A simple and complete json parser
Posted by Joys of Programming on in json-c
This parser makes use of all the functions which reads the value of a json object. This parser is complete in all respects. You can make use of the functions to create parser for your various requirements
#include <json/json.h>
#include <stdio.h>
/*printing the value corresponding to boolean, double, integer and strings*/
void print_json_value(json_object *jobj){
enum json_type type;
printf("type: ",type);
type = json_object_get_type(jobj); /*Getting the type of the json object*/
switch (type) {
case json_type_boolean: printf("json_type_boolean\n");
printf("value: %s\n", json_object_get_boolean(jobj)? "true": "false");
break;
case json_type_double: printf("json_type_double\n");
printf(" value: %lf\n", json_object_get_double(jobj));
break;
case json_type_int: printf("json_type_int\n");
printf(" value: %d\n", json_object_get_int(jobj));
break;
case json_type_string: printf("json_type_string\n");
printf(" value: %s\n", json_object_get_string(jobj));
break;
}
}
void json_parse_array( json_object *jobj, char *key) {
void json_parse(json_object * jobj); /*Forward Declaration*/
enum json_type type;
json_object *jarray = jobj; /*Simply get the array*/
if(key) {
jarray = json_object_object_get(jobj, key); /*Getting the array if it is a key value pair*/
}
int arraylen = json_object_array_length(jarray); /*Getting the length of the array*/
printf("Array Length: %d\n",arraylen);
int i;
json_object * jvalue;
for (i=0; i< arraylen; i++){
jvalue = json_object_array_get_idx(jarray, i); /*Getting the array element at position i*/
type = json_object_get_type(jvalue);
if (type == json_type_array) {
json_parse_array(jvalue, NULL);
}
else if (type != json_type_object) {
printf("value[%d]: ",i);
print_json_value(jvalue);
}
else {
json_parse(jvalue);
}
}
}
/*Parsing the json object*/
void json_parse(json_object * jobj) {
enum json_type type;
json_object_object_foreach(jobj, key, val) { /*Passing through every array element*/
printf("type: ",type);
type = json_object_get_type(val);
switch (type) {
case json_type_boolean:
case json_type_double:
case json_type_int:
case json_type_string: print_json_value(val);
break;
case json_type_object: printf("json_type_object\n");
jobj = json_object_object_get(jobj, key);
json_parse(jobj);
break;
case json_type_array: printf("type: json_type_array, ");
json_parse_array(jobj, key);
break;
}
}
}
int main() {
char * string = "{\"sitename\" : \"joys of programming\",\
\"categories\" : [ \"c\" , [\"c++\" , \"c\" ], \"java\", \"PHP\" ],\
\"author-details\": { \"admin\": false, \"name\" : \"Joys of Programming\", \"Number of Posts\" : 10 } \
}";
printf("JSON string: %s\n", string);
json_object * jobj = json_tokener_parse(string);
json_parse(jobj);
}
The output of the program is something like this
JSON string: {"sitename" : "joys of programming", "categories" : [ "c" , ["c++" , "c" ], "java", "PHP" ], "author-details": { "admin": false, "name" : "Joys of Programming", "Number of Posts" : 10 } }
type: type: json_type_string
value: joys of programming
type: type: json_type_array, Array Length: 4
value[0]: type: json_type_string
value: c
Array Length: 2
value[0]: type: json_type_string
value: c++
value[1]: type: json_type_string
value: c
value[2]: type: json_type_string
value: java
value[3]: type: json_type_string
value: PHP
type: json_type_object
type: type: json_type_boolean
value: false
type: type: json_type_string
value: Joys of Programming
type: type: json_type_int
value: 10
Comments:
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I’ve got Segmentation fault when I try any of JSON functions with data from: http://search.twitter.com/search.json?q=from:niebezpiecznik&rpp=1&page=1
Is it possible to test if object is JSON object?
Can you point me a snippet of your code? In the meantime, check the function json_object_get_type(). It will help you find that.
I’ve experienced segmentation faults as well. Problem was that the sample code above cannot handle JSON objects that contains a NULL value (json_type_null).
The segfault happens if you have a JSON object that contains another JSON object as one of its values. Specifically, you’ll only see it happen if the sub-object is not the last item parsed. This is because inside the json_parse method, jobj gets reassigned and on subsequent passes through the foreach the expected keys won’t be found. You can fix it pretty easily by just taking out the assignment and passing json_object_object_get directly to the recursive call on json_parse.
Before:
case json_type_object: printf("json_type_object\n");
jobj = json_object_object_get(jobj, key);
json_parse(jobj);
break;
After:
case json_type_object: printf("json_type_object\n");
json_parse(json_object_object_get(jobj, key));
break;
Code from Mike caused a loop for me, i use the following code:
case json_type_object:
printf("json_type_object\n");
json_object *jobj2 = json_object_object_get(jobj, key);
json_parse(jobj2);
break;