9.14 ALLOCATED — Status of an allocatable entity

Description:
ALLOCATED(ARRAY) and ALLOCATED(SCALAR) check the allocation status of ARRAY and SCALAR, respectively.
Standard:
Fortran 95 and later. Note, the SCALAR= keyword and allocatable scalar entities are available in Fortran 2003 and later.
Class:
Inquiry function
Syntax:
RESULT = ALLOCATED(ARRAY)
RESULT = ALLOCATED(SCALAR)
Arguments:
ARRAY The argument shall be an ALLOCATABLE array.
SCALAR The argument shall be an ALLOCATABLE scalar.
Return value:
The return value is a scalar LOGICAL with the default logical kind type parameter. If the argument is allocated, then the result is .TRUE.; otherwise, it returns .FALSE.
Example:
program test_allocated
  integer :: i = 4
  real(4), allocatable :: x(:)
  if (.not. allocated(x)) allocate(x(i))
end program test_allocated

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Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gfortran/ALLOCATED.html