File Permissions

C programs typically open input files for reading and output files for writing or for reading and writing. A f77 program can OPEN a file READONLY or with READWRITE='READ' or 'WRITE' or 'READWRITE'. f90 supports the READWRITE specifier, but not READONLY.

Fortran tries to open a file with the maximum permissions possible, first for both reading and writing, then for each separately.

This event occurs transparently and is of concern only if you try to perform a READ, WRITE, or ENDFILE operation but you do not have permission. Magnetic tape operations are an exception to this general freedom, since you can have write permissions on a file, but not have a write ring on the tape.