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GSeekable

GSeekable — Stream seeking interface

Types and Values

Object Hierarchy

    GInterface
    ╰── GSeekable

Prerequisites

GSeekable requires GObject.

Includes

#include <gio/gio.h>

Description

GSeekable is implemented by streams (implementations of GInputStream or GOutputStream) that support seeking.

Seekable streams largely fall into two categories: resizable and fixed-size.

GSeekable on fixed-sized streams is approximately the same as POSIX lseek() on a block device (for example: attmepting to seek past the end of the device is an error). Fixed streams typically cannot be truncated.

GSeekable on resizable streams is approximately the same as POSIX lseek() on a normal file. Seeking past the end and writing data will usually cause the stream to resize by introducing zero bytes.

Functions

g_seekable_tell ()

goffset
g_seekable_tell (GSeekable *seekable);

Tells the current position within the stream.

Parameters

seekable

a GSeekable.

 

Returns

the offset from the beginning of the buffer.


g_seekable_can_seek ()

gboolean
g_seekable_can_seek (GSeekable *seekable);

Tests if the stream supports the GSeekableIface.

Parameters

seekable

a GSeekable.

 

Returns

TRUE if seekable can be seeked. FALSE otherwise.


g_seekable_seek ()

gboolean
g_seekable_seek (GSeekable *seekable,
                 goffset offset,
                 GSeekType type,
                 GCancellable *cancellable,
                 GError **error);

Seeks in the stream by the given offset , modified by type .

Attempting to seek past the end of the stream will have different results depending on if the stream is fixed-sized or resizable. If the stream is resizable then seeking past the end and then writing will result in zeros filling the empty space. Seeking past the end of a resizable stream and reading will result in EOF. Seeking past the end of a fixed-sized stream will fail.

Any operation that would result in a negative offset will fail.

If cancellable is not NULL, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error G_IO_ERROR_CANCELLED will be returned.

Parameters

seekable

a GSeekable.

 

offset

a goffset.

 

type

a GSeekType.

 

cancellable

optional GCancellable object, NULL to ignore.

[nullable]

error

a GError location to store the error occurring, or NULL to ignore.

 

Returns

TRUE if successful. If an error has occurred, this function will return FALSE and set error appropriately if present.


g_seekable_can_truncate ()

gboolean
g_seekable_can_truncate (GSeekable *seekable);

Tests if the stream can be truncated.

Parameters

seekable

a GSeekable.

 

Returns

TRUE if the stream can be truncated, FALSE otherwise.


g_seekable_truncate ()

gboolean
g_seekable_truncate (GSeekable *seekable,
                     goffset offset,
                     GCancellable *cancellable,
                     GError **error);

Truncates a stream with a given offset.

If cancellable is not NULL, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error G_IO_ERROR_CANCELLED will be returned. If an operation was partially finished when the operation was cancelled the partial result will be returned, without an error.

Virtual: truncate_fn

Parameters

seekable

a GSeekable.

 

offset

a goffset.

 

cancellable

optional GCancellable object, NULL to ignore.

[nullable]

error

a GError location to store the error occurring, or NULL to ignore.

 

Returns

TRUE if successful. If an error has occurred, this function will return FALSE and set error appropriately if present.

Types and Values

GSeekable

typedef struct _GSeekable GSeekable;

Seek object for streaming operations.


struct GSeekableIface

struct GSeekableIface {
  GTypeInterface g_iface;

  /* Virtual Table */

  goffset     (* tell)	         (GSeekable    *seekable);

  gboolean    (* can_seek)       (GSeekable    *seekable);
  gboolean    (* seek)	         (GSeekable    *seekable,
				  goffset       offset,
				  GSeekType     type,
				  GCancellable *cancellable,
				  GError      **error);

  gboolean    (* can_truncate)   (GSeekable    *seekable);
  gboolean    (* truncate_fn)    (GSeekable    *seekable,
				  goffset       offset,
				  GCancellable *cancellable,
				  GError       **error);

  /* TODO: Async seek/truncate */
};

Provides an interface for implementing seekable functionality on I/O Streams.

Members

tell ()

Tells the current location within a stream.

 

can_seek ()

Checks if seeking is supported by the stream.

 

seek ()

Seeks to a location within a stream.

 

can_truncate ()

Checks if truncation is supported by the stream.

 

truncate_fn ()

Truncates a stream.

 
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