#### 10.2.1 Calling `glob`

The result of globbing is a vector of file names (strings). To return this vector, `glob` uses a special data type, `glob_t`, which is a structure. You pass `glob` the address of the structure, and it fills in the structure's fields to tell you about the results.

— Data Type: glob_t

> This data type holds a pointer to a word vector. More precisely, it records both the address of the word vector and its size. The GNU implementation contains some more fields which are non-standard extensions.

> `gl_pathc`
>   The number of elements in the vector, excluding the initial null entries if the GLOB_DOOFFS flag is used (see gl_offs below).
> `gl_pathv`
>   The address of the vector. This field has type `char **`.
> `gl_offs`
>   The offset of the first real element of the vector, from its nominal address in the `gl_pathv` field. Unlike the other fields, this is always an input to `glob`, rather than an output from it.

>   If you use a nonzero offset, then that many elements at the beginning of the vector are left empty. (The `glob` function fills them with null pointers.)

>   The `gl_offs` field is meaningful only if you use the `GLOB_DOOFFS` flag. Otherwise, the offset is always zero regardless of what is in this field, and the first real element comes at the beginning of the vector.

> `gl_closedir`
>   The address of an alternative implementation of the `closedir` function. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `void (*) (void *)`.

>   This is a GNU extension.

> `gl_readdir`
>   The address of an alternative implementation of the `readdir` function used to read the contents of a directory. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `struct dirent *(*) (void *)`.

>   This is a GNU extension.

> `gl_opendir`
>   The address of an alternative implementation of the `opendir` function. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `void *(*) (const char *)`.

>   This is a GNU extension.

> `gl_stat`
>   The address of an alternative implementation of the `stat` function to get information about an object in the filesystem. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `int (*) (const char *, struct stat *)`.

>   This is a GNU extension.

> `gl_lstat`
>   The address of an alternative implementation of the `lstat` function to get information about an object in the filesystems, not following symbolic links. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `int (*) (const char *, struct stat *)`.

>   This is a GNU extension.

> `gl_flags`
>   The flags used when `glob` was called. In addition, `GLOB_MAGCHAR` might be set. See Flags for Globbing for more details.

>   This is a GNU extension.

For use in the `glob64` function `glob.h` contains another definition for a very similar type. `glob64_t` differs from `glob_t` only in the types of the members `gl_readdir`, `gl_stat`, and `gl_lstat`.

— Data Type: glob64_t

> This data type holds a pointer to a word vector. More precisely, it records both the address of the word vector and its size. The GNU implementation contains some more fields which are non-standard extensions.

> `gl_pathc`
>   The number of elements in the vector, excluding the initial null entries if the GLOB_DOOFFS flag is used (see gl_offs below).
> `gl_pathv`
>   The address of the vector. This field has type `char **`.
> `gl_offs`
>   The offset of the first real element of the vector, from its nominal address in the `gl_pathv` field. Unlike the other fields, this is always an input to `glob`, rather than an output from it.

>   If you use a nonzero offset, then that many elements at the beginning of the vector are left empty. (The `glob` function fills them with null pointers.)

>   The `gl_offs` field is meaningful only if you use the `GLOB_DOOFFS` flag. Otherwise, the offset is always zero regardless of what is in this field, and the first real element comes at the beginning of the vector.

> `gl_closedir`
>   The address of an alternative implementation of the `closedir` function. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `void (*) (void *)`.

>   This is a GNU extension.

> `gl_readdir`
>   The address of an alternative implementation of the `readdir64` function used to read the contents of a directory. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `struct dirent64 *(*) (void *)`.

>   This is a GNU extension.

> `gl_opendir`
>   The address of an alternative implementation of the `opendir` function. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `void *(*) (const char *)`.

>   This is a GNU extension.

> `gl_stat`
>   The address of an alternative implementation of the `stat64` function to get information about an object in the filesystem. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `int (*) (const char *, struct stat64 *)`.

>   This is a GNU extension.

> `gl_lstat`
>   The address of an alternative implementation of the `lstat64` function to get information about an object in the filesystems, not following symbolic links. It is used if the `GLOB_ALTDIRFUNC` bit is set in the flag parameter. The type of this field is `int (*) (const char *, struct stat64 *)`.

>   This is a GNU extension.

> `gl_flags`
>   The flags used when `glob` was called. In addition, `GLOB_MAGCHAR` might be set. See Flags for Globbing for more details.

>   This is a GNU extension.

— Function: int glob (const char *pattern, int flags, int (*errfunc) (const char *filename, int error-code), glob_t *vector-ptr)

> The function `glob` does globbing using the pattern pattern in the current directory. It puts the result in a newly allocated vector, and stores the size and address of this vector into `*`vector-ptr. The argument flags is a combination of bit flags; see Flags for Globbing, for details of the flags.

> The result of globbing is a sequence of file names. The function `glob` allocates a string for each resulting word, then allocates a vector of type `char **` to store the addresses of these strings. The last element of the vector is a null pointer. This vector is called the word vector.

> To return this vector, `glob` stores both its address and its length (number of elements, not counting the terminating null pointer) into `*`vector-ptr.

> Normally, `glob` sorts the file names alphabetically before returning them. You can turn this off with the flag `GLOB_NOSORT` if you want to get the information as fast as possible. Usually it's a good idea to let `glob` sort them—if you process the files in alphabetical order, the users will have a feel for the rate of progress that your application is making.

> If `glob` succeeds, it returns 0. Otherwise, it returns one of these error codes:

> `GLOB_ABORTED`
>   There was an error opening a directory, and you used the flag `GLOB_ERR` or your specified errfunc returned a nonzero value. for an explanation of the `GLOB_ERR` flag and errfunc.
> `GLOB_NOMATCH`
>   The pattern didn't match any existing files. If you use the `GLOB_NOCHECK` flag, then you never get this error code, because that flag tells `glob` to pretend that the pattern matched at least one file.
> `GLOB_NOSPACE`
>   It was impossible to allocate memory to hold the result.

> In the event of an error, `glob` stores information in `*`vector-ptr about all the matches it has found so far.

> It is important to notice that the `glob` function will not fail if it encounters directories or files which cannot be handled without the LFS interfaces. The implementation of `glob` is supposed to use these functions internally. This at least is the assumptions made by the Unix standard. The GNU extension of allowing the user to provide own directory handling and `stat` functions complicates things a bit. If these callback functions are used and a large file or directory is encountered `glob` can fail.

— Function: int glob64 (const char *pattern, int flags, int (*errfunc) (const char *filename, int error-code), glob64_t *vector-ptr)

> The `glob64` function was added as part of the Large File Summit extensions but is not part of the original LFS proposal. The reason for this is simple: it is not necessary. The necessity for a `glob64` function is added by the extensions of the GNU `glob` implementation which allows the user to provide own directory handling and `stat` functions. The `readdir` and `stat` functions do depend on the choice of `_FILE_OFFSET_BITS` since the definition of the types `struct dirent` and `struct stat` will change depending on the choice.

> Beside this difference the `glob64` works just like `glob` in all aspects.

> This function is a GNU extension.