## Properties and Atoms

Properties and Atoms — Functions to manipulate properties on windows

## Synopsis

    #include <gdk/gdk.h>

    struct      GdkAtom;
    #define     GDK_ATOM_TO_POINTER             (atom)
    #define     GDK_POINTER_TO_ATOM             (ptr)
    #define     GDK_NONE
    gint        gdk_text_property_to_text_list  (GdkAtom encoding,
                                                 gint format,
                                                 const guchar *text,
                                                 gint length,
                                                 gchar ***list);
    gint        gdk_text_property_to_text_list_for_display
                                                (GdkDisplay *display,
                                                 GdkAtom encoding,
                                                 gint format,
                                                 const guchar *text,
                                                 gint length,
                                                 gchar ***list);
    void        gdk_free_text_list              (gchar **list);
    gint        gdk_text_property_to_utf8_list  (GdkAtom encoding,
                                                 gint format,
                                                 const guchar *text,
                                                 gint length,
                                                 gchar ***list);
    gint        gdk_text_property_to_utf8_list_for_display
                                                (GdkDisplay *display,
                                                 GdkAtom encoding,
                                                 gint format,
                                                 const guchar *text,
                                                 gint length,
                                                 gchar ***list);
    gint        gdk_string_to_compound_text     (const gchar *str,
                                                 GdkAtom *encoding,
                                                 gint *format,
                                                 guchar **ctext,
                                                 gint *length);
    gint        gdk_string_to_compound_text_for_display
                                                (GdkDisplay *display,
                                                 const gchar *str,
                                                 GdkAtom *encoding,
                                                 gint *format,
                                                 guchar **ctext,
                                                 gint *length);
    void        gdk_free_compound_text          (guchar *ctext);
    gchar*      gdk_utf8_to_string_target       (const gchar *str);
    gboolean    gdk_utf8_to_compound_text       (const gchar *str,
                                                 GdkAtom *encoding,
                                                 gint *format,
                                                 guchar **ctext,
                                                 gint *length);
    gboolean    gdk_utf8_to_compound_text_for_display
                                                (GdkDisplay *display,
                                                 const gchar *str,
                                                 GdkAtom *encoding,
                                                 gint *format,
                                                 guchar **ctext,
                                                 gint *length);
    GdkAtom     gdk_atom_intern                 (const gchar *atom_name,
                                                 gboolean only_if_exists);
    gchar*      gdk_atom_name                   (GdkAtom atom);
    gboolean    gdk_property_get                (GdkWindow *window,
                                                 GdkAtom property,
                                                 GdkAtom type,
                                                 gulong offset,
                                                 gulong length,
                                                 gint pdelete,
                                                 GdkAtom *actual_property_type,
                                                 gint *actual_format,
                                                 gint *actual_length,
                                                 guchar **data);
    void        gdk_property_change             (GdkWindow *window,
                                                 GdkAtom property,
                                                 GdkAtom type,
                                                 gint format,
                                                 GdkPropMode mode,
                                                 const guchar *data,
                                                 gint nelements);
    enum        GdkPropMode;
    void        gdk_property_delete             (GdkWindow *window,
                                                 GdkAtom property);

## Description

Each window under X can have any number of associated properties attached to it. Properties are arbitrary chunks of data identified by atoms. (An atom is a numeric index into a string table on the X server. They are used to transfer strings efficiently between clients without having to transfer the entire string.) A property has an associated type, which is also identified using an atom.

A property has an associated format, an integer describing how many bits are in each unit of data inside the property. It must be 8, 16, or 32. When data is transferred between the server and client, if they are of different endianesses it will be byteswapped as necessary according to the format of the property. Note that on the client side, properties of format 32 will be stored with one unit per long, even if a long integer has more than 32 bits on the platform. (This decision was apparently made for Xlib to maintain compatibility with programs that assumed longs were 32 bits, at the expense of programs that knew better.)

The functions in this section are used to add, remove and change properties on windows, to convert atoms to and from strings and to manipulate some types of data commonly stored in X window properties.

## Details

### struct GdkAtom

    struct GdkAtom;

An opaque type representing a string as an index into a table of strings on the X server.

### GDK_ATOM_TO_POINTER()

    #define GDK_ATOM_TO_POINTER(atom) (atom)

Converts a GdkAtom into a pointer type.

`atom` : | a GdkAtom.

### GDK_POINTER_TO_ATOM()

    #define GDK_POINTER_TO_ATOM(ptr)  ((GdkAtom)(ptr))

Extracts a GdkAtom from a pointer. The GdkAtom must have been stored in the pointer with GDK_ATOM_TO_POINTER().

`ptr` : | a pointer containing a GdkAtom.

### GDK_NONE

    #define GDK_NONE            _GDK_MAKE_ATOM (0)

A null value for GdkAtom, used in a similar way as `None` in the Xlib API.

### gdk_text_property_to_text_list ()

    gint        gdk_text_property_to_text_list  (GdkAtom encoding,
                                                 gint format,
                                                 const guchar *text,
                                                 gint length,
                                                 gchar ***list);

Converts a text string from the encoding as it is stored in a property into an array of strings in the encoding of the current local. (The elements of the array represent the nul-separated elements of the original text string.)

`encoding` : | an atom representing the encoding. The most common values for this are `STRING`, or `COMPOUND_TEXT`. This is value used as the type for the property.
`format` : | the format of the property.
`text` : | the text data.
`length` : | the length of the property, in items.
`list` : | location to store a terminated array of strings in the encoding of the current locale. This array should be freed using gdk_free_text_list().
Returns : | the number of strings stored in `list`, or 0, if the conversion failed.

### gdk_text_property_to_text_list_for_display ()

    gint        gdk_text_property_to_text_list_for_display
                                                (GdkDisplay *display,
                                                 GdkAtom encoding,
                                                 gint format,
                                                 const guchar *text,
                                                 gint length,
                                                 gchar ***list);

Convert a text string from the encoding as it is stored in a property into an array of strings in the encoding of the current locale. (The elements of the array represent the nul-separated elements of the original text string.)

`display` : | The GdkDisplay where the encoding is defined.
`encoding` : | an atom representing the encoding. The most common values for this are STRING, or COMPOUND_TEXT. This is value used as the type for the property.
`format` : | the format of the property.
`text` : | The text data.
`length` : | The number of items to transform.
`list` : | location to store a terminated array of strings in the encoding of the current locale. This array should be freed using gdk_free_text_list().
Returns : | the number of strings stored in list, or 0, if the conversion failed.

Since 2.2

### gdk_free_text_list ()

    void        gdk_free_text_list              (gchar **list);

Frees the array of strings created by gdk_text_property_to_text_list().

`list` : | the value stored in the `list` parameter by a call to gdk_text_property_to_text_list().

### gdk_text_property_to_utf8_list ()

    gint        gdk_text_property_to_utf8_list  (GdkAtom encoding,
                                                 gint format,
                                                 const guchar *text,
                                                 gint length,
                                                 gchar ***list);

Convert a text property in the giving encoding to a list of UTF-8 strings.

`encoding` : | an atom representing the encoding of the text
`format` : | the format of the property
`text` : | the text to convert
`length` : | the length of `text`, in bytes
`list` : | location to store the list of strings or `NULL`. The list should be freed with g_strfreev().
Returns : | the number of strings in the resulting list.

### gdk_text_property_to_utf8_list_for_display ()

    gint        gdk_text_property_to_utf8_list_for_display
                                                (GdkDisplay *display,
                                                 GdkAtom encoding,
                                                 gint format,
                                                 const guchar *text,
                                                 gint length,
                                                 gchar ***list);

Converts a text property in the given encoding to a list of UTF-8 strings.

`display` : | a GdkDisplay
`encoding` : | an atom representing the encoding of the text
`format` : | the format of the property
`text` : | the text to convert
`length` : | the length of `text`, in bytes
`list` : | location to store the list of strings or `NULL`. The list should be freed with g_strfreev().
Returns : | the number of strings in the resulting list.

Since 2.2

### gdk_string_to_compound_text ()

    gint        gdk_string_to_compound_text     (const gchar *str,
                                                 GdkAtom *encoding,
                                                 gint *format,
                                                 guchar **ctext,
                                                 gint *length);

Converts a string from the encoding of the current locale into a form suitable for storing in a window property.

`str` : | a nul-terminated string.
`encoding` : | location to store the encoding atom (to be used as the type for the property).
`format` : | location to store the format for the property.
`ctext` : | location to store newly allocated data for the property.
`length` : | location to store the length of `ctext` in items.
Returns : | 0 upon sucess, non-zero upon failure.

### gdk_string_to_compound_text_for_display ()

    gint        gdk_string_to_compound_text_for_display
                                                (GdkDisplay *display,
                                                 const gchar *str,
                                                 GdkAtom *encoding,
                                                 gint *format,
                                                 guchar **ctext,
                                                 gint *length);

Convert a string from the encoding of the current locale into a form suitable for storing in a window property.

`display` : | the GdkDisplay where the encoding is defined.
`str` : | a nul-terminated string.
`encoding` : | location to store the encoding atom (to be used as the type for the property).
`format` : | location to store the format of the property
`ctext` : | location to store newly allocated data for the property.
`length` : | the length of `text`, in bytes
Returns : | 0 upon sucess, non-zero upon failure.

Since 2.2

### gdk_free_compound_text ()

    void        gdk_free_compound_text          (guchar *ctext);

Frees the data returned from gdk_string_to_compound_text().

`ctext` : | The pointer stored in `ctext` from a call to gdk_string_to_compound_text().

### gdk_utf8_to_string_target ()

    gchar*      gdk_utf8_to_string_target       (const gchar *str);

Converts an UTF-8 string into the best possible representation as a STRING. The representation of characters not in STRING is not specified; it may be as pseudo-escape sequences \x{ABCD}, or it may be in some other form of approximation.

`str` : | a UTF-8 string
Returns : | the newly-allocated string, or `NULL` if the conversion failed. (It should not fail for any properly formed UTF-8 string unless system limits like memory or file descriptors are exceeded.)

### gdk_utf8_to_compound_text ()

    gboolean    gdk_utf8_to_compound_text       (const gchar *str,
                                                 GdkAtom *encoding,
                                                 gint *format,
                                                 guchar **ctext,
                                                 gint *length);

Convert from UTF-8 to compound text.

`str` : | a UTF-8 string
`encoding` : | location to store resulting encoding
`format` : | location to store format of the result
`ctext` : | location to store the data of the result
`length` : | location to store the length of the data stored in `ctext`
Returns : | `TRUE` if the conversion succeeded, otherwise false.

### gdk_utf8_to_compound_text_for_display ()

    gboolean    gdk_utf8_to_compound_text_for_display
                                                (GdkDisplay *display,
                                                 const gchar *str,
                                                 GdkAtom *encoding,
                                                 gint *format,
                                                 guchar **ctext,
                                                 gint *length);

Converts from UTF-8 to compound text.

`display` : | a GdkDisplay
`str` : | a UTF-8 string
`encoding` : | location to store resulting encoding
`format` : | location to store format of the result
`ctext` : | location to store the data of the result
`length` : | location to store the length of the data stored in `ctext`
Returns : | `TRUE` if the conversion succeeded, otherwise `FALSE`.

Since 2.2

### gdk_atom_intern ()

    GdkAtom     gdk_atom_intern                 (const gchar *atom_name,
                                                 gboolean only_if_exists);

Finds or creates an atom corresponding to a given string.

`atom_name` : | a string.
`only_if_exists` : | if `TRUE`, do not create a new atom, but just return the atom if it already exists.
Returns : | the atom corresponding to `atom_name`, or, if `only_if_exists` is `TRUE`, and an atom does not already exists for the string, `GDK_NONE`.

### gdk_atom_name ()

    gchar*      gdk_atom_name                   (GdkAtom atom);

Determines the string corresponding to an atom.

`atom` : | a GdkAtom.
Returns : | a newly-allocated string containing the string corresponding to `atom`. When you are done with the return value, you should free it using g_free().

### gdk_property_get ()

    gboolean    gdk_property_get                (GdkWindow *window,
                                                 GdkAtom property,
                                                 GdkAtom type,
                                                 gulong offset,
                                                 gulong length,
                                                 gint pdelete,
                                                 GdkAtom *actual_property_type,
                                                 gint *actual_format,
                                                 gint *actual_length,
                                                 guchar **data);

Retrieves a portion of the contents of a property. If the property does not exist, then the function returns `FALSE`, and `GDK_NONE` will be stored in `actual_property_type`.

### Note

The `XGetWindowProperty()` function that gdk_property_get() uses has a very confusing and complicated set of semantics. Unfortunately, gdk_property_get() makes the situation worse instead of better (the semantics should be considered undefined), and also prints warnings to stderr in cases where it should return a useful error to the program. You are advised to use `XGetWindowProperty()` directly until a replacement function for gdk_property_get() is provided.

`window` : | a GdkWindow.
`property` : | the property to retrieve.
`type` : | the desired property type, or 0, if any type of data is acceptable. If this does not match the actual type, then `actual_format` and `actual_length` will be filled in, a warning will be printed to stderr and no data will be returned.
`offset` : | the offset into the property at which to begin retrieving data. (in 4 byte units!)
`length` : | the length of the data to delete. (in bytes, but the actual retrieved length will be the next integer multiple multiple of four greater than this!)
`pdelete` : | if `TRUE`, delete the property after retrieving the data.
`actual_property_type` : | location to store the actual type of the property.
`actual_format` : | location to store the actual format of the data.
`actual_length` : | location to store the length of the retrieved data, in bytes.
`data` : | location to store a pointer to the data. The retrieved data should be freed with g_free() when you are finished using it.
Returns : | `TRUE` if data was sucessfully received and stored in `data`, otherwise `FALSE`.

### gdk_property_change ()

    void        gdk_property_change             (GdkWindow *window,
                                                 GdkAtom property,
                                                 GdkAtom type,
                                                 gint format,
                                                 GdkPropMode mode,
                                                 const guchar *data,
                                                 gint nelements);

Changes the contents of a property on a window.

`window` : | a GdkWindow.
`property` : | the property to change.
`type` : | the new type for the property. If `mode` is `GDK_PROP_MODE_PREPEND` or `GDK_PROP_MODE_APPEND`, then this must match the existing type or an error will occur.
`format` : | the new format for the property. If `mode` is `GDK_PROP_MODE_PREPEND` or `GDK_PROP_MODE_APPEND`, then this must match the existing format or an error will occur.
`mode` : | a value describing how the new data is to be combined with the current data.
`data` : | the data (a `guchar *` `gushort *`, or `gulong *`, depending on `format`), cast to a `guchar *`.
`nelements` : | the number of elements of size determined by the format, contained in `data`.

### enum GdkPropMode

    typedef enum
    {
      GDK_PROP_MODE_REPLACE,
      GDK_PROP_MODE_PREPEND,
      GDK_PROP_MODE_APPEND
    } GdkPropMode;

Describes how existing data is combined with new data when using gdk_property_change().

`GDK_PROP_MODE_REPLACE` | the new data replaces the existing data.
`GDK_PROP_MODE_PREPEND` | the new data is prepended to the existing data.
`GDK_PROP_MODE_APPEND` | the new data is appended to the existing data.

### gdk_property_delete ()

    void        gdk_property_delete             (GdkWindow *window,
                                                 GdkAtom property);

Deletes a property from a window.

`window` : | a GdkWindow.
`property` : | the property to delete.