_object *’ and ‘struct json_object *’) json_object_object_add(obj1, "array3", array1+array2);
Is this not possible? I need output like this:
{
"array1:[1,2,3],
"array2":[4,5,6],
"array3":[1,2,3,4,5,6]
}
Or is it possible to add a normal C integer array to Json, like this
int32_t smp[100]={0};
smp[0] = 1;
smp[1] = 2;
smp[2] = 3;
smp[3] = 4;
smp[4] = 5;
smp[5] = 6;
json_object_object_add(obj1, "array3", smp);
As far as I know, there is no "built-in" function in json-c
to concatenate two arrays, but you can easily create one:
struct json_object * json_object_array_concat (struct json_object *array1,
struct json_object *array2) {
struct json_object *array3 = json_object_new_array();
if (!array3) {
return NULL;
}
int i,
size1 = json_object_array_length(array1),
size2 = json_object_array_length(array2);
for (i = 0; i < size1; ++i) {
json_object_array_add(array3, json_object_array_get_idx(array1, i));
}
for (i = 0; i < size2; ++i) {
json_object_array_add(array3, json_object_array_get_idx(array2, i));
}
return array3;
}
Then to use it:
array3 = json_object_array_concat(array1, array2);
If you only want to append array2
to array1
:
struct json_object * json_object_array_append (struct json_object *array1,
struct json_object *array2) {
int i,
size2 = json_object_array_length(array2);
for (i = 0; i < size2; ++i) {
json_object_array_add(array1, json_object_array_get_idx(array2, i));
}
return array1;
}
Just remember that above answers do not address the reference counts in json-c. They add the objects to the destination array, but do not have it take ownership of them. They will likely cause segfaults etc.
The doc: "The reference count will not be incremented."
To ensure that ownership is held by both arrays, you need something like this:
void json_object_array_append(json_object *dest, json_object *src) {
int i;
int src_size = json_object_array_length(src);
for (i = 0; i < src_size; ++i) {
json_object *src_item = json_object_array_get_idx(src, i);
json_object_get(src_item); // increment reference count
json_object_array_add(dest, src_item); // add to dest array
}
}
// optional: if you are disposing of the src array, you can then do this:
json_object_put(src);
// after calling the append function.
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