Implement open(filename, mode) and use it

src/stdlib_experimental_io.f90

@@ -1,8 +1,9 @@
 module stdlib_experimental_io
 use iso_fortran_env, only: sp=>real32, dp=>real64, qp=>real128
+use stdlib_experimental_error, only: error_stop
 implicit none
 private
-public :: loadtxt, savetxt
+public :: loadtxt, savetxt, open
 
 interface loadtxt
     module procedure sloadtxt
@@ -46,7 +47,7 @@ subroutine sloadtxt(filename, d)
 integer :: s
 integer :: nrow,ncol,i
 
-open(newunit=s, file=filename, status="old", action="read")
+s = open(filename)
 
 ! determine number of columns
 ncol = number_of_columns(s)
@@ -89,7 +90,7 @@ subroutine dloadtxt(filename, d)
 integer :: s
 integer :: nrow,ncol,i
 
-open(newunit=s, file=filename, status="old", action="read")
+s = open(filename)
 
 ! determine number of columns
 ncol = number_of_columns(s)
@@ -132,7 +133,7 @@ subroutine qloadtxt(filename, d)
 integer :: s
 integer :: nrow,ncol,i
 
-open(newunit=s, file=filename, status="old", action="read")
+s = open(filename)
 
 ! determine number of columns
 ncol = number_of_columns(s)
@@ -164,7 +165,7 @@ subroutine ssavetxt(filename, d)
 ! call savetxt("log.txt", data)
 
 integer :: s, i
-open(newunit=s, file=filename, status="replace", action="write")
+s = open(filename, "w")
 do i = 1, size(d, 1)
     write(s, *) d(i, :)
 end do
@@ -187,7 +188,7 @@ subroutine dsavetxt(filename, d)
 ! call savetxt("log.txt", data)
 
 integer :: s, i
-open(newunit=s, file=filename, status="replace", action="write")
+s = open(filename, "w")
 do i = 1, size(d, 1)
     write(s, *) d(i, :)
 end do
@@ -210,7 +211,7 @@ subroutine qsavetxt(filename, d)
 ! call savetxt("log.txt", data)
 
 integer :: s, i
-open(newunit=s, file=filename, status="replace", action="write")
+s = open(filename, "w")
 do i = 1, size(d, 1)
     write(s, *) d(i, :)
 end do
@@ -268,4 +269,39 @@ logical function whitechar(char) ! white character
 end if
 end function
 
+integer function open(filename, mode) result(u)
+! Open a file
+!
+! To open a file to read:
+!
+! u = open("somefile.txt")        # The default `mode` is "r"
+! u = open("somefile.txt", "r")
+!
+! To open a file to write:
+!
+! u = open("somefile.txt", "w")
+
+! To append to the end of the file if it exists:
+!
+! u = open("somefile.txt", "a")
+
+character(*), intent(in) :: filename
+character(*), intent(in), optional :: mode
+character(:), allocatable :: mode_
+mode_ = "r"
+if (present(mode)) mode_ = mode
+! Note: the Fortran standard says that the default values for `status` and
+! `action` are processor dependent, so we have to explicitly set them below
+if (mode_ == "r") then
+    open(newunit=u, file=filename, status="old", action="read")
+else if (mode_ == "w") then
+    open(newunit=u, file=filename, status="replace", action="write")
+else if (mode_ == "a") then
+    open(newunit=u, file=filename, position="append", status="old", &
+        action="write")
+else
+    call error_stop("Unsupported mode")
+end if
+end function
+
 end module