Small Json Parser

This is a small json parser that tries to be compliant with ECMA-404. I wrote this mainly for fun to be able to use json in other C Projects of mine. It has basic features for parsing a json file to use the data. Theres also functionality to create new json files and update existing ones.

important limitations

The maximum length of a string in a parsed json file is 100 000 bits in this implementation. I opted against using a variable length string here to increase performance on large files. This upper limit is set with the MAX_SAFE_STR definition at compile time.

Data structures

Every piece of data in the json file is represented as a value in form of the json_val struct. These structs have a type member and a data member. The data member is a void pointer that can be cast depending on the type:

Type	Data
JSON_NUM	Float
JSON_STR	char*
JSON_LITERAL	integer constant that can be used as a bool
JSON_OBJ	A HashList object (see below)
JSON_LIST	An ArrayList object (see below)

Json Literals

The possible value of a json literal are JSON_NULL, JSON_FALSE and JSON_TRUE. When using these as a boolean value it is important to know that JSON_NULL will evaluate as true, while JSON_FALSE and JSON_True will behave as expected.

json objects

json_val* json_dict_get(json_val *dict, char *key);
int json_dict_delete(json_val *dict, char *key);
json_val *json_dict_pop(json_val *dict, char *key);
int json_dict_set(json_val *dict, char *key, json_val *val);

There are a couple of methods to access the members of the hashtable:

Json Lists

int json_list_set(json_val *arr, int index, json_val *val);
json_val *json_list_get(json_val *arr, int index);

general methods

json_val *json_val_create(int type, void *value);
void json_val_free(json_val *p);
void json_fprintf(FILE *output, json_val* jv);
void json_printf(k);
json_val *json_read_file(char *filename);
json_val *json_read_str(char *str);

(Almost all these functions and their return values are explained in the header file.)

Testing

There are a number of tests included which you can check out by running make tests && ./tests/run.py. This tries to use valgrind to check for memory leaks. If you want to disable checking for leaks add the option --no-memcheck.

Installing

Because this is kind of work in progress I have not added a way to add this to the os automatically. Instead I would recommend just linking it yourself after compiling it by running m̀ake lib. The object and header file will be in the created lib directory.