File Utilities

File Utilities — various file-related functions.

Synopsis


#include <glib.h>
#include <glib/gstdio.h>


enum        GFileError;
#define     G_FILE_ERROR
enum        GFileTest;
GFileError  g_file_error_from_errno         (gint err_no);
gboolean    g_file_get_contents             (const gchar *filename,
                                             gchar **contents,
                                             gsize *length,
                                             GError **error);
gboolean    g_file_test                     (const gchar *filename,
                                             GFileTest test);
gint        g_mkstemp                       (gchar *tmpl);
gint        g_file_open_tmp                 (const gchar *tmpl,
                                             gchar **name_used,
                                             GError **error);
gchar*      g_file_read_link                (const gchar *filename,
                                             GError **error);

            GDir;
GDir*       g_dir_open                      (const gchar *path,
                                             guint flags,
                                             GError **error);
const gchar* g_dir_read_name                (GDir *dir);
void        g_dir_rewind                    (GDir *dir);
void        g_dir_close                     (GDir *dir);

int         g_open                          (const gchar *filename,
                                             int flags,
                                             int mode);
int         g_rename                        (const gchar *oldfilename,
                                             const gchar *newfilename);
int         g_mkdir                         (const gchar *filename,
                                             int mode);
int         g_stat                          (const gchar *filename,
                                             struct stat *buf);
int         g_lstat                         (const gchar *filename,
                                             struct stat *buf);
int         g_unlink                        (const gchar *filename);
int         g_remove                        (const gchar *filename);
int         g_rmdir                         (const gchar *filename);
FILE*       g_fopen                         (const gchar *filename,
                                             const gchar *mode);
FILE*       g_freopen                       (const gchar *filename,
                                             const gchar *mode,
                                             FILE *stream);

Description

There is a group of functions which wrap the common POSIX functions dealing with filenames (g_open(), g_rename(), g_mkdir(), g_stat(), g_unlink(), g_remove(), g_fopen(), g_freopen()). The point of these wrappers is to make it possible to handle file names with any Unicode characters in them on Windows without having to use ifdefs and the wide character API in the application code.

The pathname argument should be in the GLib file name encoding. On POSIX this is the actual on-disk encoding which might correspond to the locale settings of the process (or the G_FILENAME_ENCODING environment variable), or not.

On Windows the GLib file name encoding is UTF-8. Note that the Microsoft C library does not use UTF-8, but has separate APIs for current system code page and wide characters (UTF-16). The GLib wrappers call the wide character API if present (on modern Windows systems), otherwise convert to/from the system code page.

Another group of functions allows to open and read directories in the GLib file name encoding. These are g_dir_open(), g_dir_read_name(), g_dir_rewind(), g_dir_close().

Details

enum GFileError

typedef enum
{
  G_FILE_ERROR_EXIST,
  G_FILE_ERROR_ISDIR,
  G_FILE_ERROR_ACCES,
  G_FILE_ERROR_NAMETOOLONG,
  G_FILE_ERROR_NOENT,
  G_FILE_ERROR_NOTDIR,
  G_FILE_ERROR_NXIO,
  G_FILE_ERROR_NODEV,
  G_FILE_ERROR_ROFS,
  G_FILE_ERROR_TXTBSY,
  G_FILE_ERROR_FAULT,
  G_FILE_ERROR_LOOP,
  G_FILE_ERROR_NOSPC,
  G_FILE_ERROR_NOMEM,
  G_FILE_ERROR_MFILE,
  G_FILE_ERROR_NFILE,
  G_FILE_ERROR_BADF,
  G_FILE_ERROR_INVAL,
  G_FILE_ERROR_PIPE,
  G_FILE_ERROR_AGAIN,
  G_FILE_ERROR_INTR,
  G_FILE_ERROR_IO,
  G_FILE_ERROR_PERM,
  G_FILE_ERROR_NOSYS,
  G_FILE_ERROR_FAILED
} GFileError;

Values corresponding to errno codes returned from file operations on UNIX. Unlike errno codes, GFileError values are available on all systems, even Windows. The exact meaning of each code depends on what sort of file operation you were performing; the UNIX documentation gives more details. The following error code descriptions come from the GNU C Library manual, and are under the copyright of that manual.

It's not very portable to make detailed assumptions about exactly which errors will be returned from a given operation. Some errors don't occur on some systems, etc., sometimes there are subtle differences in when a system will report a given error, etc.

G_FILE_ERROR_EXISTOperation not permitted; only the owner of the file (or other resource) or processes with special privileges can perform the operation.
G_FILE_ERROR_ISDIRFile is a directory; you cannot open a directory for writing, or create or remove hard links to it.
G_FILE_ERROR_ACCESPermission denied; the file permissions do not allow the attempted operation.
G_FILE_ERROR_NAMETOOLONGFilename too long.
G_FILE_ERROR_NOENTNo such file or directory. This is a "file doesn't exist" error for ordinary files that are referenced in contexts where they are expected to already exist.
G_FILE_ERROR_NOTDIRA file that isn't a directory was specified when a directory is required.
G_FILE_ERROR_NXIONo such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.
G_FILE_ERROR_NODEVThis file is of a type that doesn't support mapping.
G_FILE_ERROR_ROFSThe directory containing the new link can't be modified because it's on a read-only file system.
G_FILE_ERROR_TXTBSYText file busy.
G_FILE_ERROR_FAULTYou passed in a pointer to bad memory. (GLib won't reliably return this, don't pass in pointers to bad memory.)
G_FILE_ERROR_LOOPToo many levels of symbolic links were encountered in looking up a file name. This often indicates a cycle of symbolic links.
G_FILE_ERROR_NOSPCNo space left on device; write operation on a file failed because the disk is full.
G_FILE_ERROR_NOMEMNo memory available. The system cannot allocate more virtual memory because its capacity is full.
G_FILE_ERROR_MFILEThe current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.
G_FILE_ERROR_NFILEThere are too many distinct file openings in the entire system.
G_FILE_ERROR_BADFBad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).
G_FILE_ERROR_INVALInvalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.
G_FILE_ERROR_PIPEBroken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a `SIGPIPE' signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see this code unless it has handled or blocked `SIGPIPE'.
G_FILE_ERROR_AGAINResource temporarily unavailable; the call might work if you try again later.
G_FILE_ERROR_INTRInterrupted function call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.
G_FILE_ERROR_IOInput/output error; usually used for physical read or write errors. i.e. the disk or other physical device hardware is returning errors.
G_FILE_ERROR_PERMOperation not permitted; only the owner of the file (or other resource) or processes with special privileges can perform the operation.
G_FILE_ERROR_NOSYSFunction not implemented; this indicates that the system is missing some functionality.
G_FILE_ERROR_FAILEDDoes not correspond to a UNIX error code; this is the standard "failed for unspecified reason" error code present in all GError error code enumerations. Returned if no specific code applies.

G_FILE_ERROR

#define G_FILE_ERROR g_file_error_quark ()

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


enum GFileTest

typedef enum
{
  G_FILE_TEST_IS_REGULAR    = 1 << 0,
  G_FILE_TEST_IS_SYMLINK    = 1 << 1,
  G_FILE_TEST_IS_DIR        = 1 << 2,
  G_FILE_TEST_IS_EXECUTABLE = 1 << 3,
  G_FILE_TEST_EXISTS        = 1 << 4
} GFileTest;

A test to perform on a file using g_file_test().

G_FILE_TEST_IS_REGULARTRUE if the file is a regular file (not a symlink or directory)
G_FILE_TEST_IS_SYMLINKTRUE if the file is a symlink.
G_FILE_TEST_IS_DIRTRUE if the file is a directory.
G_FILE_TEST_IS_EXECUTABLETRUE if the file is executable.
G_FILE_TEST_EXISTSTRUE if the file exists. It may or may not be a regular file.

g_file_error_from_errno ()

GFileError  g_file_error_from_errno         (gint err_no);

Gets a GFileError constant based on the passed-in errno. For example, if you pass in EEXIST this function returns G_FILE_ERROR_EXIST. Unlike errno values, you can portably assume that all GFileError values will exist.

Normally a GFileError value goes into a GError returned from a function that manipulates files. So you would use g_file_error_from_errno() when constructing a GError.

err_no : an "errno" value
Returns : GFileError corresponding to the given errno

g_file_get_contents ()

gboolean    g_file_get_contents             (const gchar *filename,
                                             gchar **contents,
                                             gsize *length,
                                             GError **error);

Reads an entire file into allocated memory, with good error checking.

If the call was successful, it returns TRUE and sets contents to the file contents and length to the length of the file contents in bytes. The string stored in contents will be nul-terminated, so for text files you can pass NULL for the length argument. If the call was not successful, it returns FALSE and sets error. The error domain is G_FILE_ERROR. Possible error codes are those in the GFileError enumeration. In the error case, contents is set to NULL and length is set to zero.

filename : name of a file to read contents from, in the GLib file name encoding
contents : location to store an allocated string
length : location to store length in bytes of the contents, or NULL
error : return location for a GError, or NULL
Returns : TRUE on success, FALSE if an error occurred

g_file_test ()

gboolean    g_file_test                     (const gchar *filename,
                                             GFileTest test);

Returns TRUE if any of the tests in the bitfield test are TRUE. For example, (G_FILE_TEST_EXISTS | G_FILE_TEST_IS_DIR) will return TRUE if the file exists; the check whether it's a directory doesn't matter since the existence test is TRUE. With the current set of available tests, there's no point passing in more than one test at a time.

Apart from G_FILE_TEST_IS_SYMLINK all tests follow symbolic links, so for a symbolic link to a regular file g_file_test() will return TRUE for both G_FILE_TEST_IS_SYMLINK and G_FILE_TEST_IS_REGULAR.

Note, that for a dangling symbolic link g_file_test() will return TRUE for G_FILE_TEST_IS_SYMLINK and FALSE for all other flags.

You should never use g_file_test() to test whether it is safe to perform an operation, because there is always the possibility of the condition changing before you actually perform the operation. For example, you might think you could use G_FILE_TEST_IS_SYMLINK to know whether it is is safe to write to a file without being tricked into writing into a different location. It doesn't work!

/* DON'T DO THIS */
 if (!g_file_test (filename, G_FILE_TEST_IS_SYMLINK)) {
   fd = g_open (filename, O_WRONLY);
   /* write to fd */
 }

Another thing to note is that G_FILE_TEST_EXISTS and G_FILE_TEST_IS_EXECUTABLE are implemented using the access() system call. This usually doesn't matter, but if your program is setuid or setgid it means that these tests will give you the answer for the real user ID and group ID, rather than the effective user ID and group ID.

On Windows, there are no symlinks, so testing for G_FILE_TEST_IS_SYMLINK will always return FALSE. Testing for G_FILE_TEST_IS_EXECUTABLE will just check that the file exists and its name indicates that it is executable, checking for well-known extensions and those listed in the PATHEXT environment variable.

filename : a filename to test in the GLib file name encoding
test : bitfield of GFileTest flags
Returns : whether a test was TRUE

g_mkstemp ()

gint        g_mkstemp                       (gchar *tmpl);

Opens a temporary file. See the mkstemp() documentation on most UNIX-like systems. This is a portability wrapper, which simply calls mkstemp() on systems that have it, and implements it in GLib otherwise.

The parameter is a string that should match the rules for mkstemp(), i.e. end in "XXXXXX". The X string will be modified to form the name of a file that didn't exist. The string should be in the GLib file name encoding. Most importantly, on Windows it should be in UTF-8.

tmpl : template filename
Returns : A file handle (as from open()) to the file opened for reading and writing. The file is opened in binary mode on platforms where there is a difference. The file handle should be closed with close(). In case of errors, -1 is returned.

g_file_open_tmp ()

gint        g_file_open_tmp                 (const gchar *tmpl,
                                             gchar **name_used,
                                             GError **error);

Opens a file for writing in the preferred directory for temporary files (as returned by g_get_tmp_dir()).

tmpl should be a string in the GLib file name encoding ending with six 'X' characters, as the parameter to g_mkstemp() (or mkstemp()). However, unlike these functions, the template should only be a basename, no directory components are allowed. If template is NULL, a default template is used.

Note that in contrast to g_mkstemp() (and mkstemp()) tmpl is not modified, and might thus be a read-only literal string.

The actual name used is returned in name_used if non-NULL. This string should be freed with g_free() when not needed any longer. The returned name is in the GLib file name encoding.

tmpl : Template for file name, as in g_mkstemp(), basename only
name_used : location to store actual name used
error : return location for a GError
Returns : A file handle (as from open()) to the file opened for reading and writing. The file is opened in binary mode on platforms where there is a difference. The file handle should be closed with close(). In case of errors, -1 is returned and error will be set.

g_file_read_link ()

gchar*      g_file_read_link                (const gchar *filename,
                                             GError **error);

Reads the contents of the symbolic link filename like the POSIX readlink() function. The returned string is in the encoding used for filenames. Use g_filename_to_utf8() to convert it to UTF-8.

filename : the symbolic link
error : return location for a GError
Returns : A newly allocated string with the contents of the symbolic link, or NULL if an error occurred.

Since 2.4


GDir

typedef struct _GDir GDir;

An opaque structure representing an opened directory.


g_dir_open ()

GDir*       g_dir_open                      (const gchar *path,
                                             guint flags,
                                             GError **error);

Opens a directory for reading. The names of the files in the directory can then be retrieved using g_dir_read_name().

path : the path to the directory you are interested in. On Unix in the on-disk encoding. On Windows in UTF-8
flags : Currently must be set to 0. Reserved for future use.
error : return location for a GError, or NULL. If non-NULL, an error will be set if and only if g_dir_open_fails.
Returns : a newly allocated GDir on success, NULL on failure. If non-NULL, you must free the result with g_dir_close() when you are finished with it.

g_dir_read_name ()

const gchar* g_dir_read_name                (GDir *dir);

Retrieves the name of the next entry in the directory. The '.' and '..' entries are omitted. On Windows, the returned name is in UTF-8. On Unix, it is in the on-disk encoding.

dir : a GDir* created by g_dir_open()
Returns : The entry's name or NULL if there are no more entries. The return value is owned by GLib and must not be modified or freed.

g_dir_rewind ()

void        g_dir_rewind                    (GDir *dir);

Resets the given directory. The next call to g_dir_read_name() will return the first entry again.

dir : a GDir* created by g_dir_open()

g_dir_close ()

void        g_dir_close                     (GDir *dir);

Closes the directory and deallocates all related resources.

dir : a GDir* created by g_dir_open()

g_open ()

int         g_open                          (const gchar *filename,
                                             int flags,
                                             int mode);

A wrapper for the POSIX open() function. The open() function is used to convert a pathname into a file descriptor. Note that on POSIX systems file descriptors are implemented by the operating system. On Windows, it's the C library that implements open() and file descriptors. The actual Windows API for opening files is something different.

See the C library manual for more details about open().

filename : a pathname in the GLib file name encoding
flags : as in open()
mode : as in open()
Returns : a new file descriptor, or -1 if an error occurred. The return value can be used exactly like the return value from open().

Since 2.6


g_rename ()

int         g_rename                        (const gchar *oldfilename,
                                             const gchar *newfilename);

A wrapper for the POSIX rename() function. The rename() function renames a file, moving it between directories if required.

See your C library manual for more details about how rename() works on your system. Note in particular that on Windows, it is in general not possible to rename a file if a file with the new name already exists. Also it is not possible in general to rename an open file.

oldfilename : a pathname in the GLib file name encoding
newfilename : a pathname in the GLib file name encoding
Returns : 0 if the renaming succeeded, -1 if an error occurred

Since 2.6


g_mkdir ()

int         g_mkdir                         (const gchar *filename,
                                             int mode);

A wrapper for the POSIX mkdir() function. The mkdir() function attempts to create a directory with the given name and permissions.

See the C library manual for more details about mkdir().

filename : a pathname in the GLib file name encoding
mode : permissions to use for the newly created directory
Returns : 0 if the directory was successfully created, -1 if an error occurred

Since 2.6


g_stat ()

int         g_stat                          (const gchar *filename,
                                             struct stat *buf);

A wrapper for the POSIX stat() function. The stat() function returns information about a file.

See the C library manual for more details about stat().

filename : a pathname in the GLib file name encoding
buf : a pointer to a stat struct, which will be filled with the file information
Returns : 0 if the information was successfully retrieved, -1 if an error occurred

Since 2.6


g_lstat ()

int         g_lstat                         (const gchar *filename,
                                             struct stat *buf);

A wrapper for the POSIX lstat() function. The lstat() function is like stat() except that in the case of symbolic links, it returns information about the symbolic link itself and not the file that it refers to. If the system does not support symbolic links g_lstat() is identical to g_stat().

See the C library manual for more details about lstat().

filename : a pathname in the GLib file name encoding
buf : a pointer to a stat struct, which will be filled with the file information
Returns : 0 if the information was successfully retrieved, -1 if an error occurred

Since 2.6


g_unlink ()

int         g_unlink                        (const gchar *filename);

A wrapper for the POSIX unlink() function. The unlink() function deletes a name from the filesystem. If this was the last link to the file and no processes have it opened, the diskspace occupied by the file is freed.

See your C library manual for more details about unlink(). Note that on Windows, it is in general not possible to delete files that are open to some process, or mapped into memory.

filename : a pathname in the GLib file name encoding
Returns : 0 if the name was successfully deleted, -1 if an error occurred

Since 2.6


g_remove ()

int         g_remove                        (const gchar *filename);

A wrapper for the POSIX remove() function. The remove() function deletes a name from the filesystem.

See your C library manual for more details about how remove() works on your system. On Unix, remove() removes also directories, as it calls unlink() for files and rmdir() for directories. On Windows, although remove() in the C library only works for files, this function tries first remove() and then if that fails rmdir(), and thus works for both files and directories. Note however, that on Windows, it is in general not possible to remove a file that is open to some process, or mapped into memory.

filename : a pathname in the GLib file name encoding
Returns : 0 if the file was successfully removed, -1 if an error occurred

Since 2.6


g_rmdir ()

int         g_rmdir                         (const gchar *filename);

A wrapper for the POSIX rmdir() function. The rmdir() function deletes a directory from the filesystem.

See your C library manual for more details about how rmdir() works on your system.

filename : a pathname in the GLib file name encoding
Returns : 0 if the directory was successfully removed, -1 if an error occurred

Since 2.6


g_fopen ()

FILE*       g_fopen                         (const gchar *filename,
                                             const gchar *mode);

A wrapper for the POSIX fopen() function. The fopen() function opens a file and associates a new stream with it.

See the C library manual for more details about fopen().

filename : a pathname in the GLib file name encoding
mode : a string describing the mode in which the file should be opened
Returns : A <typename>FILE</typename> pointer if the file was successfully opened, or NULL if an error occurred

Since 2.6


g_freopen ()

FILE*       g_freopen                       (const gchar *filename,
                                             const gchar *mode,
                                             FILE *stream);

A wrapper for the POSIX freopen() function. The freopen() function opens a file and associates it with an existing stream.

See the C library manual for more details about freopen().

filename : a pathname in the GLib file name encoding
mode : a string describing the mode in which the file should be opened
stream : an existing stream which will be reused, or NULL
Returns : A <typename>FILE</typename> pointer if the file was successfully opened, or NULL if an error occurred.

Since 2.6