Reader


Object Hierarchy:

Object hierarchy for Reader

Description:

[ CCode ( type_id = "json_reader_get_type ()" ) ]
[ Version ( since = "0.12" ) ]
public class Reader : Object

`JsonReader` provides a simple, cursor-based API for parsing a JSON DOM.

It is similar, in spirit, to the XML Reader API.

Using `JsonReader`

```c g_autoptr(JsonParser) parser = json_parser_new ();

// str is defined elsewhere json_parser_load_from_data (parser, str, -1, NULL);

g_autoptr(JsonReader) reader = json_reader_new (json_parser_get_root (parser));

json_reader_read_member (reader, "url"); const char *url = json_reader_get_string_value (reader); json_reader_end_member (reader);

json_reader_read_member (reader, "size"); json_reader_read_element (reader, 0); int width = json_reader_get_int_value (reader); json_reader_end_element (reader); json_reader_read_element (reader, 1); int height = json_reader_get_int_value (reader); json_reader_end_element (reader); json_reader_end_member (reader); ```

Error handling

In case of error, `JsonReader` will be set in an error state; all subsequent calls will simply be ignored until a function that resets the error state is called, e.g.:

```c // ask for the 7th element; if the element does not exist, the // reader will be put in an error state json_reader_read_element (reader, 6 );

// in case of error, this will return NULL, otherwise it will // return the value of the element str = json_reader_get_string_value (value);

// this function resets the error state if any was set json_reader_end_element (reader); ```

If you want to detect the error state as soon as possible, you can use [method@Json.Reader.get_error]:

```c // like the example above, but in this case we print out the // error immediately if (!json_reader_read_element (reader, 6)) { const GError *error = json_reader_get_error (reader); g_print ("Unable to read the element: s", error->message); } ```

Example: Reader (cursor-based API):

public static int main (string[] args) {
string str = """
{
"url" : "http://www.gnome.org/img/flash/two-thirty.png",
"size" : [ 652, 242 ]
}"""
;

// Load a file:
Json.Parser parser = new Json.Parser ();
try {
parser.load_from_data (str);
} catch (Error e) {
print ("Unable to parse data: %s\n", e.message);
return -1;
}


// Create a cursor:
Json.Node node = parser.get_root ();
Json.Reader reader = new Json.Reader (node);

// Read the file:
// We use assert for format validation to keep the sample small.
string url = null;
bool has_size = false;
int64 width = -1;
int64 height = -1;

foreach (string member in reader.list_members ()) {
switch (member) {
case "url":
bool tmp = reader.read_member ("url");
assert (tmp == true);
assert (reader.is_value ());

url = reader.get_string_value ();
reader.end_member ();
break;

case "size":
bool tmp = reader.read_member ("size");
assert (tmp == true);
assert (reader.is_array ());
assert (reader.count_elements () == 2);
// Element 0:
reader.read_element (0);
assert (reader.is_value ());
width = reader.get_int_value ();
reader.end_element ();
// Element 1:
reader.read_element (1);
assert (reader.is_value ());
height = reader.get_int_value ();
reader.end_element ();
reader.end_member ();

has_size = true;
break;

default:
assert_not_reached ();
}
}

if (has_size == false || url == null) {
assert_not_reached ();
}

// Print the data:
print ("url: %s\n", url);
print ("width: %" + int64.FORMAT + "\n", width);
print ("height: %" + int64.FORMAT + "\n", height);

return 0;
}

valac --pkg json-glib-1.0 reader-example.vala


Namespace: Json
Package: json-glib-1.0

Content:

Properties:

Creation methods:

Methods:

Inherited Members: