## Miscellaneous Utility Functions

Miscellaneous Utility Functions — a selection of portable utility functions

## Synopsis

    #include <glib.h>

    const gchar*        g_get_application_name              (void);
    void                g_set_application_name              (const gchar *application_name);
    gchar*              g_get_prgname                       (void);
    void                g_set_prgname                       (const gchar *prgname);
    const gchar*        g_getenv                            (const gchar *variable);
    gboolean            g_setenv                            (const gchar *variable,
                                                             const gchar *value,
                                                             gboolean overwrite);
    void                g_unsetenv                          (const gchar *variable);
    gchar**             g_listenv                           (void);
    const gchar*        g_get_user_name                     (void);
    const gchar*        g_get_real_name                     (void);
    const gchar*        g_get_user_cache_dir                (void);
    const gchar*        g_get_user_data_dir                 (void);
    const gchar*        g_get_user_config_dir               (void);
    enum                GUserDirectory;
    const gchar*        g_get_user_special_dir              (GUserDirectory directory);
    const gchar* const * g_get_system_data_dirs             (void);
    const gchar* const * g_get_system_config_dirs           (void);

    const gchar*        g_get_host_name                     (void);
    const gchar*        g_get_home_dir                      (void);
    const gchar*        g_get_tmp_dir                       (void);
    gchar*              g_get_current_dir                   (void);
    const gchar*        g_basename                          (const gchar *file_name);
    #define             g_dirname
    gboolean            g_path_is_absolute                  (const gchar *file_name);
    const gchar*        g_path_skip_root                    (const gchar *file_name);
    gchar*              g_path_get_basename                 (const gchar *file_name);
    gchar*              g_path_get_dirname                  (const gchar *file_name);
    gchar *             g_build_filename                    (const gchar *first_element,
                                                             ...);
    gchar *             g_build_filenamev                   (gchar **args);
    gchar *             g_build_path                        (const gchar *separator,
                                                             const gchar *first_element,
                                                             ...);
    gchar *             g_build_pathv                       (const gchar *separator,
                                                             gchar **args);
    char *              g_format_size_for_display           (goffset size);

    gchar*              g_find_program_in_path              (const gchar *program);

    gint                g_bit_nth_lsf                       (gulong mask,
                                                             gint nth_bit);
    gint                g_bit_nth_msf                       (gulong mask,
                                                             gint nth_bit);
    guint               g_bit_storage                       (gulong number);

    guint               g_spaced_primes_closest             (guint num);

    void                g_atexit                            (GVoidFunc func);

    guint               g_parse_debug_string                (const gchar *string,
                                                             const GDebugKey *keys,
                                                             guint nkeys);
                        GDebugKey;

    void                (*GVoidFunc)                        (void);
    void                (*GFreeFunc)                        (gpointer data);

    void                g_qsort_with_data                   (gconstpointer pbase,
                                                             gint total_elems,
                                                             gsize size,
                                                             GCompareDataFunc compare_func,
                                                             gpointer user_data);

    void                g_nullify_pointer                   (gpointer *nullify_location);

## Description

These are portable utility functions.

## Details

### g_get_application_name ()

    const gchar*        g_get_application_name              (void);

Gets a human-readable name for the application, as set by `g_set_application_name()`. This name should be localized if possible, and is intended for display to the user. Contrast with `g_get_prgname()`, which gets a non-localized name. If `g_set_application_name()` has not been called, returns the result of `g_get_prgname()` (which may be `NULL` if `g_set_prgname()` has also not been called).

Returns : | human-readable application name. may return `NULL`

Since 2.2

### g_set_application_name ()

    void                g_set_application_name              (const gchar *application_name);

Sets a human-readable name for the application. This name should be localized if possible, and is intended for display to the user. Contrast with `g_set_prgname()`, which sets a non-localized name. `g_set_prgname()` will be called automatically by `gtk_init()`, but `g_set_application_name()` will not.

Note that for thread safety reasons, this function can only be called once.

The application name will be used in contexts such as error messages, or when displaying an application's name in the task list.

`application_name` : | localized name of the application

Since 2.2

### g_get_prgname ()

    gchar*              g_get_prgname                       (void);

Gets the name of the program. This name should not be localized, contrast with `g_get_application_name()`. (If you are using GDK or GTK+ the program name is set in `gdk_init()`, which is called by `gtk_init()`. The program name is found by taking the last component of `argv[0]`.)

Returns : | the name of the program. The returned string belongs to GLib and must not be modified or freed.

### g_set_prgname ()

    void                g_set_prgname                       (const gchar *prgname);

Sets the name of the program. This name should not be localized, contrast with `g_set_application_name()`. Note that for thread-safety reasons this function can only be called once.

`prgname` : | the name of the program.

### g_getenv ()

    const gchar*        g_getenv                            (const gchar *variable);

Returns the value of an environment variable. The name and value are in the GLib file name encoding. On UNIX, this means the actual bytes which might or might not be in some consistent character set and encoding. On Windows, it is in UTF-8. On Windows, in case the environment variable's value contains references to other environment variables, they are expanded.

`variable` : | the environment variable to get, in the GLib file name encoding.
Returns : | the value of the environment variable, or `NULL` if the environment variable is not found. The returned string may be overwritten by the next call to `g_getenv()`, `g_setenv()` or `g_unsetenv()`.

### g_setenv ()

    gboolean            g_setenv                            (const gchar *variable,
                                                             const gchar *value,
                                                             gboolean overwrite);

Sets an environment variable. Both the variable's name and value should be in the GLib file name encoding. On UNIX, this means that they can be any sequence of bytes. On Windows, they should be in UTF-8.

Note that on some systems, when variables are overwritten, the memory used for the previous variables and its value isn't reclaimed.

`variable` : | the environment variable to set, must not contain '='.
`value` : | the value for to set the variable to.
`overwrite` : | whether to change the variable if it already exists.
Returns : | `FALSE` if the environment variable couldn't be set.

Since 2.4

### g_unsetenv ()

    void                g_unsetenv                          (const gchar *variable);

Removes an environment variable from the environment.

Note that on some systems, when variables are overwritten, the memory used for the previous variables and its value isn't reclaimed. Furthermore, this function can't be guaranteed to operate in a threadsafe way.

`variable` : | the environment variable to remove, must not contain '='.

Since 2.4

### g_listenv ()

    gchar**             g_listenv                           (void);

Gets the names of all variables set in the environment.

Returns :

a `NULL`-terminated list of strings which must be freed with `g_strfreev()`. Programs that want to be portable to Windows should typically use this function and `g_getenv()` instead of using the environ array from the C library directly. On Windows, the strings in the environ array are in system codepage encoding, while in most of the typical use cases for environment variables in GLib-using programs you want the UTF-8 encoding that this function and `g_getenv()` provide.

Since 2.8

### g_get_user_name ()

    const gchar*        g_get_user_name                     (void);

Gets the user name of the current user. The encoding of the returned string is system-defined. On UNIX, it might be the preferred file name encoding, or something else, and there is no guarantee that it is even consistent on a machine. On Windows, it is always UTF-8.

Returns : | the user name of the current user.

### g_get_real_name ()

    const gchar*        g_get_real_name                     (void);

Gets the real name of the user. This usually comes from the user's entry in the `passwd` file. The encoding of the returned string is system-defined. (On Windows, it is, however, always UTF-8.) If the real user name cannot be determined, the string "Unknown" is returned.

Returns : | the user's real name.

### g_get_user_cache_dir ()

    const gchar*        g_get_user_cache_dir                (void);

Returns a base directory in which to store non-essential, cached data specific to particular user.

On UNIX platforms this is determined using the mechanisms described in the XDG Base Directory Specification

Returns : | a string owned by GLib that must not be modified or freed.

Since 2.6

### g_get_user_data_dir ()

    const gchar*        g_get_user_data_dir                 (void);

Returns a base directory in which to access application data such as icons that is customized for a particular user.

On UNIX platforms this is determined using the mechanisms described in the XDG Base Directory Specification

Returns : | a string owned by GLib that must not be modified or freed.

Since 2.6

### g_get_user_config_dir ()

    const gchar*        g_get_user_config_dir               (void);

Returns a base directory in which to store user-specific application configuration information such as user preferences and settings.

On UNIX platforms this is determined using the mechanisms described in the XDG Base Directory Specification

Returns : | a string owned by GLib that must not be modified or freed.

Since 2.6

### enum GUserDirectory

    typedef enum {
      G_USER_DIRECTORY_DESKTOP,
      G_USER_DIRECTORY_DOCUMENTS,
      G_USER_DIRECTORY_DOWNLOAD,
      G_USER_DIRECTORY_MUSIC,
      G_USER_DIRECTORY_PICTURES,
      G_USER_DIRECTORY_PUBLIC_SHARE,
      G_USER_DIRECTORY_TEMPLATES,
      G_USER_DIRECTORY_VIDEOS,

      G_USER_N_DIRECTORIES
    } GUserDirectory;

These are logical ids for special directories which are defined depending on the platform used. You should use `g_get_user_special_dir()` to retrieve the full path associated to the logical id.

The GUserDirectory enumeration can be extended at later date. Not every platform has a directory for every logical id in this enumeration.

`G_USER_DIRECTORY_DESKTOP` | the user's Desktop directory
`G_USER_DIRECTORY_DOCUMENTS` | the user's Documents directory
`G_USER_DIRECTORY_DOWNLOAD` | the user's Downloads directory
`G_USER_DIRECTORY_MUSIC` | the user's Music directory
`G_USER_DIRECTORY_PICTURES` | the user's Pictures directory
`G_USER_DIRECTORY_PUBLIC_SHARE` | the user's shared directory
`G_USER_DIRECTORY_TEMPLATES` | the user's Templates directory
`G_USER_DIRECTORY_VIDEOS` | the user's Movies directory
`G_USER_N_DIRECTORIES` | the number of enum values

Since 2.14

### g_get_user_special_dir ()

    const gchar*        g_get_user_special_dir              (GUserDirectory directory);

Returns the full path of a special directory using its logical id.

On Unix this is done using the XDG special user directories. For compatibility with existing practise, `G_USER_DIRECTORY_DESKTOP` falls back to `$HOME/Desktop` when XDG special user directories have not been set up.

Depending on the platform, the user might be able to change the path of the special directory without requiring the session to restart; GLib will not reflect any change once the special directories are loaded.

`directory` : | the logical id of special directory
Returns : | the path to the specified special directory, or `NULL` if the logical id was not found. The returned string is owned by GLib and should not be modified or freed.

Since 2.14

### g_get_system_data_dirs ()

    const gchar* const * g_get_system_data_dirs             (void);

Returns an ordered list of base directories in which to access system-wide application data.

On UNIX platforms this is determined using the mechanisms described in the XDG Base Directory Specification

On Windows the first elements in the list are the Application Data and Documents folders for All Users. (These can be determined only on Windows 2000 or later and are not present in the list on other Windows versions.) See documentation for CSIDL_COMMON_APPDATA and CSIDL_COMMON_DOCUMENTS.

Then follows the "share" subfolder in the installation folder for the package containing the DLL that calls this function, if it can be determined.

Finally the list contains the "share" subfolder in the installation folder for GLib, and in the installation folder for the package the application's .exe file belongs to.

The installation folders above are determined by looking up the folder where the module (DLL or EXE) in question is located. If the folder's name is "bin", its parent is used, otherwise the folder itself.

Note that on Windows the returned list can vary depending on where this function is called.

Returns : | a `NULL`-terminated array of strings owned by GLib that must not be modified or freed.

Since 2.6

### g_get_system_config_dirs ()

    const gchar* const * g_get_system_config_dirs           (void);

Returns an ordered list of base directories in which to access system-wide configuration information.

On UNIX platforms this is determined using the mechanisms described in the XDG Base Directory Specification

Returns : | a `NULL`-terminated array of strings owned by GLib that must not be modified or freed.

Since 2.6

### g_get_host_name ()

    const gchar*        g_get_host_name                     (void);

Return a name for the machine.

The returned name is not necessarily a fully-qualified domain name, or even present in DNS or some other name service at all. It need not even be unique on your local network or site, but usually it is. Callers should not rely on the return value having any specific properties like uniqueness for security purposes. Even if the name of the machine is changed while an application is running, the return value from this function does not change. The returned string is owned by GLib and should not be modified or freed. If no name can be determined, a default fixed string "localhost" is returned.

Returns : | the host name of the machine.

Since 2.8

### g_get_home_dir ()

    const gchar*        g_get_home_dir                      (void);

Gets the current user's home directory as defined in the password database.

Note that in contrast to traditional UNIX tools, this function prefers `passwd` entries over the `HOME` environment variable.

One of the reasons for this decision is that applications in many cases need special handling to deal with the case where `HOME` is

Not owned by the user
Not writeable
Not even readable

Since applications are in general not written to deal with these situations it was considered better to make `g_get_home_dir()` not pay attention to `HOME` and to return the real home directory for the user. If applications want to pay attention to `HOME`, they can do:

     const char *homedir = g_getenv ("HOME");
      if (!homedir)
         homedir = g_get_home_dir ();

Returns : | the current user's home directory

### g_get_tmp_dir ()

    const gchar*        g_get_tmp_dir                       (void);

Gets the directory to use for temporary files. This is found from inspecting the environment variables `TMPDIR`, `TMP`, and `TEMP` in that order. If none of those are defined "/tmp" is returned on UNIX and "C:\" on Windows. The encoding of the returned string is system-defined. On Windows, it is always UTF-8. The return value is never `NULL`.

Returns : | the directory to use for temporary files.

### g_get_current_dir ()

    gchar*              g_get_current_dir                   (void);

Gets the current directory. The returned string should be freed when no longer needed. The encoding of the returned string is system defined. On Windows, it is always UTF-8.

Returns : | the current directory.

### g_basename ()

    const gchar*        g_basename                          (const gchar *file_name);

### Warning

`g_basename` has been deprecated since version 2.2 and should not be used in newly-written code. Use `g_path_get_basename()` instead, but notice that `g_path_get_basename()` allocates new memory for the returned string, unlike this function which returns a pointer into the argument.

Gets the name of the file without any leading directory components. It returns a pointer into the given file name string.

`file_name` : | the name of the file.
Returns : | the name of the file without any leading directory components.

### g_dirname

    #define             g_dirname

### Warning

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

This function is deprecated and will be removed in the next major release of GLib. Use `g_path_get_dirname()` instead.

Gets the directory components of a file name. If the file name has no directory components "." is returned. The returned string should be freed when no longer needed.

Returns : | the directory components of the file.

### g_path_is_absolute ()

    gboolean            g_path_is_absolute                  (const gchar *file_name);

Returns `TRUE` if the given `file_name` is an absolute file name, i.e. it contains a full path from the root directory such as "/usr/local" on UNIX or "C:\windows" on Windows systems.

`file_name` : | a file name.
Returns : | `TRUE` if `file_name` is an absolute path.

### g_path_skip_root ()

    const gchar*        g_path_skip_root                    (const gchar *file_name);

Returns a pointer into `file_name` after the root component, i.e. after the "/" in UNIX or "C:\" under Windows. If `file_name` is not an absolute path it returns `NULL`.

`file_name` : | a file name.
Returns : | a pointer into `file_name` after the root component.

### g_path_get_basename ()

    gchar*              g_path_get_basename                 (const gchar *file_name);

Gets the last component of the filename. If `file_name` ends with a directory separator it gets the component before the last slash. If `file_name` consists only of directory separators (and on Windows, possibly a drive letter), a single separator is returned. If `file_name` is empty, it gets ".".

`file_name` : | the name of the file.
Returns : | a newly allocated string containing the last component of the filename.

### g_path_get_dirname ()

    gchar*              g_path_get_dirname                  (const gchar *file_name);

Gets the directory components of a file name. If the file name has no directory components "." is returned. The returned string should be freed when no longer needed.

`file_name` : | the name of the file.
Returns : | the directory components of the file.

### g_build_filename ()

    gchar *             g_build_filename                    (const gchar *first_element,
                                                             ...);

Creates a filename from a series of elements using the correct separator for filenames.

On Unix, this function behaves identically to `g_build_path (G_DIR_SEPARATOR_S, first_element, ....)`.

On Windows, it takes into account that either the backslash (`\` or slash (`/`) can be used as separator in filenames, but otherwise behaves as on Unix. When file pathname separators need to be inserted, the one that last previously occurred in the parameters (reading from left to right) is used.

No attempt is made to force the resulting filename to be an absolute path. If the first element is a relative path, the result will be a relative path.

`first_element` : | the first element in the path
`...` : | remaining elements in path, terminated by `NULL`
Returns : | a newly-allocated string that must be freed with `g_free()`.

### g_build_filenamev ()

    gchar *             g_build_filenamev                   (gchar **args);

Behaves exactly like `g_build_filename()`, but takes the path elements as a string array, instead of varargs. This function is mainly meant for language bindings.

`args` : | `NULL`-terminated array of strings containing the path elements.
Returns : | a newly-allocated string that must be freed with `g_free()`.

Since 2.8

### g_build_path ()

    gchar *             g_build_path                        (const gchar *separator,
                                                             const gchar *first_element,
                                                             ...);

Creates a path from a series of elements using `separator` as the separator between elements. At the boundary between two elements, any trailing occurrences of separator in the first element, or leading occurrences of separator in the second element are removed and exactly one copy of the separator is inserted.

Empty elements are ignored.

The number of leading copies of the separator on the result is the same as the number of leading copies of the separator on the first non-empty element.

The number of trailing copies of the separator on the result is the same as the number of trailing copies of the separator on the last non-empty element. (Determination of the number of trailing copies is done without stripping leading copies, so if the separator is `ABA`, `ABABA` has 1 trailing copy.)

However, if there is only a single non-empty element, and there are no characters in that element not part of the leading or trailing separators, then the result is exactly the original value of that element.

Other than for determination of the number of leading and trailing copies of the separator, elements consisting only of copies of the separator are ignored.

`separator` : | a string used to separator the elements of the path.
`first_element` : | the first element in the path
`...` : | remaining elements in path, terminated by `NULL`
Returns : | a newly-allocated string that must be freed with `g_free()`.

### g_build_pathv ()

    gchar *             g_build_pathv                       (const gchar *separator,
                                                             gchar **args);

Behaves exactly like `g_build_path()`, but takes the path elements as a string array, instead of varargs. This function is mainly meant for language bindings.

`separator` : | a string used to separator the elements of the path.
`args` : | `NULL`-terminated array of strings containing the path elements.
Returns : | a newly-allocated string that must be freed with `g_free()`.

Since 2.8

### g_format_size_for_display ()

    char *              g_format_size_for_display           (goffset size);

Formats a size (for example the size of a file) into a human readable string. Sizes are rounded to the nearest size prefix (KB, MB, GB) and are displayed rounded to the nearest tenth. E.g. the file size 3292528 bytes will be converted into the string "3.1 MB".

The prefix units base is 1024 (i.e. 1 KB is 1024 bytes).

`size` : | a size in bytes.
Returns : | a formatted string containing a human readable file size.

Since 2.16

### g_find_program_in_path ()

    gchar*              g_find_program_in_path              (const gchar *program);

Locates the first executable named `program` in the user's path, in the same way that `execvp()` would locate it. Returns an allocated string with the absolute path name, or `NULL` if the program is not found in the path. If `program` is already an absolute path, returns a copy of `program` if `program` exists and is executable, and `NULL` otherwise. On Windows, if `program` does not have a file type suffix, tries with the suffixes .exe, .cmd, .bat and .com, and the suffixes in the `PATHEXT` environment variable.

On Windows, it looks for the file in the same way as `CreateProcess()` would. This means first in the directory where the executing program was loaded from, then in the current directory, then in the Windows 32-bit system directory, then in the Windows directory, and finally in the directories in the `PATH` environment variable. If the program is found, the return value contains the full name including the type suffix.

`program` : | a program name in the GLib file name encoding
Returns : | absolute path, or `NULL`

### g_bit_nth_lsf ()

    gint                g_bit_nth_lsf                       (gulong mask,
                                                             gint nth_bit);

Find the position of the first bit set in `mask`, searching from (but not including) `nth_bit` upwards. Bits are numbered from 0 (least significant) to sizeof(gulong) * 8 - 1 (31 or 63, usually). To start searching from the 0th bit, set `nth_bit` to -1.

`mask` : | a gulong containing flags.
`nth_bit` : | the index of the bit to start the search from.
Returns : | the index of the first bit set which is higher than `nth_bit`.

### g_bit_nth_msf ()

    gint                g_bit_nth_msf                       (gulong mask,
                                                             gint nth_bit);

Find the position of the first bit set in `mask`, searching from (but not including) `nth_bit` downwards. Bits are numbered from 0 (least significant) to sizeof(gulong) * 8 - 1 (31 or 63, usually). To start searching from the last bit, set `nth_bit` to -1 or GLIB_SIZEOF_LONG * 8.

`mask` : | a gulong containing flags.
`nth_bit` : | the index of the bit to start the search from.
Returns : | the index of the first bit set which is lower than `nth_bit`.

### g_bit_storage ()

    guint               g_bit_storage                       (gulong number);

Gets the number of bits used to hold `number`, e.g. if `number` is 4, 3 bits are needed.

`number` : | a guint.
Returns : | the number of bits used to hold `number`.

### g_spaced_primes_closest ()

    guint               g_spaced_primes_closest             (guint num);

Gets the smallest prime number from a built-in array of primes which is larger than `num`. This is used within GLib to calculate the optimum size of a GHashTable.

The built-in array of primes ranges from 11 to 13845163 such that each prime is approximately 1.5-2 times the previous prime.

`num` : | a guint.
Returns : | the smallest prime number from a built-in array of primes which is larger than `num`.

### g_atexit ()

    void                g_atexit                            (GVoidFunc func);

Specifies a function to be called at normal program termination.

Since GLib 2.8.2, on Windows `g_atexit()` actually is a preprocessor macro that maps to a call to the `atexit()` function in the C library. This means that in case the code that calls `g_atexit()`, i.e. `atexit()`, is in a DLL, the function will be called when the DLL is detached from the program. This typically makes more sense than that the function is called when the GLib DLL is detached, which happened earlier when `g_atexit()` was a function in the GLib DLL.

The behaviour of `atexit()` in the context of dynamically loaded modules is not formally specified and varies wildly.

On POSIX systems, calling `g_atexit()` (or `atexit()`) in a dynamically loaded module which is unloaded before the program terminates might well cause a crash at program exit.

Some POSIX systems implement `atexit()` like Windows, and have each dynamically loaded module maintain an own atexit chain that is called when the module is unloaded.

On other POSIX systems, before a dynamically loaded module is unloaded, the registered atexit functions (if any) residing in that module are called, regardless where the code that registered them resided. This is presumably the most robust approach.

As can be seen from the above, for portability it's best to avoid calling `g_atexit()` (or `atexit()`) except in the main executable of a program.

`func` : | the function to call on normal program termination.

### g_parse_debug_string ()

    guint               g_parse_debug_string                (const gchar *string,
                                                             const GDebugKey *keys,
                                                             guint nkeys);

Parses a string containing debugging options into a `guint` containing bit flags. This is used within GDK and GTK+ to parse the debug options passed on the command line or through environment variables.

`string` : | a list of debug options separated by colons, spaces, or commas; or the string "all" to set all flags, or `NULL`.
`keys` : | pointer to an array of GDebugKey which associate strings with bit flags.
`nkeys` : | the number of GDebugKeys in the array.
Returns : | the combined set of bit flags.

### GDebugKey

    typedef struct {
      gchar *key;
      guint	 value;
    } GDebugKey;

Associates a string with a bit flag. Used in `g_parse_debug_string()`.

gchar *`key`; | the string
guint `value`; | the flag

### GVoidFunc ()

    void                (*GVoidFunc)                        (void);

Declares a type of function which takes no arguments and has no return value. It is used to specify the type function passed to `g_atexit()`.

### GFreeFunc ()

    void                (*GFreeFunc)                        (gpointer data);

Declares a type of function which takes an arbitrary data pointer argument and has no return value. It is not currently used in GLib or GTK+.

`data` : | a data pointer.

### g_qsort_with_data ()

    void                g_qsort_with_data                   (gconstpointer pbase,
                                                             gint total_elems,
                                                             gsize size,
                                                             GCompareDataFunc compare_func,
                                                             gpointer user_data);

This is just like the standard C `qsort()` function, but the comparison routine accepts a user data argument.

`pbase` : | start of array to sort
`total_elems` : | elements in the array
`size` : | size of each element
`compare_func` : | function to compare elements
`user_data` : | data to pass to `compare_func`

### g_nullify_pointer ()

    void                g_nullify_pointer                   (gpointer *nullify_location);

Set the pointer at the specified location to `NULL`.

`nullify_location` : | the memory address of the pointer.