File Descriptors and stdio (Fortran Programming Guide)

Fortran Programming Guide

File Descriptors and `stdio`

Fortran I/O channels are in terms of unit numbers. The I/O system does not deal with unit numbers but with file descriptors. The Fortran runtime system translates from one to the other, so most Fortran programs do not have to recognize file descriptors.

Many C programs use a set of subroutines, called standard I/O (or stdio). Many functions of Fortran I/O use standard I/O, which in turn uses operating system I/O calls. Some of the characteristics of these I/O systems are listed in in the following table.

Table 11-3 Comparing I/O Between Fortran and C


	Fortran Units	Standard I/O File Pointers	File Descriptors
Files Open	Opened for reading and writing	Opened for reading; or Opened for writing; or Opened for both; or Opened for appending; See OPEN(3S)	Opened for reading; or Opened for writing; or Opened for both
Attributes	Formatted or unformatted	Always unformatted, but can be read or written with format-interpreting routines	Always unformatted
Access	Direct or sequential	Direct access if the physical file representation is direct access, but can always be read sequentially	Direct access if the physical file representation is direct access, but can always be read sequentially
Structure	Record	Byte stream	Byte stream
Form	Arbitrary nonnegative integers from 0-2147483647	Pointers to structures in the user's address space	Integers from 0-1023