Back View on GitHub

JSON parser

A zlib licensed json parser written in C, supports wchar_t.


The JSON parser works with both char and wchar_t. It will use wchar_t by default, if you want to use single-byte characters instead you can #define JSON_USE_SINGLE_BYTE json_char is either defined as a char or wchar_t, depending on which to use.

The macro JSTR will append an L to your string if using multibyte and do nothing in single byte. Example:

  1. Multibyte: JSTR("Hello world") -> `L"Hello world"
  2. Single byte: JSTR("Hello world")` -> `"Hello world"


To parse JSON, you have the following options:

json_char* some_text = JSTR("[ 1, 2, 3, 4, 5, null ]");
JsonValue json = json_parse(some_text);

Or if you want to load it from a file

JsonValue json = json_parse_from_file("config.json");

Note that json_parse_from_file() will heap-allocate a string that can hold the value and then call json_parse() on that and free it.


To access the various types that the JsonValue can hold, you can access them in various different ways. There are 6 defined types in the implementation:

  2. JSON_STRING -> JsonValue.string_value (json_char*)
  3. JSON_NUMBER -> JsonValue.number_value (double`)
  4. JSON_OBJECT -> JsonValue.object_value (JsonObject*)
  5. JSON_ARRAY -> JsonValue.array_value (JsonArray*)
  6. JSON_BOOL -> JsonValue.bool_value (bool)

You can get the type of the JsonValue by doing JsonValue.type and comparing it with the enum listed above. Note that all these values are in a union.

For arrays and objects you can use the overloaded subscript operator if using C++:

JsonValue json = json_parse(JSTR("[ 0, 1, 2, 3 ]"));

for (int i = 0; i < json.array_value->count; ++i) {
  JsonValue& val = json[i];
  // OR
  JsonValue& val = json.array_value->values[i];
  // ...

Or with objects:

JsonValue json = json_parse(JSTR("{ \"age\": 41.9 }");

JsonValue& age = json[JSTR("age")];
// OR
JsonValue& age = json_find_field_ref(&json, JSTR("age"));


Creating new JSON values is quite easy. You can call json_*type* to get a JsonValue of that type:

json_char* str = json_string(JSTR("Hello, world!"));
double num = json_number(10.04);

To add elements to an array you can use json_add_element():

JsonValue arr = json_array();
json_add_element(&arr, json_number(10.0));
json_add_element(&arr, json_bool(1));

JsonValue nested_arr = json_array();
json_add_element(&nested_arr, json_string(JSTR("wow")));

json_add_element(&arr, nested_arr);

If you want to remove an element, you can use json_remove_element(&arr, index) Note that it will take care of resizing an array. It only grows. If you add a heap-allocated JsonValue (array/object/string) to a JsonValue it will assume ownership of the pointer.


JsonValue str = json_string(JSTR("DON'T"));

JsonValue arr1 = json_array();
json_add_element(&arr1, str);

JsonValue arr2 = json_array();
json_add_element(&arr2, str);

In the above example, both arrays have assumed ownership over the string. If you were to free 1 and still use the other you'd have a free-after-use error. BEWARE! Consider using json_duplicate() to make copies of a JsonValue.

Adding fields to objects is similar to arrays, you can use json_add_field():

JsonValue obj = json_object();
json_add_field(&obj, JSTR("key"), json_number(10.0));

Note that it will not check if a certain field already exists as per the ECMA-404 standard. More control over seeing if fields exist/removing fields/etc is still @TODO.


To export a JsonValue all you have to do is call json_export():

JsonValue json = ...;
JSON_BOOL_TYPE minified = 1;
json_export(&json, "path/to/file.json", minified);

Stringifying a JsonValue is still @TODO.

Customize your export:

  1. #define JSON_INDENT_CHAR to change the character used for indenting. Space ' ' by default.
  2. #define JSON_INDENT_STEP by how many characters it will indent. 2 is the default.


These settings allow you to customize how the parser behaves. Enabling these settings will make the parser no longer compliant with ECMA-404.

  1. #define JSON_ALLOW_EXP_DECIMALS: Allow floating-point numbers in the number exponent e.g. 10e2.4
  2. #define JSON_ALLOW_COMMENTS: Allows single-line comments using #, will be ignored by the parser.