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Known Implementations
GSeekable is implemented by GBufferedInputStream, GBufferedOutputStream, GDataInputStream, GDataOutputStream, GFileIOStream, GFileInputStream, GFileOutputStream, GMemoryInputStream and GMemoryOutputStream.
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.
g_seekable_can_seek ()
gboolean
g_seekable_can_seek (GSeekable *seekable);
Tests if the stream supports the GSeekableIface.
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.
g_seekable_can_truncate ()
gboolean
g_seekable_can_truncate (GSeekable *seekable);
Tests if the length of the stream can be adjusted with
g_seekable_truncate().
g_seekable_truncate ()
gboolean g_seekable_truncate (GSeekable *seekable,goffset offset,GCancellable *cancellable,GError **error);
Sets the length of the stream to offset
. If the stream was previously
larger than offset
, the extra data is discarded. If the stream was
previouly shorter than offset
, it is extended with NUL ('\0') bytes.
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 |
new length for |
|
cancellable |
optional GCancellable object, |
[nullable] |
error |
a GError location to store the error occurring, or |
Types and Values
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.