C JSON Parser

Just a simple project to practice writing parsers. Not guaranteed to be safe, reliable or efficient.

Usage

Compile

build (release build):

make BUILD=release

To make a debug build just run make.

Run

./bin/release/json_parser  sample-files/large-file.json

Implementation

Parsed JSON values are stored as structs containing type information and data.

enum json_type { object, array, string, number, boolean, null };

struct json_value {
    enum json_type type;

    union {
        obj_t*              object;
        struct json_value** array;
        char*               string;
        bool                boolean;
        double              number;
    };
};

Types

JSON Objects

Object values have the type field set to (enum json_type) object

They are stored using a poorly written map implementation with the type obj_t in json_value.object

See obj_t for more details.

JSON Arrays

Array values have the type field set to (enum json_type) array

JSON Arrays are stored as null-terminated json_value* arrays, i.e. struct json_value**, in json_value.array

JSON Numbers

Number values have the type field set to (enum json_type) number

Numbers are stored as double values in json_value.number

(The JSON specification doesn't strictly specify a maximum value, but double is sufficient for parsing almost all JSON data.)

JSON Strings

Strings have the type field set to (enum json_type) string

Strings are stored as null-terminated char arrays, char*, in json_value.string

JSON Booleans

Boolean values have the type field set to (enum json_type) boolean

The values are stored as bool in json_value.boolean

JSON Null

Null values have type field set to (enum json_type) null.

obj_t

obj_t is defined in json_value.h as:

typedef struct obj_entry {
    char const* key;
    struct json_value* val;
    struct obj_entry* next;
} * __p_obj_entry;

typedef __p_obj_entry obj_t[OBJ_SIZE]; // OBJ_SIZE=1024

obj_t methods

void* obj_at(obj_t m, char* key)

Returns a pointer to a value for the given key.

bool obj_insert(obj_t m, char* const key, struct json_value* value)

Insert a key-value pair

void obj_delete(obj_t m)

Recursively free memory allocated for object and children objects.