JSON Parser Library in C

This library provides a simple API for parsing, constructing, and manipulating JSON data in C. It uses an opaque data type (json_value) for JSON values and exposes functions to parse a JSON string into an internal representation, create new JSON objects or arrays programmatically, access their elements, and free the allocated memory.

Features

• Parsing: Convert a JSON-formatted string into a tree of JSON values.
• Construction: Create JSON values such as objects, arrays, strings, numbers, booleans, and null.
• Accessors: Retrieve values from objects and arrays using simple APIs.
• Error Handling: Retrieve human-readable error messages when operations fail.
• Memory Management: Automatically allocate and free all memory associated with JSON values.

Importing the Library

To use this library in your project, simply include the header file in your source code. For example, add the following line at the top of your C file:

#include "jsonparser.h"

Then, compile your project along with all of the library’s source files. For example, if you are using GCC and the library files (jsonparser.c and jsontokenizer.c) are in the same directory as your source file, compile with:

gcc -o your_app your_app.c jsonparser.c jsontokenizer.c -I.

Make sure to adjust the include path (-I) if your header files are in a different directory.

Installation

The library uses a simple Makefile for building the project. To compile the library and tests, run:

make

This command builds an executable named tests that runs a comprehensive suite of tests against the parser.

API Overview

Parsing

• json_value *json_parse(const char *json_text);
  Parses a JSON string and returns a pointer to a JSON value tree. Returns NULL if parsing fails.
  
  Example

  const char *json_text = "{\"name\": \"Alice\", \"age\": 30}";
  json_value *root = json_parse(json_text);
  if (!root) {
    fprintf(stderr, "Error: %s\n", json_get_last_error());
  }

Serialization

• char *json_serialize(const json_value *value);
  [Not yet implemented] Serializes a JSON value into a string. The caller is responsible for freeing the returned string.

Memory Management

• void json_free(json_value *value);
  Frees a JSON value and all its children.

Creating JSON Values

• json_value *json_new_null(void);
  Creates a JSON null value.
• json_value *json_new_boolean(int boolean);
  Creates a JSON boolean value.
• json_value *json_new_number(double number);
  Creates a JSON number value.
• json_value *json_new_string(const char *string);
  Creates a JSON string value. Note: Passing NULL returns NULL.
• json_value *json_new_array(void);
  Creates an empty JSON array.
• json_value *json_new_object(void);
  Creates an empty JSON object.

Object and array manipulation

• int json_object_set(json_value *object, const char *key, json_value *value);
  Adds or updates a key-value pair in a JSON object.
  Example:

  json_value *obj = json_new_object();
  json_object_set(obj, "name", json_new_string("Bob"));

• json_value *json_object_get(const json_value *object, const char *key);
  Retrieves the JSON value associated with a key in an object.
• int json_array_append(json_value *array, json_value *value);
  Appends a value to a JSON array.
• json_value *json_array_get(const json_value *array, size_t index);
  Retrieves the element at the specified index in a JSON array.

Accessors for JSON Value Types

• int json_get_type(const json_value *v);
  Returns the type of the JSON value (e.g., JSON_STRING, JSON_NUMBER).
• char *json_get_string(const json_value *v);
  Returns the C string if the JSON value is a string.
• double json_get_number(const json_value *v);
  Returns the number if the JSON value is a number.
• uint8_t json_get_boolean(const json_value *v);
  Returns the boolean value if the JSON value is a boolean.

Error handling

• const char *json_get_last_error(void); Returns the last error message recorded by the library. This is useful for debugging when an API call fails.

if (!json_parse(some_bad_json)) {
    fprintf(stderr, "Parsing error: %s\n", json_get_last_error());
}

Example usage

#include <stdio.h>
#include "jsonparser.h"

int main(void) {
    const char *json_text = "{\"name\": \"Alice\", \"age\": 30, \"hobbies\": [\"reading\", \"coding\"]}";
    json_value *root = json_parse(json_text);
    
    if (!root) {
        fprintf(stderr, "Failed to parse JSON: %s\n", json_get_last_error());
        return 1;
    }
    
    json_value *name = json_object_get(root, "name");
    if (name && json_get_type(name) == JSON_STRING) {
        printf("Name: %s\n", json_get_string(name));
    }
    
    // Clean up memory
    json_free(root);
    return 0;
}

Running tests

To run the test suite, execute:

./tests

This will run both the basic tests and the extended tests (if present) that cover complex, deeply nested, and invalid JSON scenarios.

Contributing

Feel free to fork the repository and submit pull requests. Improvements in error handling, serialization, or performance are welcome.