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You are here: manpages

xcb_get_property

Section: XCB Requests (3)
Updated: libxcb 1.12
Index Return to Main Contents

NAME

xcb_get_property - Gets a window property

SYNOPSIS

#include <xcb/xproto.h>

Request function

: xcb_get_property_cookie_t xcb_get_property(xcb_connection_t *conn, uint8_t _delete, xcb_window_t window, xcb_atom_t property, xcb_atom_t type, uint32_t long_offset, uint32_t long_length);

Reply datastructure


typedef struct xcb_get_property_reply_t {
    uint8_t    response_type;
    uint8_t    format;
    uint16_t   sequence;
    uint32_t   length;
    xcb_atom_t type;
    uint32_t   bytes_after;
    uint32_t   value_len;
    uint8_t    pad0[12];
} xcb_get_property_reply_t;

Reply function

: xcb_get_property_reply_t *xcb_get_property_reply(xcb_connection_t *conn, xcb_get_property_cookie_t cookie, xcb_generic_error_t **e);

Reply accessors

: void *xcb_get_property_value(const xcb_get_property_request_t *reply);
: int xcb_get_property_value_length(const xcb_get_property_reply_t *reply);
: xcb_generic_iterator_t xcb_get_property_value_end(const xcb_get_property_reply_t *reply);

REQUEST ARGUMENTS

conn: The XCB connection to X11.
_delete: Whether the property should actually be deleted. For deleting a property, the specified type has to match the actual property type.
window: The window whose property you want to get.
property: The property you want to get (an atom).
type: The type of the property you want to get (an atom).
long_offset: Specifies the offset (in 32-bit multiples) in the specified property where the data is to be retrieved.
long_length: Specifies how many 32-bit multiples of data should be retrieved (e.g. if you set long_length to 4, you will receive 16 bytes of data).

REPLY FIELDS

response_type: The type of this reply, in this case XCB_GET_PROPERTY. This field is also present in the xcb_generic_reply_t and can be used to tell replies apart from each other.
sequence: The sequence number of the last request processed by the X11 server.
length: The length of the reply, in words (a word is 4 bytes).
format: Specifies whether the data should be viewed as a list of 8-bit, 16-bit, or 32-bit quantities. Possible values are 8, 16, and 32. This information allows the X server to correctly perform byte-swap operations as necessary.
type: The actual type of the property (an atom).
bytes_after: The number of bytes remaining to be read in the property if a partial read was performed.
value_len: The length of value. You should use the corresponding accessor instead of this field.

DESCRIPTION

Gets the specified property from the specified window. Properties are for example the window title (WM_NAME) or its minimum size (WM_NORMAL_HINTS). Protocols such as EWMH also use properties - for example EWMH defines the window title, encoded as UTF-8 string, in the _NET_WM_NAME property.

TODO: talk about type

TODO: talk about delete

TODO: talk about the offset/length thing. what's a valid use case?

RETURN VALUE

Returns an xcb_get_property_cookie_t. Errors have to be handled when calling the reply function xcb_get_property_reply.

If you want to handle errors in the event loop instead, use xcb_get_property_unchecked. See xcb-requests(3) for details.

ERRORS

xcb_atom_error_t: property or type do not refer to a valid atom.
xcb_value_error_t: The specified long_offset is beyond the actual property length (e.g. the property has a length of 3 bytes and you are setting long_offset to 1, resulting in a byte offset of 4).
xcb_window_error_t: The specified window does not exist.

EXAMPLE


/*
 * Prints the WM_NAME property of the window.
 *
 */
void my_example(xcb_connection_t *c, xcb_window_t window) {
    xcb_get_property_cookie_t cookie;
    xcb_get_property_reply_t *reply;

    /* These atoms are predefined in the X11 protocol. */
    xcb_atom_t property = XCB_ATOM_WM_NAME;
    xcb_atom_t type = XCB_ATOM_STRING;

    // TODO: a reasonable long_length for WM_NAME?
    cookie = xcb_get_property(c, 0, window, property, type, 0, 0);
    if ((reply = xcb_get_property_reply(c, cookie, NULL))) {
        int len = xcb_get_property_value_length(reply);
        if (len == 0) {
            printf("TODO\n");
            free(reply);
            return;
        }
        printf("WM_NAME is %.*s\n", len,
               (char*)xcb_get_property_value(reply));
    }
    free(reply);
}