GLib Reference Manual
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# IO Channels

## Name

IO Channels -- portable support for using files, pipes and sockets.

## Synopsis

    #include <glib.h>

    struct      GIOChannel;

    GIOChannel* g_io_channel_unix_new           (int fd);
    gint        g_io_channel_unix_get_fd        (GIOChannel *channel);

    void        g_io_channel_init               (GIOChannel *channel);

    GIOChannel* g_io_channel_new_file           (const gchar *filename,
                                                 const gchar *mode,
                                                 GError **error);
    GIOStatus   g_io_channel_read_chars         (GIOChannel *channel,
                                                 gchar *buf,
                                                 gsize count,
                                                 gsize *bytes_read,
                                                 GError **error);
    GIOStatus   g_io_channel_read_unichar       (GIOChannel *channel,
                                                 gunichar *thechar,
                                                 GError **error);
    GIOStatus   g_io_channel_read_line          (GIOChannel *channel,
                                                 gchar **str_return,
                                                 gsize *length,
                                                 gsize *terminator_pos,
                                                 GError **error);
    GIOStatus   g_io_channel_read_line_string   (GIOChannel *channel,
                                                 GString *buffer,
                                                 gsize *terminator_pos,
                                                 GError **error);
    GIOStatus   g_io_channel_read_to_end        (GIOChannel *channel,
                                                 gchar **str_return,
                                                 gsize *length,
                                                 GError **error);
    GIOStatus   g_io_channel_write_chars        (GIOChannel *channel,
                                                 const gchar *buf,
                                                 gssize count,
                                                 gsize *bytes_written,
                                                 GError **error);
    GIOStatus   g_io_channel_write_unichar      (GIOChannel *channel,
                                                 gunichar thechar,
                                                 GError **error);
    GIOStatus   g_io_channel_flush              (GIOChannel *channel,
                                                 GError **error);
    GIOStatus   g_io_channel_seek_position      (GIOChannel *channel,
                                                 gint64 offset,
                                                 GSeekType type,
                                                 GError **error);
    enum        GSeekType;
    GIOStatus   g_io_channel_shutdown           (GIOChannel *channel,
                                                 gboolean flush,
                                                 GError **err);

    enum        GIOStatus;
    enum        GIOChannelError;
    #define     G_IO_CHANNEL_ERROR
    GIOChannelError g_io_channel_error_from_errno
                                                (gint en);

    void        g_io_channel_ref                (GIOChannel *channel);
    void        g_io_channel_unref              (GIOChannel *channel);

    GSource*    g_io_create_watch               (GIOChannel *channel,
                                                 GIOCondition condition);
    guint       g_io_add_watch                  (GIOChannel *channel,
                                                 GIOCondition condition,
                                                 GIOFunc func,
                                                 gpointer user_data);
    guint       g_io_add_watch_full             (GIOChannel *channel,
                                                 gint priority,
                                                 GIOCondition condition,
                                                 GIOFunc func,
                                                 gpointer user_data,
                                                 GDestroyNotify notify);
    enum        GIOCondition;
    gboolean    (*GIOFunc)                      (GIOChannel *source,
                                                 GIOCondition condition,
                                                 gpointer data);

    struct      GIOFuncs;

    gsize       g_io_channel_get_buffer_size    (GIOChannel *channel);
    void        g_io_channel_set_buffer_size    (GIOChannel *channel,
                                                 gsize size);
    GIOCondition g_io_channel_get_buffer_condition
                                                (GIOChannel *channel);
    GIOFlags    g_io_channel_get_flags          (GIOChannel *channel);
    GIOStatus   g_io_channel_set_flags          (GIOChannel *channel,
                                                 GIOFlags flags,
                                                 GError **error);
    enum        GIOFlags;
    G_CONST_RETURN gchar* g_io_channel_get_line_term
                                                (GIOChannel *channel,
                                                 gint *length);
    void        g_io_channel_set_line_term      (GIOChannel *channel,
                                                 const gchar *line_term,
                                                 gint length);
    gboolean    g_io_channel_get_buffered       (GIOChannel *channel);
    void        g_io_channel_set_buffered       (GIOChannel *channel,
                                                 gboolean buffered);
    G_CONST_RETURN gchar* g_io_channel_get_encoding
                                                (GIOChannel *channel);
    GIOStatus   g_io_channel_set_encoding       (GIOChannel *channel,
                                                 const gchar *encoding,
                                                 GError **error);
    gboolean    g_io_channel_get_close_on_unref (GIOChannel *channel);
    void        g_io_channel_set_close_on_unref (GIOChannel *channel,
                                                 gboolean do_close);

    GIOError    g_io_channel_read               (GIOChannel *channel,
                                                 gchar *buf,
                                                 gsize count,
                                                 gsize *bytes_read);
    enum        GIOError;
    GIOError    g_io_channel_write              (GIOChannel *channel,
                                                 const gchar *buf,
                                                 gsize count,
                                                 gsize *bytes_written);
    GIOError    g_io_channel_seek               (GIOChannel *channel,
                                                 gint64 offset,
                                                 GSeekType type);
    void        g_io_channel_close              (GIOChannel *channel);

## Description

The GIOChannel data type aims to provide a portable method for using file descriptors, pipes, and sockets, and integrating them into the main event loop. Currently full support is available on UNIX platforms, support for Windows is only partially complete.

To create a new GIOChannel on UNIX systems use g_io_channel_unix_new(). This works for plain file descriptors, pipes and sockets. Alternatively, a channel can be created for a file in a system independent manner using g_io_channel_new_file().

Once a GIOChannel has been created, it can be used in a generic manner with the functions g_io_channel_read_chars(), g_io_channel_write_chars(), g_io_channel_seek_position(), and g_io_channel_close().

To add a GIOChannel to the main event loop use g_io_add_watch() or g_io_add_watch_full(). Here you specify which events you are interested in on the GIOChannel, and provide a function to be called whenever these events occur.

GIOChannel instances are created with an initial reference count of 1. g_io_channel_ref() and g_io_channel_unref() can be used to increment or decrement the reference count respectively. When the reference count falls to 0, the GIOChannel is freed. (Though it isn't closed automatically, unless it was created using g_io_channel_new_from_file().) Using g_io_add_watch() or g_io_add_watch_full() increments a channel's reference count.

GTK+ contains the convenience function gtk_input_add_full() which creates a GIOChannel from a file descriptor and adds it to the main event loop. The event source can later be removed with gtk_input_remove(). Similar functions can also be found in GDK.

The new functions g_io_channel_read_chars(), g_io_channel_read_line(), g_io_channel_read_line_string(), g_io_channel_read_to_end(), g_io_channel_write_chars(), g_io_channel_seek_position(), and g_io_channel_flush() should not be mixed with the deprecated functions g_io_channel_read(), g_io_channel_write(), and g_io_channel_seek() on the same channel.

## Details

### struct GIOChannel

    struct GIOChannel
    {
      /*< private >*/
      guint ref_count;
      GIOFuncs *funcs;

      gchar *encoding;
      GIConv read_cd;
      GIConv write_cd;
      gchar *line_term;		/* String which indicates the end of a line of text */
      guint line_term_len;		/* So we can have null in the line term */

      gsize buf_size;
      GString *read_buf;		/* Raw data from the channel */
      GString *encoded_read_buf;    /* Channel data converted to UTF-8 */
      GString *write_buf;		/* Data ready to be written to the file */
      gchar partial_write_buf[6];	/* UTF-8 partial characters, null terminated */

      /* Group the flags together, immediately after partial_write_buf, to save memory */

      guint use_buffer     : 1;	/* The encoding uses the buffers */
      guint do_encode      : 1;	/* The encoding uses the GIConv coverters */
      guint close_on_unref : 1;	/* Close the channel on final unref */
      guint is_readable    : 1;	/* Cached GIOFlag */
      guint is_writeable   : 1;	/* ditto */
      guint is_seekable    : 1;	/* ditto */

      gpointer reserved1;
      gpointer reserved2;
    };

A data structure representing an IO Channel. The fields should be considered private and should only be accessed with the following functions.

### g_io_channel_unix_new ()

    GIOChannel* g_io_channel_unix_new           (int fd);

Creates a new GIOChannel given a file descriptor. On UNIX systems this works for plain files, pipes, and sockets.

The returned GIOChannel has a reference count of 1.

`fd` : | a file descriptor.
Returns : | a new GIOChannel.

### g_io_channel_unix_get_fd ()

    gint        g_io_channel_unix_get_fd        (GIOChannel *channel);

Returns the file descriptor of the UNIX GIOChannel.

`channel` : | a GIOChannel, created with g_io_channel_unix_new().
Returns : | the file descriptor of the GIOChannel.

### g_io_channel_init ()

    void        g_io_channel_init               (GIOChannel *channel);

Initializes a GIOChannel struct. This is called by each of the above functions when creating a GIOChannel, and so is not often needed by the application programmer (unless you are creating a new type of GIOChannel).

`channel` : | a GIOChannel.

### g_io_channel_new_file ()

    GIOChannel* g_io_channel_new_file           (const gchar *filename,
                                                 const gchar *mode,
                                                 GError **error);

Open a file `filename` as a GIOChannel using mode `mode`. This channel will be closed when the last reference to it is dropped, so there is no need to call g_io_channel_close() (though doing so will not cause problems, as long as no attempt is made to access the channel after it is closed).

`filename` : | A string containing the name of a file.
`mode` : | One of "r", "w", "a", "r+", "w+", "a+". These have the same meaning as in `fopen()`.
`error` : | A location to return an error of type `G_FILE_ERROR`.
Returns : | A GIOChannel on success, `NULL` on failure.

### g_io_channel_read_chars ()

    GIOStatus   g_io_channel_read_chars         (GIOChannel *channel,
                                                 gchar *buf,
                                                 gsize count,
                                                 gsize *bytes_read,
                                                 GError **error);

Replacement for g_io_channel_read() with the new API.

`channel` : | a GIOChannel
`buf` : | a buffer to read data into
`count` : | the size of the buffer. Note that the buffer may not be complelely filled even if there is data in the buffer if the remaining data is not a complete character.
`bytes_read` : | The number of bytes read. This may be zero even on success if count < 6 and the channel's encoding is non-`NULL`. This indicates that the next UTF-8 character is too wide for the buffer.
`error` : | A location to return an error of type GConvertError or GIOChannelError.
Returns : | the status of the operation.

### g_io_channel_read_unichar ()

    GIOStatus   g_io_channel_read_unichar       (GIOChannel *channel,
                                                 gunichar *thechar,
                                                 GError **error);

This function cannot be called on a channel with `NULL` encoding.

`channel` : | a GIOChannel
`thechar` : | a location to return a character
`error` : | A location to return an error of type GConvertError or GIOChannelError
Returns : | a GIOStatus

### g_io_channel_read_line ()

    GIOStatus   g_io_channel_read_line          (GIOChannel *channel,
                                                 gchar **str_return,
                                                 gsize *length,
                                                 gsize *terminator_pos,
                                                 GError **error);

Reads a line, including the terminating character(s), from a GIOChannel into a newly-allocated string. `length` will contain allocated memory if the return is `G_IO_STATUS_NORMAL`.

`channel` : | a GIOChannel
`str_return` : | The line read from the GIOChannel, not including the line terminator. This data should be freed with g_free() when no longer needed. This is a nul-terminated string. If a `length` of zero is returned, this will be `NULL` instead.
`length` : | location to store length of the read data, or `NULL`
`terminator_pos` : | location to store position of line terminator, or `NULL`
`error` : | A location to return an error of type GConvertError or GIOChannelError
Returns : | a newly-allocated string. Free this string with g_free() when you are done with it.

### g_io_channel_read_line_string ()

    GIOStatus   g_io_channel_read_line_string   (GIOChannel *channel,
                                                 GString *buffer,
                                                 gsize *terminator_pos,
                                                 GError **error);

Reads a line from a GIOChannel, using a GString as a buffer.

`channel` : | a GIOChannel
`buffer` : | a GString into which the line will be written. If `buffer` already contains data, the old data will be overwritten.
`terminator_pos` : | location to store position of line terminator, or `NULL`
`error` : | a location to store an error of type GConvertError or GIOChannelError
Returns : | the status of the operation.

### g_io_channel_read_to_end ()

    GIOStatus   g_io_channel_read_to_end        (GIOChannel *channel,
                                                 gchar **str_return,
                                                 gsize *length,
                                                 GError **error);

Reads all the remaining data from the file.

Return value: `G_IO_STATUS_NORMAL` on success. This function never

`channel` : | a GIOChannel
`str_return` : | Location to store a pointer to a string holding the remaining data in the GIOChannel. This data should be freed with g_free() when no longer needed. This data is terminated by an extra nul character, but there may be other nuls in the intervening data.
`length` : | Location to store length of the data
`error` : | A location to return an error of type GConvertError or GIOChannelError
Returns : | `G_IO_STATUS_EOF`.

### g_io_channel_write_chars ()

    GIOStatus   g_io_channel_write_chars        (GIOChannel *channel,
                                                 const gchar *buf,
                                                 gssize count,
                                                 gsize *bytes_written,
                                                 GError **error);

Replacement for g_io_channel_write() with the new API.

On seekable channels with encodings other than `NULL` or UTF-8, generic mixing of reading and writing is not allowed. A call to g_io_channel_write_chars() may only be made on a channel from which data has been read in the cases described in the documentation for g_io_channel_set_encoding().

`channel` : | a GIOChannel
`buf` : | a buffer to write data from
`count` : | the size of the buffer. If -1, the buffer is taken to be a nul-terminated string.
`bytes_written` : | The number of bytes written. This can be nonzero even if the return value is not `G_IO_STATUS_NORMAL`. If the return value is `G_IO_STATUS_NORMAL` and the channel is blocking, this will always be equal to `count` if `count` >= 0.
`error` : | A location to return an error of type GConvertError or GIOChannelError
Returns : | the status of the operation.

### g_io_channel_write_unichar ()

    GIOStatus   g_io_channel_write_unichar      (GIOChannel *channel,
                                                 gunichar thechar,
                                                 GError **error);

This function cannot be called on a channel with `NULL` encoding.

`channel` : | a GIOChannel
`thechar` : | a character
`error` : | A location to return an error of type GConvertError or GIOChannelError
Returns : | a GIOStatus

### g_io_channel_flush ()

    GIOStatus   g_io_channel_flush              (GIOChannel *channel,
                                                 GError **error);

Flushes the write buffer for the GIOChannel.

`channel` : | a GIOChannel
`error` : | location to store an error of type GIOChannelError
Returns : | the status of the operation: One of G_IO_CHANNEL_NORMAL, G_IO_CHANNEL_AGAIN, or G_IO_CHANNEL_ERROR.

### g_io_channel_seek_position ()

    GIOStatus   g_io_channel_seek_position      (GIOChannel *channel,
                                                 gint64 offset,
                                                 GSeekType type,
                                                 GError **error);

Replacement for g_io_channel_seek() with the new API.

`channel` : | a GIOChannel
`offset` : | The offset in bytes from the position specified by `type`
`type` : | a GSeekType. The type `G_SEEK_CUR` is only allowed in those cases where a call to g_io_channel_set_encoding() is allowed. See the documentation for g_io_channel_set_encoding() for details.
`error` : | A location to return an error of type GIOChannelError
Returns : | the status of the operation.

### enum GSeekType

    typedef enum
    {
      G_SEEK_CUR,
      G_SEEK_SET,
      G_SEEK_END
    } GSeekType;

An enumeration specifying the base position for a g_io_channel_seek_position() operation.

`G_SEEK_CUR` | the current position in the file.
`G_SEEK_SET` | the start of the file.
`G_SEEK_END` | the end of the file.

### g_io_channel_shutdown ()

    GIOStatus   g_io_channel_shutdown           (GIOChannel *channel,
                                                 gboolean flush,
                                                 GError **err);

Close an IO channel. Any pending data to be written will be flushed if `flush` is `TRUE`. The channel will not be freed until the last reference is dropped using g_io_channel_unref().

`channel` : | a GIOChannel
`flush` : | if `TRUE`, flush pending
`err` : | location to store a GIOChannelError
Returns : | the status of the operation.

### enum GIOStatus

    typedef enum
    {
      G_IO_STATUS_ERROR,
      G_IO_STATUS_NORMAL,
      G_IO_STATUS_EOF,
      G_IO_STATUS_AGAIN
    } GIOStatus;

Stati returned by most of the GIOFuncs functions.

`G_IO_STATUS_ERROR` | An error occurred.
`G_IO_STATUS_NORMAL` | Success.
`G_IO_STATUS_EOF` | End of file.
`G_IO_STATUS_AGAIN` | Resource temporarily unavailable.

### enum GIOChannelError

    typedef enum
    {
      /* Derived from errno */
      G_IO_CHANNEL_ERROR_FBIG,
      G_IO_CHANNEL_ERROR_INVAL,
      G_IO_CHANNEL_ERROR_IO,
      G_IO_CHANNEL_ERROR_ISDIR,
      G_IO_CHANNEL_ERROR_NOSPC,
      G_IO_CHANNEL_ERROR_NXIO,
      G_IO_CHANNEL_ERROR_OVERFLOW,
      G_IO_CHANNEL_ERROR_PIPE,
      /* Other */
      G_IO_CHANNEL_ERROR_FAILED
    } GIOChannelError;

Error codes returned by GIOChannel operations.

`G_IO_CHANNEL_ERROR_FBIG` | File too large.
`G_IO_CHANNEL_ERROR_INVAL` | Invalid argument.
`G_IO_CHANNEL_ERROR_IO` | IO error.
`G_IO_CHANNEL_ERROR_ISDIR` | File is a directory.
`G_IO_CHANNEL_ERROR_NOSPC` | No space left on device.
`G_IO_CHANNEL_ERROR_NXIO` | No such device or address.
`G_IO_CHANNEL_ERROR_OVERFLOW` | Value too large for defined datatype.
`G_IO_CHANNEL_ERROR_PIPE` | Broken pipe.
`G_IO_CHANNEL_ERROR_FAILED` | Some other error.

### G_IO_CHANNEL_ERROR

    #define G_IO_CHANNEL_ERROR g_io_channel_error_quark()

Error domain for GIOChannel operations. Errors in this domain will be from the GIOChannelError enumeration. See GError for information on error domains.

### g_io_channel_error_from_errno ()

    GIOChannelError g_io_channel_error_from_errno
                                                (gint en);

Converts an `errno` error number to a GIOChannelError.

`en` : | an `errno` error number, e.g. `EINVAL`.
Returns : | a GIOChannelError error number, e.g. `G_IO_CHANNEL_ERROR_INVAL`.

### g_io_channel_ref ()

    void        g_io_channel_ref                (GIOChannel *channel);

Increments the reference count of a GIOChannel.

`channel` : | a GIOChannel.

### g_io_channel_unref ()

    void        g_io_channel_unref              (GIOChannel *channel);

Decrements the reference count of a GIOChannel.

`channel` : | a GIOChannel.

### g_io_create_watch ()

    GSource*    g_io_create_watch               (GIOChannel *channel,
                                                 GIOCondition condition);

Creates a GSource that's dispatched when `condition` is met for the given `channel`. For example, if condition is G_IO_IN, the source will be dispatched when there's data available for reading. g_io_add_watch() is a simpler interface to this same functionality, for the case where you want to add the source to the default main loop at the default priority.

`channel` : | a GIOChannel to watch
`condition` : | conditions to watch for
Returns : | a new GSource

### g_io_add_watch ()

    guint       g_io_add_watch                  (GIOChannel *channel,
                                                 GIOCondition condition,
                                                 GIOFunc func,
                                                 gpointer user_data);

Adds the GIOChannel into the main event loop with the default priority.

`channel` : | a GIOChannel.
`condition` : | the condition to watch for.
`func` : | the function to call when the condition is satisfied.
`user_data` : | user data to pass to `func`.
Returns : | the event source id.

### g_io_add_watch_full ()

    guint       g_io_add_watch_full             (GIOChannel *channel,
                                                 gint priority,
                                                 GIOCondition condition,
                                                 GIOFunc func,
                                                 gpointer user_data,
                                                 GDestroyNotify notify);

Adds the GIOChannel into the main event loop with the given priority.

`channel` : | a GIOChannel.
`priority` : | the priority of the GIOChannel source.
`condition` : | the condition to watch for.
`func` : | the function to call when the condition is satisfied.
`user_data` : | user data to pass to `func`.
`notify` : | the function to call when the source is removed.
Returns : | the event source id.

### enum GIOCondition

    typedef enum
    {
      G_IO_IN	GLIB_SYSDEF_POLLIN,
      G_IO_OUT	GLIB_SYSDEF_POLLOUT,
      G_IO_PRI	GLIB_SYSDEF_POLLPRI,
      G_IO_ERR	GLIB_SYSDEF_POLLERR,
      G_IO_HUP	GLIB_SYSDEF_POLLHUP,
      G_IO_NVAL	GLIB_SYSDEF_POLLNVAL
    } GIOCondition;

A bitwise combination representing a condition to watch for on an event source.

`G_IO_IN` | There is data to read.
`G_IO_OUT` | Data can be written (without blocking).
`G_IO_PRI` | There is urgent data to read.
`G_IO_ERR` | Error condition.
`G_IO_HUP` | Hung up (the connection has been broken, usually for pipes and sockets).
`G_IO_NVAL` | Invalid request. The file descriptor is not open.

### GIOFunc ()

    gboolean    (*GIOFunc)                      (GIOChannel *source,
                                                 GIOCondition condition,
                                                 gpointer data);

Specifies the type of function passed to g_io_add_watch() or g_io_add_watch_full(), which is called when the requested condition on a GIOChannel is satisfied.

`source` : | the GIOChannel event source.
`condition` : | the condition which has been satisfied.
`data` : | user data set in g_io_add_watch() or g_io_add_watch_full().
Returns : | the function should return `FALSE` if the event source should be removed.

### struct GIOFuncs

    struct GIOFuncs
    {
      GIOStatus (*io_read)           (GIOChannel   *channel,
    			          gchar        *buf,
    				  gsize         count,
    				  gsize        *bytes_read,
    				  GError      **err);
      GIOStatus (*io_write)          (GIOChannel   *channel,
    				  const gchar  *buf,
    				  gsize         count,
    				  gsize        *bytes_written,
    				  GError      **err);
      GIOStatus (*io_seek)           (GIOChannel   *channel,
    				  gint64        offset,
    				  GSeekType     type,
    				  GError      **err);
      GIOStatus  (*io_close)         (GIOChannel   *channel,
    				  GError      **err);
      GSource*   (*io_create_watch)  (GIOChannel   *channel,
    				  GIOCondition  condition);
      void       (*io_free)          (GIOChannel   *channel);
      GIOStatus  (*io_set_flags)     (GIOChannel   *channel,
                                      GIOFlags      flags,
    				  GError      **err);
      GIOFlags   (*io_get_flags)     (GIOChannel   *channel);
    };

A table of functions used to handle different types of GIOChannel in a generic way.

### g_io_channel_get_buffer_size ()

    gsize       g_io_channel_get_buffer_size    (GIOChannel *channel);

Gets the buffer size.

`channel` : | a GIOChannel
Returns : | the size of the buffer.

### g_io_channel_set_buffer_size ()

    void        g_io_channel_set_buffer_size    (GIOChannel *channel,
                                                 gsize size);

Sets the buffer size.

`channel` : | a GIOChannel
`size` : | the size of the buffer. 0 == pick a good size

### g_io_channel_get_buffer_condition ()

    GIOCondition g_io_channel_get_buffer_condition
                                                (GIOChannel *channel);

This function returns a GIOCondition depending on whether there is data to be read/space to write data in the internal buffers in the GIOChannel. Only the flags `G_IO_IN` and `G_IO_OUT` may be set.

`channel` : | A GIOChannel
Returns : | A GIOCondition

### g_io_channel_get_flags ()

    GIOFlags    g_io_channel_get_flags          (GIOChannel *channel);

Gets the current flags for a GIOChannel, including read-only flags such as `G_IO_FLAG_IS_READABLE`.

The values of the flags `G_IO_FLAG_IS_READABLE` and `G_IO_FLAG_IS_WRITEABLE` are cached for internal use by the channel when it is created. If they should change at some later point (e.g. partial shutdown of a socket with the UNIX `shutdown()` function), the user should immediately call g_io_channel_get_flags() to update the internal values of these flags.

`channel` : | a GIOChannel
Returns : | the flags which are set on the channel

### g_io_channel_set_flags ()

    GIOStatus   g_io_channel_set_flags          (GIOChannel *channel,
                                                 GIOFlags flags,
                                                 GError **error);

Sets the (writeable) flags in `channel` to (`flags` & `G_IO_CHANNEL_SET_MASK`).

`channel` : | a GIOChannel.
`flags` : | the flags to set on the IO channel.
`error` : | A location to return an error of type GIOChannelError.
Returns : | the status of the operation.

### enum GIOFlags

    typedef enum
    {
      G_IO_FLAG_APPEND = 1 << 0,
      G_IO_FLAG_NONBLOCK = 1 << 1,
      G_IO_FLAG_IS_READABLE = 1 << 2,	/* Read only flag */
      G_IO_FLAG_IS_WRITEABLE = 1 << 3,	/* Read only flag */
      G_IO_FLAG_IS_SEEKABLE = 1 << 4,	/* Read only flag */
      G_IO_FLAG_MASK = (1 << 5) - 1,
      G_IO_FLAG_GET_MASK = G_IO_FLAG_MASK,
      G_IO_FLAG_SET_MASK = G_IO_FLAG_APPEND | G_IO_FLAG_NONBLOCK
    } GIOFlags;

Specifies properties of a GIOChannel. Some of the flags can only be read with g_io_channel_get_flags(), but not changed with g_io_channel_set_flags().

`G_IO_FLAG_APPEND` | turns on append mode, corresponds to `O_APPEND` (see the documentation of the UNIX `open()` syscall).
`G_IO_FLAG_NONBLOCK` | turns on nonblocking mode, corresponds to `O_NONBLOCK`/`O_NDELAY` (see the documentation of the UNIX `open()` syscall).
`G_IO_FLAG_IS_READABLE` | indicates that the io channel is readable. This flag can not be changed.
`G_IO_FLAG_IS_WRITEABLE` | indicates that the io channel is writable. This flag can not be changed.
`G_IO_FLAG_IS_SEEKABLE` | indicates that the io channel is seekable, i.e. that g_io_channel_seek_position() can be used on it. This flag can not be changed.
`G_IO_FLAG_MASK` |
`G_IO_FLAG_GET_MASK` |
`G_IO_FLAG_SET_MASK` |

### g_io_channel_get_line_term ()

    G_CONST_RETURN gchar* g_io_channel_get_line_term
                                                (GIOChannel *channel,
                                                 gint *length);

This returns the string that GIOChannel uses to determine where in the file a line break occurs. A value of `NULL` indicates auto detection.

`channel` : | a GIOChannel
`length` : | a location to return the length of the line terminator
Returns : | The line termination string. This value is owned by GLib and must not be freed.

### g_io_channel_set_line_term ()

    void        g_io_channel_set_line_term      (GIOChannel *channel,
                                                 const gchar *line_term,
                                                 gint length);

This sets the string that GIOChannel uses to determine where in the file a line break occurs.

`channel` : | a GIOChannel
`line_term` : | The line termination string. Use `NULL` for auto detect. Auto detection breaks on "\n", "\r\n", "\r", "\0", and the Unicode paragraph separator. Auto detection should not be used for anything other than file-based channels.
`length` : | The length of the termination string. If -1 is passed, the string is assumed to be nul-terminated. This option allows termination strings with embeded nuls.

### g_io_channel_get_buffered ()

    gboolean    g_io_channel_get_buffered       (GIOChannel *channel);

Returns whether `channel` is buffered.

`channel` : | a GIOChannel.
Returns : | `TRUE` if the `channel` is buffered.

### g_io_channel_set_buffered ()

    void        g_io_channel_set_buffered       (GIOChannel *channel,
                                                 gboolean buffered);

The buffering state can only be set if the channel's encoding is `NULL`. For any other encoding, the channel must be buffered.

A buffered channel can only be set unbuffered if the channel's internal buffers have been flushed. Newly created channels or channels which have returned `G_IO_STATUS_EOF` not require such a flush. For write-only channels, a call to g_io_channel_flush() is sufficient. For all other channels, the buffers may be flushed by a call to g_io_channel_seek_position(). This includes the possibility of seeking with seek type `G_SEEK_CUR` and an offset of zero. Note that this means that socket-based channels cannot be set unbuffered once they have had data read from them.

On unbuffered channels, it is safe to mix read and write calls from the new and old APIs, if this is necessary for maintaining old code.

The default state of the channel is buffered.

`channel` : | a GIOChannel
`buffered` : | whether to set the channel buffered or unbuffered

### g_io_channel_get_encoding ()

    G_CONST_RETURN gchar* g_io_channel_get_encoding
                                                (GIOChannel *channel);

Gets the encoding for the input/output of the channel. The internal encoding is always UTF-8. The encoding `NULL` makes the channel safe for binary data.

`channel` : | a GIOChannel
Returns : | A string containing the encoding, this string is owned by GLib and must not be freed.

### g_io_channel_set_encoding ()

    GIOStatus   g_io_channel_set_encoding       (GIOChannel *channel,
                                                 const gchar *encoding,
                                                 GError **error);

Sets the encoding for the input/output of the channel. The internal encoding is always UTF-8. The default encoding for the external file is UTF-8.

The encoding `NULL` is safe to use with binary data.

The encoding can only be set under the following conditions:

1. The channel was just created, and has not been written to or read from yet.

2. The channel is write-only.

3. The channel is a file, and the file pointer was just repositioned by a call to g_io_channel_seek_position(). (This flushes all the internal buffers.)

4. The current encoding is `NULL` or UTF-8.

5. One of the (new API) read functions has just returned `G_IO_STATUS_EOF` (or, in the case of g_io_channel_read_to_end(), `G_IO_STATUS_NORMAL`).

6. One of the functions g_io_channel_read_chars() or g_io_channel_read_unichar() has returned `G_IO_STATUS_AGAIN` or `G_IO_STATUS_ERROR`. This may be useful in the case of `G_CONVERT_ERROR_ILLEGAL_SEQUENCE`. Returning one of these statuses from g_io_channel_read_line(), g_io_channel_read_line_string(), or g_io_channel_read_to_end() does not guarantee that the encoding can be changed.

Channels which do not meet the above conditions cannot call g_io_channel_seek_position() with an offset of `G_SEEK_CUR`, and if they are "seekable" cannot call g_io_channel_write_chars() after calling one of the API "read" functions.

`channel` : | a GIOChannel
`encoding` : | the encoding type
`error` : | location to store an error of type GConvertError.
Returns : | `G_IO_STATUS_NORMAL` if the encoding was successfully set.

### g_io_channel_get_close_on_unref ()

    gboolean    g_io_channel_get_close_on_unref (GIOChannel *channel);

Returns whether the file/socket/whatever associated with `channel` will be closed when `channel` receives its final unref and is destroyed. The default value of this is `TRUE` for channels created by g_io_channel_new_file(), and `FALSE` for all other channels.

`channel` : | a GIOChannel.
Returns : | Whether the channel will be closed on the final unref of the GIOChannel data structure.

### g_io_channel_set_close_on_unref ()

    void        g_io_channel_set_close_on_unref (GIOChannel *channel,
                                                 gboolean do_close);

Setting this flag to `TRUE` for a channel you have already closed can cause problems.

`channel` : | a GIOChannel
`do_close` : | Whether to close the channel on the final unref of the GIOChannel data structure. The default value of this is `TRUE` for channels created by g_io_channel_new_file(), and `FALSE` for all other channels.

### g_io_channel_read ()

    GIOError    g_io_channel_read               (GIOChannel *channel,
                                                 gchar *buf,
                                                 gsize count,
                                                 gsize *bytes_read);

Warning
`g_io_channel_read` is deprecated and should not be used in newly-written code.

Reads data from a GIOChannel. This function is deprecated. New code should use g_io_channel_read_chars() instead.

`channel` : | a GIOChannel.
`buf` : | a buffer to read the data into (which should be at least count bytes long).
`count` : | the number of bytes to read from the GIOChannel.
`bytes_read` : | returns the number of bytes actually read.
Returns : | `G_IO_ERROR_NONE` if the operation was successful.

### enum GIOError

    typedef enum
    {
      G_IO_ERROR_NONE,
      G_IO_ERROR_AGAIN,
      G_IO_ERROR_INVAL,
      G_IO_ERROR_UNKNOWN
    } GIOError;

GIOError is only used by the deprecated functions g_io_channel_read(), g_io_channel_write(), and g_io_channel_seek().

### g_io_channel_write ()

    GIOError    g_io_channel_write              (GIOChannel *channel,
                                                 const gchar *buf,
                                                 gsize count,
                                                 gsize *bytes_written);

Warning
`g_io_channel_write` is deprecated and should not be used in newly-written code.

Writes data to a GIOChannel. This function is deprecated. New code should use g_io_channel_write_chars() instead.

`channel` : | a GIOChannel.
`buf` : | the buffer containing the data to write.
`count` : | the number of bytes to write.
`bytes_written` : | the number of bytes actually written.
Returns : | `G_IO_ERROR_NONE` if the operation was successful.

### g_io_channel_seek ()

    GIOError    g_io_channel_seek               (GIOChannel *channel,
                                                 gint64 offset,
                                                 GSeekType type);

Warning
`g_io_channel_seek` is deprecated and should not be used in newly-written code.

Sets the current position in the GIOChannel, similar to the standard library function `fseek()`. This function is deprecated. New code should use g_io_channel_seek_position() instead.

`channel` : | a GIOChannel.
`offset` : | an offset, in bytes, which is added to the position specified by `type`
`type` : | the position in the file, which can be `G_SEEK_CUR` (the current position), `G_SEEK_SET` (the start of the file), or `G_SEEK_END` (the end of the file).
Returns : | `G_IO_ERROR_NONE` if the operation was successful.

### g_io_channel_close ()

    void        g_io_channel_close              (GIOChannel *channel);

Warning
`g_io_channel_close` is deprecated and should not be used in newly-written code.

Close an IO channel. Any pending data to be written will be flushed, ignoring errors. The channel will not be freed until the last reference is dropped using g_io_channel_unref(). This function is deprecated: you should use g_io_channel_shutdown() instead.

`channel` : | A GIOChannel

## See Also

gtk_input_add_full(), gtk_input_remove(), gdk_input_add(), gdk_input_add_full(), gdk_input_remove()

  Convenience functions for creating GIOChannel instances and adding them to the main event loop.

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