Write Derived Type Formatted to Disk

[MWind2]

How does one format a derived type to be saved with formatting, and later be read back into instance(ignore round trip variable equality for reals)?  Sample with bad format attempt:

program ftype

    implicit none

    ! Variables
    integer ios10
    type t0
        character(len=32)   :: name = '.'
        real, dimension(56) :: awclose = -1.0
        integer             :: id = -1
        LOGICAL             :: IS_IT_INITIALIZED = .FALSE.
    end type t0
   type(t0), dimension(4)         :: at0
    ! Body of ftype
    
    open (10,file='testat0.dat',form='FORMATTED',access='sequential',IOSTAT=ios10)
    write (10,10) at0(1)
    !
    !10   FORMAT (t0%name, t0%awclose 5F15.8, t0%id)
    close (10)
    end program ftype

[Steve_Lionel]

Fortran 2018 has a treat for you - EX format. This writes (and reads) reals in a hexadecimal notation that reproduces the bit pattern exactly.  It's supported in the Intel 2021 beta (and will be when it becomes a product.)

Here's a modified version of your example that demonstrates the feature (I am not sure what you intended with that commented-out FORMAT that isn't a format.)

program ftype

    implicit none

    ! Variables
    integer ios10
    type t0
        character(len=32)   :: name = '.'
        real, dimension(5) :: awclose = -1.0
        integer             :: id = -1
        LOGICAL             :: IS_IT_INITIALIZED = .FALSE.
    end type t0
   type(t0), dimension(4)         :: at0
    ! Body of ftype
    
    call random_number(at0(1)%awclose)
    print *, at0(1)%awclose
    open (10,file='testat0.dat',form='FORMATTED',access='sequential',IOSTAT=ios10)
    write (10,10) at0(1)
    10 format (A,1X,5EX16.6E2,1X,I5,1X,L1)
    rewind (10)
    read (10,10) at0(2)
    print *, at0(2)%awclose
    !
    !10   FORMAT (t0%name, t0%awclose 5F15.8, t0%id)
    close (10)
    end program ftype

D:\Projects>ifort t.f90
Intel(R) Visual Fortran Intel(R) 64 Compiler for applications running on Intel(R) 64, Version 2021.1 Beta Build 20200602
Copyright (C) 1985-2020 Intel Corporation.  All rights reserved.

Microsoft (R) Incremental Linker Version 14.27.29111.0
Copyright (C) Microsoft Corporation.  All rights reserved.

-out:t.exe
-subsystem:console
t.obj

D:\Projects>t.exe
  3.9208680E-07  2.5480442E-02  0.3525161      0.6669145      0.9630555
  3.9208680E-07  2.5480442E-02  0.3525161      0.6669145      0.9630555

D:\Projects>type testat0.dat
.                                  0XD.280000P-25  0XD.0BC5C0P-09  0XB.47CFF0P-05  0XA.ABAE80P-04  0XF.68ACE0P-04    -1 F

[MWind2]

The following seems to do most of what was desired:

program ftype

    implicit none

    ! Variables
    integer i
    integer ios10
    type t0
        character(len=32)   :: name = '.0123456789'
        real, dimension(56) :: awclose = -1.0
        integer             :: id = -1
        LOGICAL             :: IS_IT_INITIALIZED = .FALSE.
    end type t0
   type(t0), dimension(4)         :: at0
    ! Body of ftype
    do i=1, 56
        at0(1)%awclose(i) = at0(1)%awclose(i)+i*1.0
    end do
    open (10,file='testat0.trgx',form='FORMATTED',access='sequential',IOSTAT=ios10)
    write (10,10) at0(1)
!10  FORMAT (A32,5F15.6, 5F15.6, 5F15.6, 5F15.6, 5F15.6, 5F15.6, 5F15.6,5F15.6,5F15.6,5F15.6,6F15.6,I8,L2)
    10   FORMAT (A32,56F15.6, I8,L2)
    close (10)
    end program ftype

It would seem that formatting 5 floats and then a crlf would defeat the delimiters of a record so to display would need more code and the result not be readable as a t0 record

[andrew_4619]

Steve clearly changed the example to 5 just to make it more compact to display the output. Note that he changed the derived type component to 5 elements also. It seem you have a working solution know.

[Steve_Lionel]

Generally if you format reals to three more significant digits than the datatype holds, you won't lose any bits. For single precision, I'd suggest 10 digits.