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);
}

 

SEE ALSO

xcb-requests(3), xcb-examples(3), xcb_intern_atom(3), xprop(1)  

AUTHOR

Generated from xproto.xml. Contact xcb@lists.freedesktop.org for corrections and improvements.

---

 

Index

NAME

SYNOPSIS

Request function

Reply datastructure

Reply function

Reply accessors

REQUEST ARGUMENTS

REPLY FIELDS

DESCRIPTION

RETURN VALUE

ERRORS

EXAMPLE

SEE ALSO

AUTHOR