Fortran Wiki
iso_fortran_env

iso_fortran_env is an intrinsic module that provides the following constants relating to the Fortran environment:

character_storage_size

the size, in bits, of the character storage unit.

error_unit

the unit number used for error reporting (stderr).

file_storage_size

the size, in bits, of the file storage unit.

input_unit

the unit number used for input (stdin).

iostat_end

the value that is assigned to the iostat= specifier if an end-of-file condition occurs during a read statement.

iostat_eor

the value that is assigned to the iostat= specifier if an end-of-record condition occurs during a read statement.

numeric_storage_size

the size, in bits, of the numeric storage unit.

output_unit

the unit number used for output (stdout).