JSON Parser in C

Quick Start

• Compile tests using:

  $ make test

• Run fmtjson program with command line argument as an unformatted JSON file:

  $ ./fmtjson <FILE>

Usage

• It is assumed that all JSON objects start with the object notation, and doesn't have other types as the parent.

• There are two family of functions concerning object key-value addition or extraction.

  • Addition/Setting key-value pair (KVP):

    void set_value_for_key(struct Object* obj, String key, enum JSONType type, void* value);
    
    void set_int32_t_for_key(struct Object* obj, String key, int x);
    void set_int64_t_for_key(struct Object* obj, String key, int64_t x);
    void set_double_for_key(struct Object* obj, String key, double x);
    void set_char_for_key(struct Object* obj, String key, char x);
    void set_string_for_key(struct Object* obj, String key, String x);
    void set_object_for_key(struct Object* obj, String key, struct Object x);
    void set_array_for_key(struct Object* obj, String key, Array x);
    void set_bool_for_key(struct Object* obj, String key, bool x);
    void set_null_for_key(struct Object* obj, String key);

    • PS: It is be noted that the above functions also allow modification of value for the key

  • Extraction of key-value pair (KVP):

    void* get_value_for_key(struct Object* obj, String key);
    
    // DO NOT USE THESE FUNCTIONS IF NOT SURE ABOUT THE TYPE
    int get_int32_t_for_key(struct Object* obj, String key);
    int64_t get_int64_t_for_key(struct Object* obj, String key);
    double get_double_for_key(struct Object* obj, String key);
    char get_char_for_key(struct Object* obj, String key);
    String* get_string_for_key(struct Object* obj, String key);
    struct Object* get_object_for_key(struct Object* obj, String key);
    Array* get_array_for_key(struct Object* obj, String key);
    bool get_bool_for_key(struct Object* obj, String key);

Loading and Dumping JSON (basically formatting JSON)

• Consider the file unformatted.json:

  {"name":"Dinesh Chukkala","address":{"user":"HumanChwan","host":"github.com","repo":"json-parser"}}

• Compile and run the following code:

  #include "Object.h"
  
  #include <stdio.h>
  
  int main(void) {
      FILE* fp = fopen("unformatted.json", "r");
      struct Object obj = load_json(fp);
      fclose(fp)
  
      fp = fopen("unformatted.json", "w");
      dump_json(fp, obj, 0,     4);
      //                 ^      ^
      //               depth  indent
      fclose(fp);
  }

  $ gcc -o main main.c String.c Object.c Array.c
  $ ./main

• Find the file unformatted.json:

  {
      "name": "Dinesh Chukkala",
      "address": {
          "user": "HumanChwan",
          "host": "github.com",
          "repo": "json-parser"
      }
  }

Creating an Object

• Create an object using the following function:

  struct Object obj = create_object();
  // Present state of object:
  /*
   * {}
   */

• Using the setter function family, new KVP can be added or existing Key's value can be modified.

  • Adding String value for a key:

  set_string_for_key(&obj, IMM_STRING("name"), IMM_STRING("Dinesh Chukkala"));
  // Present state of object:
  /*
   * {
   *     "name": "Dinesh Chukkala"
   * }
   */

  • Adding a nested object:

  struct Object address = create_object();
  
  set_string_for_key(&address, IMM_STRING("repo"), IMM_STRING("json-parser"));
  set_string_for_key(&address, IMM_STRING("user"), IMM_STRING("HumanChwan"));
  set_string_for_key(&address, IMM_STRING("host"), IMM_STRING("github.com"));
  
  set_object_for_key(&obj, IMM_STRING("address"), address);
  // Present state of object:
  /*
   * {
   *     "name": "Dinesh Chukkala",
   *     "address": {
   *         "repo": "json-parser",
   *         "user": "HumanChwan",
   *         "host": "github.com"
   *     }
   * }
   */

• Dump the object into a json file:

  // Open a file with write mode
  FILE* fp = fopen("test.json", "w");
  
  dump_json(dp, obj, 0, 4);