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What is Great Migrations Fortran

The Great Migrations FORTRAN to C Translator (gmFortran) is a tool that translates FORTRAN source code to correct (compilable) and clean (readable and maintainable) C source code. The C code produced can then be compiled with almost any C compiler on almost any platform to produce executable code, which in turn will produce results on the target C platform that are identical to the results produced on the source FORTRAN platform. What’s more, the C code is clean and readable so that, if you wish, you can start maintaining your application in C rather than in FORTRAN. And, unlike the original FORTRAN, the C code is portable so you can move it to multiple "open" platforms. In addition, the tool is flexible and configurable to allow extensive user control over both the input FORTRAN dialect accepted and the look of the C output generated.

This tool is intended for those who wish to convert their FORTRAN codes to C automatically; 100 percent conversion rates are achieved routinely. The conversions yield reproducible results and are repeatable and verifiable. A number of input FORTRAN dialects are supported via a dialect definition flag, and the form of the output C code is controlled by a multitude of command-line switches.

The translations are so complete and correct that the tool may also be used in conjunction with a standard C Compiler as a general-purpose, multi-dialect and portable FORTRAN compiler. It runs on multiple platforms and supports both the ANSI FORTRAN 66 and ANSI FORTRAN 77 standard dialects, as well as a large number of extensions found in various commercial FORTRAN compilers. The following FORTRAN dialects are supported: VAX, PDP, SUN, HP, CRAY, PRIME, Data General, UNISYS, and Honeywell. Some FORTRAN 90 extensions are also supported. With this product, existing FORTRAN applications will compile on "open" platforms as is, i.e., without making any changes to the original FORTRAN source code.

Validated by the GSA FORTRAN Compiler Validation Test Suite, the compiler works by translating FORTRAN source code to C source code (from where it derives its portability). It requires a C compiler/linker to produce executable code and is the ideal processor for hybrid FORTRAN/C applications. Symbolic FORTRAN debugging is supported by the symbolic debugger of the host C platform (e.g., the dbx tool for UNIX platforms).

No matter how old or how extended your FORTRAN dialect is, gmFortran will process it by first translating it to the more versatile and more portable C language. Your long-established FORTRAN programs do not have to be maintenance burdens running inefficiently on old platforms; with gmFortran, you can give them new life on contemporary platforms where you can take advantage of new technology options, including the option of program maintenance in either FORTRAN or C.


The optimized bias generates C output which is designed to compile as quickly as possible and to produce an efficient as possible executable module. This output is not very readable and is aimed at those users who wish to continue to program in FORTRAN. For these users, the C output is of no importance as such. It is merely an intermediate step and serves as input to the C compiler.

How Does It Work?

gmFortran translates FORTRAN code to C code which can then be compiled via any standard C compiler and linked with the gmFortran runtime library to produce efficient executable code. The resultant executable code produces the same results on a target platform as the original code does on the source platform.


“FORTRAN to C: Character Manipulation," Fred K. Goodman, Vol. 2, September, 1990. 

More Information


The gmFortran manual is available as PDF here.