Over the years, the Fortran standards committee has striven to keep each new standard backward-compatible with previous releases. Fortran is one of the oldest high-level languages; much old code is still in use. The committee has admirably succeeded, and programmers have known that they could continue to write programs that contained old features and that they could add features of the new standards whenever it was convenient, useful, or appropriate. Each new standard has marked only a few old features as “obsolescent,” defined as “A feature that is considered redundant but that is still in frequent use.” Those so marked in one standard may be “deleted” in a subsequent one. The standard describes a “deleted” feature as “A feature in a previous Fortran standard that is considered to have been redundant and largely unused.” This chapter describes many of these old features and the new ones provided by the modern Fortran standards (meaning from Fortran 90 and on) that you can use to replace them. We note the status of the each old feature. For further details, see the appropriate language standard: Fortran 90, Reference [40]; Fortran 95: Reference [42]; Fortran 2003, Reference [39]; and Fortran 2008, Reference [43].

Statements

Replace common blocks with modules.

In FORTRAN 66 and FORTRAN 77, programmers stored global data in common blocks. A program could have one unnamed common block and any number of named blocks.