Reader

Object Hierarchy:

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.

The cursor is moved by the `json_reader_read_*` and the `json_reader_end_*` functions. You can enter a JSON object using [ method@Json.Reader.read_member] with the name of the object member, access the value at that position, and move the cursor back one level using [method@Json.Reader.end_member]; arrays work in a similar way, using [method@Json.Reader.read_element] with the index of the element, and using [method@Json.Reader.end_element] to move the cursor back.

Using `JsonReader`

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

// str is defined elsewhere and contains: // { "url" : "http://www.gnome.org/img/flash/two-thirty.png", "size" : [ 652, 242 ] } json_parser_load_from_data (parser, str, -1, NULL);

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

// Enter the "url" member of the object json_reader_read_member (reader, "url"); const char *url = json_reader_get_string_value (reader) ; // url now contains "http://www.gnome.org/img/flash/two-thirty.png" json_reader_end_member (reader);

// Enter the "size" member of the object json_reader_read_member (reader, "size"); // Enter the first element of the array json_reader_read_element (reader, 0); int width = json_reader_get_int_value (reader); // width now contains 652 json_reader_end_element (reader); // Enter the second element of the array json_reader_read_element (reader, 1); int height = json_reader_get_int_value ( reader); // height now contains 242 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); } ```

Namespace: Json

Package: json-glib-1.0

Content:

Properties:

public Node root { owned get; set construct; }
The root of the JSON tree that the reader should read.

Creation methods:

public Reader (Node? node)
Creates a new reader.

Methods:

public int count_elements ()
Counts the elements of the current position, if the reader is positioned on an array.
public int count_members ()
Counts the members of the current position, if the reader is positioned on an object.
public void end_element ()
Moves the cursor back to the previous node after being positioned inside an array.
public void end_member ()
Moves the cursor back to the previous node after being positioned inside an object.
public bool get_boolean_value ()
Retrieves the boolean value of the current position of the reader.
public double get_double_value ()
Retrieves the floating point value of the current position of the reader.
public unowned Error? get_error ()
Retrieves the error currently set on the reader.
public int64 get_int_value ()
Retrieves the integer value of the current position of the reader.
public unowned string? get_member_name ()
Retrieves the name of the current member.
public bool get_null_value ()
Checks whether the value of the current position of the reader is `null`.
public unowned string get_string_value ()
Retrieves the string value of the current position of the reader.
public unowned Node? get_value ()
Retrieves the value node at the current position of the reader.
public bool is_array ()
Checks whether the reader is currently on an array.
public bool is_object ()
Checks whether the reader is currently on an object.
public bool is_value ()
Checks whether the reader is currently on a value.
public string[] list_members ()
Retrieves a list of member names from the current position, if the reader is positioned on an object.
public bool read_element (uint index_)
Advances the cursor of the reader to the element of the array or the member of the object at the given position.
public bool read_member (string member_name)
Advances the cursor of the reader to the `member_name` of the object at the current position.
public void set_root (Node? root)
Sets the root node of the JSON tree to be read by this.

Inherited Members:

All known members inherited from class GLib.Object