File Name Encodings

Historically, UNIX has not had a defined encoding for file names: a file name is valid as long as it does not have path separators in it ("/"). However, displaying file names may require conversion: from the character set in which they were created, to the character set in which the application operates. Consider the Spanish file name "Presentación.sxi". If the application which created it uses ISO-8859-1 for its encoding,

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Character:  P  r  e  s  e  n  t  a  c  i  ó  n  .  s  x  i
Hex code:   50 72 65 73 65 6e 74 61 63 69 f3 6e 2e 73 78 69

However, if the application use UTF-8, the actual file name on disk would look like this:

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Character:  P  r  e  s  e  n  t  a  c  i  ó     n  .  s  x  i
Hex code:   50 72 65 73 65 6e 74 61 63 69 c3 b3 6e 2e 73 78 69

Glib uses UTF-8 for its strings, and GUI toolkits like GTK+ that use GLib do the same thing. If you get a file name from the file system, for example, from readdir() or from g_dir_read_name(), and you wish to display the file name to the user, you will need to convert it into UTF-8. The opposite case is when the user types the name of a file they wish to save: the toolkit will give you that string in UTF-8 encoding, and you will need to convert it to the character set used for file names before you can create the file with open() or fopen().

By default, GLib assumes that file names on disk are in UTF-8 encoding. This is a valid assumption for file systems which were created relatively recently: most applications use UTF-8 encoding for their strings, and that is also what they use for the file names they create. However, older file systems may still contain file names created in "older" encodings, such as ISO-8859-1. In this case, for compatibility reasons, you may want to instruct GLib to use that particular encoding for file names rather than UTF-8. You can do this by specifying the encoding for file names in the G_FILENAME_ENCODING environment variable. For example, if your installation uses ISO-8859-1 for file names, you can put this in your ~/.profile:

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export G_FILENAME_ENCODING=ISO-8859-1

GLib provides the functions g_filename_to_utf8() and g_filename_from_utf8() to perform the necessary conversions. These functions convert file names from the encoding specified in G_FILENAME_ENCODING to UTF-8 and vice-versa. This diagram illustrates how these functions are used to convert between UTF-8 and the encoding for file names in the file system.

Conversion between file name encodings # {file-name-encodings-diagram)

Checklist for Application Writers

This section is a practical summary of the detailed things to do to make sure your applications process file name encodings correctly.

g_convert ()

gchar *
g_convert (const gchar *str,
           gssize len,
           const gchar *to_codeset,
           const gchar *from_codeset,
           gsize *bytes_read,
           gsize *bytes_written,
           GError **error);

Converts a string from one character set to another.

Note that you should use g_iconv() for streaming conversions. Despite the fact that bytes_read can return information about partial characters, the g_convert_... functions are not generally suitable for streaming. If the underlying converter maintains internal state, then this won't be preserved across successive calls to g_convert(), g_convert_with_iconv() or g_convert_with_fallback(). (An example of this is the GNU C converter for CP1255 which does not emit a base character until it knows that the next character is not a mark that could combine with the base character.)

Using extensions such as "//TRANSLIT" may not work (or may not work well) on many platforms. Consider using g_str_to_ascii() instead.

g_convert_with_fallback ()

gchar *
g_convert_with_fallback (const gchar *str,
                         gssize len,
                         const gchar *to_codeset,
                         const gchar *from_codeset,
                         const gchar *fallback,
                         gsize *bytes_read,
                         gsize *bytes_written,
                         GError **error);

Converts a string from one character set to another, possibly including fallback sequences for characters not representable in the output. Note that it is not guaranteed that the specification for the fallback sequences in fallback will be honored. Some systems may do an approximate conversion from from_codeset to to_codeset in their iconv() functions, in which case GLib will simply return that approximate conversion.

Note that you should use g_iconv() for streaming conversions. Despite the fact that bytes_read can return information about partial characters, the g_convert_... functions are not generally suitable for streaming. If the underlying converter maintains internal state, then this won't be preserved across successive calls to g_convert(), g_convert_with_iconv() or g_convert_with_fallback(). (An example of this is the GNU C converter for CP1255 which does not emit a base character until it knows that the next character is not a mark that could combine with the base character.)

g_convert_with_iconv ()

gchar *
g_convert_with_iconv (const gchar *str,
                      gssize len,
                      GIConv converter,
                      gsize *bytes_read,
                      gsize *bytes_written,
                      GError **error);

Converts a string from one character set to another.

Note that you should use g_iconv() for streaming conversions. Despite the fact that bytes_read can return information about partial characters, the g_convert_... functions are not generally suitable for streaming. If the underlying converter maintains internal state, then this won't be preserved across successive calls to g_convert(), g_convert_with_iconv() or g_convert_with_fallback(). (An example of this is the GNU C converter for CP1255 which does not emit a base character until it knows that the next character is not a mark that could combine with the base character.)

Characters which are valid in the input character set, but which have no representation in the output character set will result in a G_CONVERT_ERROR_ILLEGAL_SEQUENCE error. This is in contrast to the iconv() specification, which leaves this behaviour implementation defined. Note that this is the same error code as is returned for an invalid byte sequence in the input character set. To get defined behaviour for conversion of unrepresentable characters, use g_convert_with_fallback().

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g_iconv_open ()

GIConv
g_iconv_open (const gchar *to_codeset,
              const gchar *from_codeset);

Same as the standard UNIX routine iconv_open(), but may be implemented via libiconv on UNIX flavors that lack a native implementation.

GLib provides g_convert() and g_locale_to_utf8() which are likely more convenient than the raw iconv wrappers.

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g_iconv ()

gsize
g_iconv (GIConv converter,
         gchar **inbuf,
         gsize *inbytes_left,
         gchar **outbuf,
         gsize *outbytes_left);

Same as the standard UNIX routine iconv(), but may be implemented via libiconv on UNIX flavors that lack a native implementation.

GLib provides g_convert() and g_locale_to_utf8() which are likely more convenient than the raw iconv wrappers.

Note that the behaviour of iconv() for characters which are valid in the input character set, but which have no representation in the output character set, is implementation defined. This function may return success (with a positive number of non-reversible conversions as replacement characters were used), or it may return -1 and set an error such as EILSEQ, in such a situation.

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g_iconv_close ()

gint
g_iconv_close (GIConv converter);

Same as the standard UNIX routine iconv_close(), but may be implemented via libiconv on UNIX flavors that lack a native implementation. Should be called to clean up the conversion descriptor from g_iconv_open() when you are done converting things.

GLib provides g_convert() and g_locale_to_utf8() which are likely more convenient than the raw iconv wrappers.

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g_locale_to_utf8 ()

gchar *
g_locale_to_utf8 (const gchar *opsysstring,
                  gssize len,
                  gsize *bytes_read,
                  gsize *bytes_written,
                  GError **error);

Converts a string which is in the encoding used for strings by the C runtime (usually the same as that used by the operating system) in the current locale into a UTF-8 string.

If the source encoding is not UTF-8 and the conversion output contains a nul character, the error G_CONVERT_ERROR_EMBEDDED_NUL is set and the function returns NULL. If the source encoding is UTF-8, an embedded nul character is treated with the G_CONVERT_ERROR_ILLEGAL_SEQUENCE error for backward compatibility with earlier versions of this library. Use g_convert() to produce output that may contain embedded nul characters.

g_filename_to_utf8 ()

gchar *
g_filename_to_utf8 (const gchar *opsysstring,
                    gssize len,
                    gsize *bytes_read,
                    gsize *bytes_written,
                    GError **error);

Converts a string which is in the encoding used by GLib for filenames into a UTF-8 string. Note that on Windows GLib uses UTF-8 for filenames; on other platforms, this function indirectly depends on the current locale.

The input string shall not contain nul characters even if the len argument is positive. A nul character found inside the string will result in error G_CONVERT_ERROR_ILLEGAL_SEQUENCE. If the source encoding is not UTF-8 and the conversion output contains a nul character, the error G_CONVERT_ERROR_EMBEDDED_NUL is set and the function returns NULL. Use g_convert() to produce output that may contain embedded nul characters.

g_filename_from_utf8 ()

gchar *
g_filename_from_utf8 (const gchar *utf8string,
                      gssize len,
                      gsize *bytes_read,
                      gsize *bytes_written,
                      GError **error);

Converts a string from UTF-8 to the encoding GLib uses for filenames. Note that on Windows GLib uses UTF-8 for filenames; on other platforms, this function indirectly depends on the current locale.

The input string shall not contain nul characters even if the len argument is positive. A nul character found inside the string will result in error G_CONVERT_ERROR_ILLEGAL_SEQUENCE. If the filename encoding is not UTF-8 and the conversion output contains a nul character, the error G_CONVERT_ERROR_EMBEDDED_NUL is set and the function returns NULL.

g_get_filename_charsets ()

gboolean
g_get_filename_charsets (const gchar ***charsets);

Determines the preferred character sets used for filenames. The first character set from the charsets is the filename encoding, the subsequent character sets are used when trying to generate a displayable representation of a filename, see g_filename_display_name().

On Unix, the character sets are determined by consulting the environment variables G_FILENAME_ENCODING and G_BROKEN_FILENAMES. On Windows, the character set used in the GLib API is always UTF-8 and said environment variables have no effect.

G_FILENAME_ENCODING may be set to a comma-separated list of character set names. The special token "@locale" is taken to mean the character set for the current locale. If G_FILENAME_ENCODING is not set, but G_BROKEN_FILENAMES is, the character set of the current locale is taken as the filename encoding. If neither environment variable is set, UTF-8 is taken as the filename encoding, but the character set of the current locale is also put in the list of encodings.

The returned charsets belong to GLib and must not be freed.

Note that on Unix, regardless of the locale character set or G_FILENAME_ENCODING value, the actual file names present on a system might be in any random encoding or just gibberish.

Since: 2.6

g_filename_display_name ()

gchar *
g_filename_display_name (const gchar *filename);

Converts a filename into a valid UTF-8 string. The conversion is not necessarily reversible, so you should keep the original around and use the return value of this function only for display purposes. Unlike g_filename_to_utf8(), the result is guaranteed to be non-NULL even if the filename actually isn't in the GLib file name encoding.

If GLib cannot make sense of the encoding of filename , as a last resort it replaces unknown characters with U+FFFD, the Unicode replacement character. You can search the result for the UTF-8 encoding of this character (which is "\357\277\275" in octal notation) to find out if filename was in an invalid encoding.

If you know the whole pathname of the file you should use g_filename_display_basename(), since that allows location-based translation of filenames.

Since: 2.6

g_filename_display_basename ()

gchar *
g_filename_display_basename (const gchar *filename);

Returns the display basename for the particular filename, guaranteed to be valid UTF-8. The display name might not be identical to the filename, for instance there might be problems converting it to UTF-8, and some files can be translated in the display.

If GLib cannot make sense of the encoding of filename , as a last resort it replaces unknown characters with U+FFFD, the Unicode replacement character. You can search the result for the UTF-8 encoding of this character (which is "\357\277\275" in octal notation) to find out if filename was in an invalid encoding.

You must pass the whole absolute pathname to this functions so that translation of well known locations can be done.

This function is preferred over g_filename_display_name() if you know the whole path, as it allows translation.

Since: 2.6

g_locale_from_utf8 ()

gchar *
g_locale_from_utf8 (const gchar *utf8string,
                    gssize len,
                    gsize *bytes_read,
                    gsize *bytes_written,
                    GError **error);

Converts a string from UTF-8 to the encoding used for strings by the C runtime (usually the same as that used by the operating system) in the current locale. On Windows this means the system codepage.

The input string shall not contain nul characters even if the len argument is positive. A nul character found inside the string will result in error G_CONVERT_ERROR_ILLEGAL_SEQUENCE. Use g_convert() to convert input that may contain embedded nul characters.

g_get_charset ()

gboolean
g_get_charset (const char **charset);

Obtains the character set for the current locale; you might use this character set as an argument to g_convert(), to convert from the current locale's encoding to some other encoding. (Frequently g_locale_to_utf8() and g_locale_from_utf8() are nice shortcuts, though.)

On Windows the character set returned by this function is the so-called system default ANSI code-page. That is the character set used by the "narrow" versions of C library and Win32 functions that handle file names. It might be different from the character set used by the C library's current locale.

On Linux, the character set is found by consulting nl_langinfo() if available. If not, the environment variables LC_ALL, LC_CTYPE, LANG and CHARSET are queried in order.

The return value is TRUE if the locale's encoding is UTF-8, in that case you can perhaps avoid calling g_convert().

The string returned in charset is not allocated, and should not be freed.

g_get_codeset ()

gchar *
g_get_codeset (void);

Gets the character set for the current locale.

GIConv

typedef struct _GIConv *GIConv;

The GIConv struct wraps an iconv() conversion descriptor. It contains private data and should only be accessed using the following functions.

G_CONVERT_ERROR

#define G_CONVERT_ERROR g_convert_error_quark()

Error domain for character set conversions. Errors in this domain will be from the GConvertError enumeration. See GError for information on error domains.

enum GConvertError

Error codes returned by character set conversion routines.