Add is_windows and test it

src/stdlib_io_filesystem.F90

@@ -6,13 +6,34 @@ module stdlib_io_filesystem
     implicit none
     private
 
-    public :: exists, list_dir, run, temp_dir
+    public :: temp_dir, is_windows, exists, list_dir, run
 
     character(*), parameter :: temp_dir = 'temp'
     character(*), parameter :: listed_contents = temp_dir//'/listed_contents.txt'
 
 contains
 
+    !> Version: experimental
+    !>
+    !> Whether the operating system is Windows.
+    !> [Specification](../page/specs/stdlib_io.html#is_windows)
+    logical function is_windows()
+        character(len=255) :: value
+        integer :: length, stat
+
+        call get_environment_variable('OSTYPE', value, length, stat)
+        if (stat == 0 .and. length > 0 .and. (index(value, 'win') > 0 .or. index(value, 'msys') > 0)) then
+            is_windows = .true.; return
+        end if
+
+        call get_environment_variable('OS', value, length, stat)
+        if (stat == 0 .and. length > 0 .and. index(value, 'Windows_NT') > 0) then
+            is_windows = .true.; return
+        end if
+
+        is_windows = .false.
+    end
+
     !> Version: experimental
     !>
     !> Whether a file or directory exists at the given path.

test/io/test_filesystem.f90

@@ -17,6 +17,7 @@ subroutine collect_filesystem(testsuite)
         type(unittest_type), allocatable, intent(out) :: testsuite(:)
 
         testsuite = [ &
+            new_unittest("fs_file_is_windows", fs_is_windows), &
             new_unittest("fs_file_not_exists", fs_file_not_exists, should_fail=.true.), &
             new_unittest("fs_file_exists", fs_file_exists), &
             new_unittest("fs_current_dir_exists", fs_current_dir_exists), &
@@ -30,6 +31,20 @@ subroutine collect_filesystem(testsuite)
             ]
     end
 
+    subroutine fs_is_windows(error)
+        type(error_type), allocatable, intent(out) :: error
+
+        character(len=255) :: value
+        integer :: length, stat
+
+        call get_environment_variable('HOMEDRIVE', value, length, stat)
+        if (is_windows()) then
+            call check(error, stat == 0 .and. length > 0, "Windows should be detected.")
+        else
+            call check(error, stat /= 0 .and. length == 0, "Windows should not be detected.")
+        end if
+    end
+
     subroutine fs_file_not_exists(error)
         type(error_type), allocatable, intent(out) :: error