JSML is a lightweight C library for parsing and manipulating JSON data.
- Parse JSON data from a string or a file.
- Access JSON values by key or index.
- Helper functions for accessing nested JSON values and printing JSON data (along with datatypes).
- Free up memory used by JSON data.
All you need to do is include the jsml.h header file in your project.
#include "jsml.h"Note: The unescape_json_string_literal function is only needed if you are parsing a JSON string that is hardcoded and escaped. If you are parsing a JSON string, you can skip this step.
char* json_string = "{\"key\": \"value\"}";
const json* parsed_json = json_parse_utf8(unescape_json_string_literal(json_string));
if (parsed_json) {
json_print(parsed_json, 0);
}
json_free(parsed_json);const json* parsed_json_file = json_parse_file_utf8("example.json");
if (parsed_json_file) {
json_print(parsed_json_file, 0);
}
json_free(parsed_json_file);You can access JSON values by key or index using the json_get and json_item functions. Here is an example:
For this example, we will use the following JSON data:
{
"int": 195,
"array": [3, 5.1, -7, "nine"],
"bool": true,
"double": -1e-4,
"null-value": null,
"hello": "world!",
"obj": {
"key": "val",
"double": 1e4
},
"nested": [
{
"a": "b"
},
{
"a": 69
},
{
"a": [4, 2, 0]
}
]
}NOTE: Please assert that the value returned by json_get or json_item is not NULL before accessing the value. For the sake of brevity, we have omitted the assertions in the following examples.
const json* parsed_json = json_parse_file_utf8("example.json");
/* Access values */
const json *int_node = json_get(parsed_json, "int");
assert(int_node->type == JSON_INTEGER);
printf("int: %lld\n", int_node->json_integer);
printf("bool: %s\n",
json_get(parsed_json, "bool")->json_bool ? "true" : "false");
printf("double: %f\n", json_get(parsed_json, "double")->json_double);
printf("some-null: %s\n",
json_get(parsed_json, "null-value")->type == JSON_NULL ? "null"
: "not null");
printf("hello: %s\n", json_get(parsed_json, "hello")->json_string);
printf("obj.key: %s\n",
json_get(json_get(parsed_json, "obj"), "key")->json_string);
printf("obj.double: %f\n\n",
json_get(json_get(parsed_json, "obj"), "double")->json_double);
/* Nested */
printf("nested[0].a: %s\n",
json_get(json_item(json_get(parsed_json, "nested"), 0), "a")
->json_string);
printf("nested[1].a: %lld\n",
json_get(json_item(json_get(parsed_json, "nested"), 1), "a")
->json_integer);
printf("nested[2].a[0]: %lld\n",
json_item(
json_get(json_item(json_get(parsed_json, "nested"), 2), "a"), 0)
->json_integer);
printf("nested[2].a[1]: %lld\n",
json_item(
json_get(json_item(json_get(parsed_json, "nested"), 2), "a"), 1)
->json_integer);
printf("nested[2].a[2]: %lld\n\n",
json_item(
json_get(json_item(json_get(parsed_json, "nested"), 2), "a"), 2)
->json_integer);
/* Nested helper */
printf("(Helper) obj.key: %s\n",
json_get_nested(parsed_json, "obj.key")->json_string);
printf("(Helper) obj.double: %f\n",
json_get_nested(parsed_json, "obj.double")->json_double);
printf("--------------------\n\n");
json_free(parsed_json_file);Output
int: 195
bool: true
double: -0.000100
some-null: null
hello: world!
obj.key: val
obj.double: 10000.000000
nested[0].a: b
nested[1].a: 69
nested[2].a[0]: 4
nested[2].a[1]: 2
nested[2].a[2]: 0
(Helper) obj.key: val
(Helper) obj.double: 10000.000000
--------------------
Array Example
// access array
const json *array = json_get(parsed_json, "array");
assert(array->type == JSON_ARRAY);
// access array elements
for (size_t i = 0; i < array->length; i++) {
const json *element = json_item(array, i);
switch (element->type) {
case JSON_INTEGER:
printf("array[%zu]: %lld (int)\n", i, element->json_integer);
break;
case JSON_DOUBLE:
printf("array[%zu]: %f (double)\n", i, element->json_double);
break;
case JSON_STRING:
printf("array[%zu]: %s (string)\n", i, element->json_string);
break;
case JSON_BOOL:
printf("array[%zu]: %s (bool)\n", i,
element->json_bool ? "true" : "false");
break;
case JSON_NULL:
printf("array[%zu]: null (NULL)\n", i);
break;
default:
break;
}
}Output
array[0]: 3 (int)
array[1]: 5.100000 (double)
array[2]: -7 (int)
array[3]: nine (string)
You can print JSON data using the json_print function. Here is an example:
if (parsed_json) {
json_print(parsed_json);
}Output
┼── int: 195 (int)
┼── array: ARRAY
┼──┼── 3 (int)
┼──┼── 5.100000 (double)
┼──┼── -7 (int)
┼──┼── nine (string)
┼── bool: true (bool)
┼── double: -0.000100 (double)
┼── null-value: NULL
┼── hello: world! (string)
┼── obj: OBJECT
┼──┼── key: val (string)
┼──┼── double: 10000.000000 (double)
┼── nested: ARRAY
┼──┼── OBJECT
┼──┼──┼── a: b (string)
┼──┼── OBJECT
┼──┼──┼── a: 69 (int)
┼──┼── OBJECT
┼──┼──┼── a: ARRAY
┼──┼──┼──┼── 4 (int)
┼──┼──┼──┼── 2 (int)
┼──┼──┼──┼── 0 (int)
You can free up memory used by JSON data using the json_free function. Here is an example:
/* PLEASE FREE TO AVOID MEMORY LEAKS */
json_free(parsed_json_file);
json_free(parsed_json);For more details, please refer to the jsml.h header file.
typedef enum json_type {
JSON_NULL,
JSON_OBJECT,
JSON_ARRAY,
JSON_STRING,
JSON_INTEGER,
JSON_DOUBLE,
JSON_BOOL
} json_type;
typedef struct json {
json_type type; // type of json node, based on json_type enum
const char *key; // key of the property; applicable only for OBJECT
const char *json_string; // value of STRING node
long long json_integer; // value of INTEGER node
int json_bool; // value of BOOL node
double json_double; // value of DOUBLE node
int length; // number of children of OBJECT or ARRAY
struct json *child; // points to first child
struct json *next; // points to next child
struct json *last_child;
} json;
typedef int (*json_unicode_encoder)(unsigned int codepoint, char *p,
char **endp);
/* String Parse Functions */
const json *json_parse(char *text, json_unicode_encoder encoder);
const json *json_parse_file(char *file_path, json_unicode_encoder encoder);
/* File Parse Functions */
const json *json_parse_utf8(char *text);
const json *json_parse_file_utf8(char *file_path);
/* JSON Access Functions */
const json *json_get(const json *json,
const char *key); // get object's property by key
const json *json_item(const json *json, int idx); // get array element by index
const json *json_get_nested(const json *parsed_json,
const char *key); // get nested object/array
/* Extra Helper Functions */
char *unescape_json_string_literal(const char *str);
void json_print(const json *parsed_json);
void json_recursive_print(const json *parsed_json, int depth);
void json_free(const json *js);You can find examples of how to use this library in the examples directory.
- example.c - Example of parsing JSON from a string literal and a file.
- Usage:
gcc -o example examples/example.c; ./example - api_example.c - Example of using the API functions.
- Usage:
gcc -o api_example examples/api_example.c -lcurl; ./api_example
This project is licensed under the MIT License. See the LICENSE file for details.