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title: facil.io - JSON support toc: true layout: api

Using facil.io's JSON support

Parsing, editing and outputting JSON in C can be easily accomplished using facil.io's dynamic types (fiobj_s).

There are faster alternatives as well as slower alternatives out there (i.e., the Qajson4c library is probably the most balanced alternative).

However, facil.io offers the added benefit of complete parsing from JSON to object. This is in contrast to some parsers that offer a mid-way structure (often a linked list of JSON nodes) or lazy (delayed) parsing for types such as true, false and Numbers.

facil.io also offers the added benefit of complete formatting from a framework wide object type (FIOBJ) to JSON. This is in contrast to some solutions that require a linked list of node structures.

Parsing JSON

The facil.io parser will parse any C string until it either consumes the whole string or completes parsing of a JSON object.

For example, the following program will minify (or prettify) JSON data:

// include the `fiobj` module from `facil.io`
#include "fiobj.h"
#include <string.h>
// this is passed as an argument to `fiobj_obj2json`
// change this to 1 to prettify.
#define PRETTY 0

int main(int argc, char const *argv[]) {
  // a default string to demo
  const char * json = u8"{\n\t\"id\":1,\n"
                     "\t// comments are ignored.\n"
                     "\t\"number\":42,\n"
                     "\t\"float\":42.42,\n"
                     "\t\"string\":\"𝄞 oh yeah...\",\n"
                     "\t\"hash\":{\n"
                     "\t\t\"nested\":true\n"
                     "\t},\n"
                     "\t\"symbols\":[\"id\","
                     "\"number\",\"float\",\"string\",\"hash\",\"symbols\"]\n}";
  if (argc == 2) {
    // accept command line JSON data
    json = argv[1];
  }
  printf("\nattempting to parse:\n%s\n", json);
  // actual code for parsing the JSON
  FIOBJ obj;
  size_t consumed = fiobj_json2obj(&obj, json, strlen(json));
  // test for errors
  if (!obj) {
    printf("\nERROR, couldn't parse data.\n");
    exit(-1);
  }
  // format the JSON back to a String object and print it up
  FIOBJ str = fiobj_obj2json(obj, PRETTY);
  printf("\nParsed JSON input was: %lu bytes"
         "\nJSON output is %lu bytes:\n\n%s\n\n",
         consumed, (size_t)fiobj_obj2cstr(str).len, fiobj_obj2cstr(str).data);
  // cleanup
  fiobj_free(str);
  fiobj_free(obj);
  return 0;
}