## GSeekable

GSeekable — Stream seeking interface

## Synopsis

    #include <gio/gio.h>

                        GSeekable;
    struct              GSeekableIface;
    goffset             g_seekable_tell                     (GSeekable *seekable);
    gboolean            g_seekable_can_seek                 (GSeekable *seekable);
    gboolean            g_seekable_seek                     (GSeekable *seekable,
                                                             goffset offset,
                                                             GSeekType type,
                                                             GCancellable *cancellable,
                                                             GError **error);
    gboolean            g_seekable_can_truncate             (GSeekable *seekable);
    gboolean            g_seekable_truncate                 (GSeekable *seekable,
                                                             goffset offset,
                                                             GCancellable *cancellable,
                                                             GError **error);

## Object Hierarchy

      GInterface
       +----GSeekable

## Prerequisites

GSeekable requires GObject.

## Known Implementations

GSeekable is implemented by GFileIOStream, GFileInputStream, GFileOutputStream, GMemoryInputStream and GMemoryOutputStream.

## Description

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

## Details

### 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.

GTypeInterface `g_iface`; | The parent interface.
`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` () | Chekcs if truncation is suppored by the stream.
`truncate_fn` () | Truncates a stream.

### g_seekable_tell ()

    goffset             g_seekable_tell                     (GSeekable *seekable);

Tells the current position within the stream.

`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.

`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`.

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.

`seekable` : | a GSeekable.
`offset` : | a goffset.
`type` : | a GSeekType.
`cancellable` : | optional GCancellable object, `NULL` to ignore. [allow-none]
`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.

`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

`seekable` : | a GSeekable.
`offset` : | a goffset.
`cancellable` : | optional GCancellable object, `NULL` to ignore. [allow-none]
`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.

## See Also

GInputStream, GOutputStream