array packetizer in JSON format in C - arrays

Question

I am developing the JSON array packetizer in C to send response back to http server
example format in JSON array
"fat": [
23,
152689,
"Segmentation Fault"
]
Code in C
void arrFunc(char* buffer, const char* name, const int* value, int count)
{
if ((buffer == NULL) || (name == NULL))
{
return;
}
char numberChar[VALUE_FIELD_LENGTH];
strncat(buffer, "\"", 1);
strncat(buffer, name, strlen(name));
strncat(buffer, "\":", 2);
strncat(buffer, "[", 1);
if (value != NULL)
{
for (int i = 0; i < count; i++)
- {
snprintf(numberChar, VALUE_FIELD_LENGTH, "%u", value[i]);
strncat(buffer, numberChar, 1);
if(i<count-1)
strncat(buffer, ",", 1);
numberChar[i] = '\0';
}
}
strncat(buffer, "]", 1);
}
/* main *//
int arr[5] = { 1,2,3,4,5 };
char* msg;
if (msg != NULL)
{
msg[0] = '\0';
arrFunc(msg, "fat",(const int *) arr,3);
}
Output :
"fat": [
1,
2,
3
]
I am able to achieve array packetizer of similar data types like integer but how to achive for
different data type [23,152689,"Segmentation Fault"]

Answer 1

There's many ways to solve this problem, but one of them is tagged unions.
#include <stdio.h>
// TODO: include an implementation of a map
struct map {};
// TODO: include a dynamic array that knows size of data it holds
struct array {};
enum DataType {
JSON_MAP,
JSON_ARRAY,
JSON_NUMBER,
JSON_STRING
};
union Data {
float number;
char* string;
struct map map;
struct array array;
};
struct Json {
enum DataType kind;
union Data data;
};
// TODO: turn this into json serializer
void print_json(struct Json data) {
switch(data.kind) {
case JSON_NUMBER:
printf("%d\n", data.data.number);
break;
case JSON_STRING:
puts(data.data.string);
break;
default:
puts("TODO: print map and array");
}
}
int main() {
struct Json data1 = { .kind = JSON_NUMBER, .data.number = 12.34 };
struct Json data2 = { .kind = JSON_STRING, .data.string = "Hello, Json!" };
// invalid, but we never read it in this example
struct Json data3 = { .kind = JSON_ARRAY };
print_json(data1);
print_json(data2);
print_json(data3);
}
I don't think this requires further explanation but keep in mind that both the map and array should hold elements of type struct Json too, which is how you can build structures such as:
{ // JSON_MAP
"example": [ // JSON_ARRAY
1, // JSON_NUMBER
"42", // JSON_STRING
{ "etc": { "1": 2, "a": [3, 2, 1] } } // JSON_MAP (again)
]
}