program main
#include <petsc/finclude/petscvec.h>
  use petscvec

  implicit none

  PetscErrorCode ierr
  PetscMPIInt ::   size
  integer4     ::      fd
  PetscInt    ::   i, sz
  PetscInt, parameter   ::   m = 10
  PetscInt, parameter   ::   one = 1
  PetscInt, allocatable, dimension(:) :: t
  PetscScalar, pointer, dimension(:) :: avec
  PetscScalar, pointer, dimension(:) :: array
  Vec vec
  PetscViewer view_out, view_in
  character(len=256) :: outstring
  PetscBool :: flg

  PetscCallA(PetscInitialize(ierr))

  PetscCallMPIA(MPI_Comm_size(PETSC_COMM_WORLD, size, ierr))
  PetscCheckA(size == 1, PETSC_COMM_SELF, PETSC_ERR_WRONG_MPI_SIZE, 'This is a uniprocessor example only!')

  PetscCallA(PetscOptionsGetInt(PETSC_NULL_OPTIONS, PETSC_NULL_CHARACTER, '-m', m, flg, ierr))

  ! ----------------------------------------------------------------------
  !          PART 1: Write some data to a file in binary format
  ! ----------------------------------------------------------------------

  ! Allocate array and set values

  allocate (array(0:m - 1))
  do i = 0, m - 1
    array(i) = real(i)*10.0
  end do

  allocate (t(1))
  t(1) = m
  ! Open viewer for binary output
  PetscCallA(PetscViewerBinaryOpen(PETSC_COMM_SELF, 'input.dat', FILE_MODE_WRITE, view_out, ierr))
  PetscCallA(PetscViewerBinaryGetDescriptor(view_out, fd, ierr))

  ! Write binary output
  PetscCallA(PetscBinaryWrite(fd, t, one, PETSC_INT, ierr))
  PetscCallA(PetscBinaryWrite(fd, array, m, PETSC_SCALAR, ierr))

  ! Destroy the output viewer and work array
  PetscCallA(PetscViewerDestroy(view_out, ierr))
  deallocate (array)

  ! ----------------------------------------------------------------------
  !          PART 2: Read data from file and form a vector
  ! ----------------------------------------------------------------------

  ! Open input binary viewer
  PetscCallA(PetscViewerBinaryOpen(PETSC_COMM_SELF, 'input.dat', FILE_MODE_READ, view_in, ierr))
  PetscCallA(PetscViewerBinaryGetDescriptor(view_in, fd, ierr))

  ! Create vector and get pointer to data space
  PetscCallA(VecCreate(PETSC_COMM_SELF, vec, ierr))
  PetscCallA(VecSetSizes(vec, PETSC_DECIDE, m, ierr))

  PetscCallA(VecSetFromOptions(vec, ierr))

  PetscCallA(VecGetArray(vec, avec, ierr))

  ! Read data into vector
  PetscCallA(PetscBinaryRead(fd, t, one, PETSC_NULL_INTEGER, PETSC_INT, ierr))
  sz = t(1)

  PetscCheckA(sz >= 0, PETSC_COMM_SELF, PETSC_ERR_USER, 'Error: Must have array length > 0')

  write (outstring, '(a,i2.2,a)') 'reading data in binary from input.dat, sz =', sz, ' ...\n'
  PetscCallA(PetscPrintf(PETSC_COMM_SELF, trim(outstring), ierr))

  PetscCallA(PetscBinaryRead(fd, avec, sz, PETSC_NULL_INTEGER, PETSC_SCALAR, ierr))

  ! View vector
  PetscCallA(VecRestoreArray(vec, avec, ierr))
  PetscCallA(VecView(vec, PETSC_VIEWER_STDOUT_SELF, ierr))

  ! Free data structures
  deallocate (t)
  PetscCallA(VecDestroy(vec, ierr))
  PetscCallA(PetscViewerDestroy(view_in, ierr))
  PetscCallA(PetscFinalize(ierr))

end program

!/*TEST
!
!     test:
!        output_file: output/ex6_1.out
!
!TEST*/
