How to parse json using sscanf in C?

Question

I have the following string in the form of json:

{
   "num":1,
   "data":{
      "city":"delhi"
   }
}

I need to get the value of "num" key using sscanf. Here is my attempt. I know it's incorrect. But I don't know how to do it.

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    
    char *str = "{\"num\":1,\"data\":{\"city\":\"delhi\"}}";
    char *ret = malloc(sizeof(char) * 10);
    
    sscanf(str, "{\"num\":%s, %s" , ret);
    
    printf("%s", ret);
    return 0;
}

Any suggestions?

Answer 1

sscanf(str, "{\"num\":%s, %s" , ret);

is wrong, first you have two "%s" but you give only one location to save string (ret), and it does not extract as you expect

you want

#include <stdio.h>
#include <stdlib.h>

int main(void) {

    char *str = "{\"num\":1,\"data\":{\"city\":\"delhi\"}}";
    char *ret = malloc(10); /* by definition sizeof(char) is 1 */

    if (sscanf(str, "{\"num\":%9[^,]" , ret) == 1)
        printf("value is '%s'\n", ret);

    free(ret);
    return 0;
}

Compilation and execution

/tmp % gcc -Wall p.c
/tmp % ./a.out
value is '1'
/tmp % 

but to use scanf to parse is limited