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.Dd $Mdocdate: April 15 2024 $
.Dt SCANDIR 3
.Os
.Sh NAME
.Nm scandir ,
.Nm scandirat ,
.Nm alphasort
.Nd scan a directory
.Sh SYNOPSIS
.In sys/types.h
.In dirent.h
.Ft int
.Fo scandir
.Fa "const char *dirname"
.Fa "struct dirent ***namelist"
.Fa "int (*select)(const struct dirent *)"
.Fa "int (*compar)(const struct dirent **, const struct dirent **)"
.Fc
.Ft int
.Fo scandirat
.Fa "int dirfd"
.Fa "const char *dirname"
.Fa "struct dirent ***namelist"
.Fa "int (*select)(const struct dirent *)"
.Fa "int (*compar)(const struct dirent **, const struct dirent **)"
.Fc
.Ft int
.Fn alphasort "const struct dirent **d1" "const struct dirent **d2"
.Sh DESCRIPTION
The
.Fn scandir
function reads the directory
.Fa dirname
and builds an array of pointers to directory
entries using
.Xr malloc 3 .
It returns the number of entries in the array.
A pointer to the array of directory entries is stored in the location
referenced by
.Fa namelist .
.Pp
The
.Fa select
parameter is a pointer to a user-supplied subroutine which is called by
.Fn scandir
to select which entries are to be included in the array.
The select routine is passed a
pointer to a directory entry and should return a non-zero
value if the directory entry is to be included in the array.
If
.Fa select
is
.Dv NULL ,
then all directory entries will be included.
.Pp
The
.Fa compar
parameter is a pointer to a user-supplied subroutine which is passed to
.Xr qsort 3
to sort the completed array.
If this pointer is
.Dv NULL ,
the array is not sorted.
.Pp
The
.Fn alphasort
function is a routine which can be used for the
.Fa compar
parameter to sort the array alphabetically.
.Pp
The memory allocated for the array can be deallocated with
.Xr free 3 ,
by freeing each pointer in the array and then the array itself.
.Pp
The
.Fn scandirat
function is similar to
.Fn scandir ,
but takes an additional
.Fa dirfd
argument.
If
.Fa dirname
is relative,
.Fa dirfd
must be a valid file descriptor referencing a directory, in which case the
.Fa dirname
lookup is performed relative to the directory referenced by
.Fa dirfd .
If
.Fa dirfd
has the special value
.Va AT_FDCWD ,
then the current process directory is used as the base for relative lookups.
See
.Xr openat 2
for additional details.
.Sh DIAGNOSTICS
Returns \-1 if the directory cannot be opened for reading or if
.Xr malloc 3
cannot allocate enough memory to hold all the data structures.
.Sh SEE ALSO
.Xr malloc 3 ,
.Xr opendir 3 ,
.Xr qsort 3 ,
.Xr dir 5
.Sh STANDARDS
The
.Fn scandir
and
.Fn alphasort
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn scandir
and
.Fn alphasort
functions appeared in
.Bx 4.2 .
.Pp
The argument types for
.Fn alphasort
and for the
.Fa compar
argument to
.Fn scandir
were originally
.Vt "void *" ,
then changed to
.Vt "const void *" ,
and then finally changed by
.St -p1003.1-2008
to their current form of
.Vt "const struct dirent **" .
Similarly, the
.Fn select
argument to
.Fn scandir
was originally
.Vt "struct dirent *"
until it was changed to its current form of
.Vt "const struct dirent *" .