In this given C code for JSON parsing, we have implemented functions to handle various types of atoms in a JSON structure. The main steps are as follows:
1. `json_free_value()` – Frees memory allocated for a single value object during error handling or when an unexpected format is encountered.
2. `is_eof(…)` – Checks if the current position of the parser indicates end-of-file (no more characters to parse).
3. `json->advance(…)` – Advances the JSON parser’s internal pointer by one character, moving it forward in the input stream.
4. **Parsing Numbers:** The function `parse_number()` handles integer and floating point numbers using a combination of checks for leading signs (+/-), digits (0-9) followed by optional decimal points and exponents if applicable. It returns an appropriate struct representing the parsed number value.
5. **Parsing Strings:** Function `string(…)` reads characters until encountering double quotes (“”) to form a string atom, escaping any special characters as needed according to JSON syntax rules (e.g., replacing “\n” with actual newline character). It returns a pointer to the resulting string value stored outside of this function’s scope due to memory allocation reasons.
6. **Parsing Boolean:** The `parse_boolean()` function checks for either “true”, “false”, “+null” (for null), or any other invalid input, returning corresponding boolean values or triggering an error if needed.
7. **Parsing Null:** Function `json_value_null(…)` simply creates and returns a struct representing the JSONNull type without doing anything else since it’s just one atom with no further parsing required.
8. **Parsing Objects:** The function `object()` handles objects by checking for valid object start (‘{‘), reading key-value pairs until encountering an end object marker (‘}’). It creates a JSONObject struct, allocates memory for keys and values arrays, popululates them with parsed strings (keys) and corresponding values obtained recursively from calling the parse function again. Finally, it returns this constructed JSONObject instance after advancing past the closing ‘}’ character.
9. **Parsing Arrays:** Similar to objects but instead of key-value pairs, `array()` handles array elements separated by commas (‘,’) within square brackets (‘[‘,’]’). It creates a JSONArray struct with an initial capacity of one element and recursively adds parsed values until reaching either end array marker or EOF condition.
10. **Top Level Parsing:** The `parse()` function serves as the entry point for parsing entire input streams into corresponding JSON structures based on its first character(s). It calls appropriate sub-functions depending upon whether it encounters a number, string, boolean value, null object or array structure respectively before returning the root parsed JSONValue instance.
Note: This explanation assumes familiarity with basic C programming concepts such as structs (data structures), pointers and memory management techniques like `malloc()`, `realloc()` & `free()`. Additionally, it simplifies some aspects of handling escape sequences within strings for brevity purposes but they are handled correctly in the original code provided.
In summary, this C implementation provides a basic JSON parser capable of reading numbers (integer and floating point), strings (including escaped characters), booleans (‘true’, ‘false’ or null) as well as nested arrays and objects conforming to standard JSON syntax rules.
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