Fortran

Infobox programming language
name = Fortran

caption = "The Fortran Automatic Coding System for the IBM 704" (October 15, 1956), the first Programmer's Reference Manual for Fortran
paradigm = multi-paradigm: procedural, imperative, structured, object-oriented
year = 1957
designer = John Backus
developer = John Backus & IBM
latest release version = Fortran 2003
latest release date = 2003
typing = strong, static
implementations = Absoft, GFortran, G95, Intel, Lahey/Fujitsu, Open Watcom, Pathscale, PGI, Silverfrost, Sun, XL Fortran, others
dialects =
influenced_by =
influenced = ALGOL 58, PL/I
operating_system =
license =
website =

Fortran (previously FORTRAN [The names of earlier versions of the language through FORTRAN 77 were conventionally spelled in all-caps (FORTRAN 77 was the version in which the use of lowercase letters in keywords was strictly nonstandard). The capitalization has been dropped in referring to newer versions beginning with Fortran 90. The official language standards now refer to the language as "Fortran." Because the capitalization (or lack thereof) of the word "FORTRAN" was never 100% consistent in actual usage, and because many hold impassioned beliefs on the issue, this article, rather than attempt to be normative, adopts the convention of using the all-caps "FORTRAN" in referring to versions of FORTRAN through FORTRAN 77 and the title-caps "Fortran" in referring to versions of Fortran from Fortran 90 onward. This convention is reflected in the capitalization of "FORTRAN" in the ANSI X3.9-1966 (FORTRAN 66) and ANSI X3.9-1978 (FORTRAN 77) standards and the title caps "Fortran" in the ANSI X3.198-1992 (Fortran 90) standard.] ) is a general-purpose, [Since FORTRAN 77, which introduced the CHARACTER data type.] procedural, [Since FORTRAN II (1958).] imperative programming language that is especially suited to numeric computation and scientific computing. Originally developed by IBM in the 1950s for scientific and engineering applications, Fortran came to dominate this area of programming early on and has been in continual use for over half a century in computationally intensive areas such as numerical weather prediction, finite element analysis, computational fluid dynamics (CFD), computational physics, and computational chemistry. It is one of the most popular languages in the area of High-performance computing and programs to benchmark and rank the world's fastest supercomputers are written in Fortran [http://en.wikipedia.org/wiki/LINPACK and http://www.top500.org/project/linpack] .

Fortran (a blend word derived from "The IBM Mathematical Formula Translating System") encompasses a lineage of versions, each of which evolved to add extensions to the language while usually retaining compatibility with previous versions. Successive versions have added support for processing of character-based data (FORTRAN 77), array programming, module-based programming and object-based programming (Fortran 90 / 95), and object-oriented and generic programming (Fortran 2003).

History

[
right|thumb|320px|An_IBM 704 mainframe (image courtesy of LLNL)] In late 1953, John W. Backus submitted a proposal to his superiors at IBM to develop a more efficient alternative to assembly language for programming their IBM 704 mainframe computer. Backus' historic FORTRAN team consisted of programmers Richard Goldberg, Sheldon F. Best, Harlan Herrick, Peter Sheridan, Roy Nutt, Robert Nelson, Irving Ziller, Lois Haibt and David Sayre. [http://www.softwarepreservation.org/projects/FORTRAN/index.html#By_FORTRAN_project_members]

A draft specification for "The IBM Mathematical Formula Translating System" was completed by mid-1954. The first manual for FORTRAN appeared in October 1956, with the first FORTRAN compiler delivered in April 1957. This was an optimizing compiler, because customers were reluctant to use a high-level programming language unless its compiler could generate code whose performance was comparable to that of hand-coded assembly language.

While the community was skeptical that this new method could possibly out-perform hand-coding, it reduced the amount of programming statements necessary to operate a machine by a factor of 20, and quickly gained acceptance. Said creator John Backus during a 1979 interview with Think, the IBM employee magazine, "Much of my work has come from being lazy. I didn't like writing programs, and so, when I was working on the IBM 701 (an early computer), writing programs for computing missile trajectories, I started work on a programming system to make it easier to write programs." [ [http://www.msnbc.msn.com/id/17704662/ Fortran creator John Backus dies - Gadgets - MSNBC.com ] ]

The language was widely adopted by scientists for writing numerically intensive programs, which encouraged compiler writers to produce compilers that could generate faster and more efficient code. The inclusion of a complex number data type in the language made Fortran especially suited to technical applications such as electrical engineering.

By 1960, versions of FORTRAN were available for the IBM 709, 650, 1620, and 7090 computers. Significantly, the increasing popularity of FORTRAN spurred competing computer manufacturers to provide FORTRAN compilers for their machines, so that by 1963 over 40 FORTRAN compilers existed. For these reasons, FORTRAN is considered to be the first widely used programming language supported across a variety of computer architectures.

The development of FORTRAN paralleled the early evolution of compiler technology; indeed many advances in the theory and design of compilers were specifically motivated by the need to generate efficient code for FORTRAN programs.

FORTRAN

The initial release of FORTRAN for the IBM 704 contained 32 statements, including:

* DIMENSION and EQUIVALENCE statements
* Assignment statements
* Three-way "arithmetic" IF statement. [Note: It is commonly believed that this statement corresponded to a three-way branch instruction on the IBM 704. This is not true, the 704 branch instructions all contained only one destination address (e.g., TZE — Transfer AC Zero, TNZ — Transfer AC Not Zero, TPL — Transfer AC Plus, TMI — Transfer AC Minus). The machine (and its successors in the 700/7000 series) did have a three-way "skip" instruction (CAS — Compare AC with Storage), which was probably the origin of this belief, but using this instruction to implement the IF would consume 4 instruction words, require the constant Zero in a word of storage, and take 3 machine cycles to execute; using the Transfer instructions to implement the IF could be done in 1 to 3 instruction words, required no constants in storage, and take 1 to 3 machine cycles to execute. An optimizing compiler like FORTRAN would most likely select the more compact and usually faster Transfers instead of the Compare (use of Transfers also allowed the FREQUENCY statement to optimize IFs, which could not be done using the Compare). Also the Compare considered -0 and +0 to be different values while the Transfer Zero and Transfer Not Zero considered them to be the same.]
* IF statements for checking exceptions (ACCUMULATOR OVERFLOW, QUOTIENT OVERFLOW, and DIVIDE CHECK); and IF statements for manipulating sense switches and sense lights
* GOTO, computed GOTO, ASSIGN, and assigned GOTO
* DO loops
* Formatted I/O: FORMAT, READ, READ INPUT TAPE, WRITE, WRITE OUTPUT TAPE, PRINT, and PUNCH
* Unformatted I/O: READ TAPE, READ DRUM, WRITE TAPE, and WRITE DRUM
* Other I/O: END FILE, REWIND, and BACKSPACE
* PAUSE, STOP, and CONTINUE
* FREQUENCY statement (for providing optimization hints to the compiler) [The FREQUENCY statement in FORTRAN was used originally and optionally to give branch probabilities for the three branch cases of the Arithmetic IF statement to bias the way code was generated and order of the basic blocks of code generated, in the global optimisation sense, were arranged in memory for optimality. The first FORTRAN compiler used this weighting to do a Monte Carlo simulation of the run-time generated code at compile time. It was very sophisticated for its time. This technique is documented in the original article in 1957 on the first FORTRAN compiler implementation by J. Backus, et al. Many years later, the FREQUENCY statement had no effect on the code, and was treated as a comment statement, since the compilers no longer did this kind of compile-time simulation.

Below is a part of the 1957 paper, "The FORTRAN Automatic Coding System" by Backus, et al., with this snippet on the FREQUENCY statement and its use in a compile-time Monte Carlo simulation of the run-time to optimise the code generated. Quoting …

The fundamental unit of program is the basic block; a basic block is a stretch of program which has a single entry point and a single exit point. The purpose of section 4 is to prepare for section 5 a table of predecessors (PRED table) which enumerates the basic blocks and lists for every basic block each of the basic blocks which can be its immediate predecessor in flow, together with the absolute frequency of each such basic block link. This table is obtained by an actual "execution" of the program in Monte-Carlo fashion, in which the outcome of conditional transfers arising out of IF-type statements and computed GO TO'S is determined by a random number generator suitably weighted according to whatever FREQUENCY statements have been provided.

]

FORTRAN II

IBM's "FORTRAN II" appeared in 1958. The main enhancement was to support procedural programming by allowing user-written subroutines and functions. Six new statements were introduced:

* SUBROUTINE, FUNCTION, and END
* CALL and RETURN
* COMMON

Over the next few years, FORTRAN II would also add support for the DOUBLE PRECISION and COMPLEX data types.

imple Fortran II program

This program, for Heron's formula, has one data card input, with simple zero-data edit check. If one of the input values is zero or negative, then the program will end with an error code of "STOP 1" in the job control card listing following the execution of the program. Normal output will be one line printed with A, B, C, and AREA on the "report" page following the compilation with no specific units are stated; and with a normal "STOP" in the job card listing.

C AREA OF A TRIANGLE WITH A STANDARD SQUARE ROOT FUNCTION C INPUT - CARD READER UNIT 5, INTEGER INPUTC OUTPUT - LINE PRINTER UNIT 6, REAL OUTPUTC INPUT ERROR DISPLAY ERROR OUTPUT CODE 1 IN JOB CONTROL LISTING READ INPUT TAPE 5, 501, IA, IB, IC 501 FORMAT (3I5)C IA, IB, AND IC MAY NOT BE NEGATIVEC FURTHERMORE, THE SUM OF TWO SIDES OF A TRIANGLEC IS GREATER THAN THE THIRD SIDE, SO WE CHECK FOR THAT, TOO IF (IA) 777, 777, 701 701 IF (IB) 777, 777, 702 702 IF (IC) 777, 777, 703 703 IF (IA+IB-IC) 777,777,704 704 IF (IA+IC-IB) 777,777,705 705 IF (IB+IC-IA) 777,777,799 777 STOP 1C USING HERON'S FORMULA WE CALCULATE THEC AREA OF THE TRIANGLE 799 S = FLOATF (IA + IB + IC) / 2.0 AREA = SQRT( S * (S - FLOATF(IA)) * (S - FLOATF(IB)) * + (S - FLOATF(IC))) WRITE OUTPUT TAPE 6, 601, IA, IB, IC, AREA 601 FORMAT (4H A= ,I5,5H B= ,I5,5H C= ,I5,8H AREA= ,F10.2, + 13H SQUARE UNITS) STOP END

FORTRAN III

IBM also developed a "FORTRAN III" in 1958 that allowed for inline assembler code among other features; however, this version was never released as a product. Like the 704 FORTRAN and FORTRAN II, FORTRAN III included machine-dependent features that made code written in it unportable from machine to machine. Early versions of FORTRAN provided by other vendors suffered from the same disadvantage.

FORTRAN IV

Starting in 1961, as a result of customer demands, IBM began development of a "FORTRAN IV" that removed the machine-dependent features of FORTRAN II (such as READ INPUT TAPE), while adding new features such as a LOGICAL data type, logical Boolean expressions and the "logical IF statement" as an alternative to the "arithmetic IF statement." FORTRAN IV was eventually released in 1962, first for the IBM 7030 ("Stretch") computer, followed by versions for the IBM 7090 and IBM 7094.

By 1965, Fortran IV was supposed to be the "standard" and in compliance with American Standards Association X3.4.3 FORTRAN Working Group.cite book|author=McCracken, Daniel D.|title=A Guide to FORTRAN IV Programming|publisher=John Wiley & Sons, Inc., New York|year=1965(3rd printing 1968)|id=LCCCN 65-26848 Preface p. "v" ]

FORTRAN 66

Perhaps the most significant development in the early history of FORTRAN was the decision by the "American Standards Association" (now ANSI) to form a committee to develop an "American Standard Fortran." The resulting two standards, approved in March 1966, defined two languages, "FORTRAN" (based on FORTRAN IV, which had served as a "de facto" standard), and "Basic FORTRAN" (based on FORTRAN II, but stripped of its machine-dependent features). The FORTRAN defined by the first standard became known as "FORTRAN 66" (although many continued to refer to it as FORTRAN IV, the language upon which the standard was largely based). FORTRAN 66 effectively became the first "industry-standard" version of FORTRAN. FORTRAN 66 included:

* Main program, SUBROUTINE, FUNCTION, and BLOCK DATA program units
* INTEGER, REAL, DOUBLE PRECISION, COMPLEX, and LOGICAL data types
* COMMON, DIMENSION, and EQUIVALENCE statements
* DATA statement for specifying initial values
* Intrinsic and EXTERNAL ("e.g.," library) functions
* Assignment statement
* GOTO, assigned GOTO, and computed GOTO statements
* Logical IF and arithmetic (three-way) IF statements
* DO loops
* READ, WRITE, BACKSPACE, REWIND, and ENDFILE statements for sequential I/O
* FORMAT statement
* CALL, RETURN, PAUSE, and STOP statements
* Hollerith constants in DATA and FORMAT statements, and as actual arguments to procedures
* Identifiers of up to six characters in length
* Comment lines

FORTRAN 77

After the release of the FORTRAN 66 standard, compiler vendors introduced a number of extensions to "Standard Fortran", prompting ANSI in 1969 to begin work on revising the 1966 standard. Final drafts of this revised standard circulated in 1977, leading to formal approval of the new FORTRAN standard in April 1978. The new standard, known as "FORTRAN 77", added a number of significant features to address many of the shortcomings of FORTRAN 66:

* Block IF and END IF statements, with optional ELSE and ELSE IF clauses, to provide improved language support for structured programming
* DO loop extensions, including parameter expressions, negative increments, and zero trip counts
* OPEN, CLOSE, and INQUIRE statements for improved I/O capability
* Direct-access file I/O
* IMPLICIT statement
* CHARACTER data type, with vastly expanded facilities for character input and output and processing of character-based data
* PARAMETER statement for specifying constants
* SAVE statement for persistent local variables
* Generic names for intrinsic functions
* A set of intrinsics (LGE, LGT, LLE, LLT) for lexical comparison of strings, based upon the ASCII collating sequence.: "(ASCII functions were demanded by the U. S. Department of Defense, in their conditional approval vote.) "

In this revision of the standard, a number of features were removed or altered in a manner that might invalidate previously standard-conforming programs."(Removal was the only allowable alternative to X3J3 at that time, since the concept of "deprecation" was not yet available for ANSI standards.)"While most of the 24 items in the conflict list (see Appendix A2 of X3.9-1978) addressed loopholes or pathological cases permitted by the previous standard but rarely used, a small number of specific capabilities were deliberately removed, such as:
* Hollerith constants and Hollerith data, such as::: GREET = 12HHELLO THERE!
* Reading into a H edit (Hollerith field) descriptor in a FORMAT specification.
* Overindexing of array bounds by subscripts.:: DIMENSION A(10,5):: Y= A(11,1)
* Transfer of control into the range of a DO loop (also known as "Extended Range").

An important practical extension to FORTRAN 77 was the release of MIL-STD-1753 in 1978. This specification, developed by the U. S. Department of Defense, standardized a number of features implemented by most FORTRAN 77 compilers but not included in the ANSI FORTRAN 77 standard. These features would eventually be incorporated into the Fortran 90 standard.

* DO WHILE and END DO statements
* INCLUDE statement
* IMPLICIT NONE variant of the IMPLICIT statement
* Bit manipulation intrinsic functions, based on similar functions included in Industrial Real-Time Fortran (ANSI/ISA S61.1 (1976))

The IEEE 1003.9 POSIX Standard, released in 1991, provided a simple means for Fortran-77 programmers to issue POSIX system calls. Over 100 calls were defined in the document — allowing access to POSIX-compatible process control, signal handling, file system control, device control, procedure pointing, and stream I/O in a portable manner.

The development of a revised standard to succeed FORTRAN 77 would be repeatedly delayed as the standardization process struggled to keep up with rapid changes in computing and programming practice. In the meantime, as the "Standard FORTRAN" for nearly fifteen years, FORTRAN 77 would become the historically most important dialect.

Control Data Corporation computers had another version of FORTRAN 77, called Minnesota FORTRAN, with variations in output constructs, special uses of COMMONs and DATA statements, optimizations code levels for compiling, and detailed error listings, extensive warning messages, and debugs. [ [http://www.chilton-computing.org.uk/acd/literature/reports/p008.htm Chilton Computing with FORTRAN] ]

Fortran 90

The much delayed successor to FORTRAN 77, informally known as "Fortran 90", was finally released as an ISO standard in 1991 and an ANSI Standard in 1992. This major revision added many new features to reflect the significant changes in programming practice that had evolved since the 1978 standard:

* Free-form source input, also with lowercase Fortran keywords
* Identifiers up to 31 characters in length
* Inline comments
* Ability to operate on arrays (or array sections) as a whole, thus greatly simplifying math and engineering computations.
** whole, partial and masked array assignment statements and array expressions, such as X(1:N)=R(1:N)*COS(A(1:N)))
** WHERE statement for selective array assignment
** array-valued constants and expressions,
** user-defined array-valued functions and array constructors.
* RECURSIVE procedures
* Modules, to group related procedures and data together, and make them available to other program units, including the capability to limit the accessibility to only specific parts of the module.
* A vastly improved argument-passing mechanism, allowing interfaces to be checked at compile time
* User-written interfaces for generic procedures
* Operator overloading
* Derived/abstract data types
* New data type declaration syntax, to specify the data type and other attributes of variables
* Dynamic memory allocation by means of the ALLOCATABLE attribute and the ALLOCATE and DEALLOCATE statements
* POINTER attribute, pointer assignment, and NULLIFY statement to facilitate the creation and manipulation of dynamic data structures
* Structured looping constructs, with an END DO statement for loop termination, and EXIT and CYCLE statements for "breaking out" of normal DO loop iterations in an orderly way
* SELECT . . . CASE construct for multi-way selection
* Portable specification of numerical precision under the user's control
* New and enhanced intrinsic procedures.

Obsolescence & deletions

Unlike the previous revision, Fortran 90 did not delete any features."(Appendix B.1 says, "The list of deleted features in this standard is empty.")"Any standard-conforming FORTRAN 77 program is also standard-conforming under Fortran 90, and either standard should be usable to define its behavior.

A small set of features were identified as "obsolescent"and expected to be removed in a future standard.

Fortran 95

"Fortran 95" was a minor revision, mostly to resolve some outstanding issues from the Fortran 90 standard. Nevertheless, Fortran 95 also added a number of extensions, notably from the High Performance Fortran specification:

* FORALL and nested WHERE constructs to aid vectorization
* User-defined PURE and ELEMENTAL procedures
* Pointer initialization and structure default initialization.

A number of intrinsic functions were extended (for example a dim argument was added to the maxloc intrinsic).

Several features noted in Fortran 90 to be deprecated were removed from Fortran 95:

* REAL and DOUBLE PRECISION DO variables
* Branching to an END IF statement from outside its block
* PAUSE statement
* ASSIGN and assigned GOTO statement, and assigned format specifiers
* H edit descriptor.

An important supplement to Fortran 95 was the ISO technical report "TR-15581: Enhanced Data Type Facilities", informally known as the "Allocatable TR." This specification defined enhanced use of ALLOCATABLE arrays, prior to the availability of fully Fortran 2003-compliant Fortran compilers. Such uses include ALLOCATABLE arrays as derived type components, in procedure dummy argument lists, and as function return values. (ALLOCATABLE arrays are preferable to POINTER-based arrays because ALLOCATABLE arrays are guaranteed by Fortran 95 to be deallocated automatically when they go out of scope, eliminating the possibility of memory leakage. In addition, aliasing is not an issue for optimization of array references, allowing compilers to generate faster code than in the case of pointers.)

Another important supplement to Fortran 95 was the ISO technical report "TR-15580: Floating-point exception handling", informally known as the "IEEE TR." This specification defined support for IEEE floating-point arithmetic and floating point exception handling.

Conditional compilation and varying length strings

In addition to the mandatory "Base language"(defined in ISO/IEC 1539-1 : 1997),the Fortran 95 language also includes two optional modules:
* Varying character strings (ISO/IEC 1539-2 : 2000)
* Conditional compilation (ISO/IEC 1539-3 : 1998) which, together, comprise the multi-part International Standard (ISO/IEC 1539).

According to the standards developers,"the optional parts describe self-contained features which have been requested by a substantial body of users and/or implementors, but which are not deemed to be of sufficient generality for them to be required in all standard-conforming Fortran compilers." Nevertheless, if a standard-conforming Fortran does provide such options, then they "must be provided in accordance with the description of those facilities in the appropriate Part of the Standard."

Fortran 2003

The most recent standard, "Fortran 2003", is a major revision introducing many new features. A comprehensive summary of the new features of Fortran 2003 is available at the Fortran Working Group (WG5) official Web site. [ [http://www.nag.co.uk/sc22wg5/ Fortran Working Group (WG5)] . It may also be downloaded as a [ftp://ftp.nag.co.uk/sc22wg5/N1551-N1600/N1579.pdf PDF file] or [ftp://ftp.nag.co.uk/sc22wg5/N1551-N1600/N1579.ps.gz gzipped PostScript file] .]

From that article, the major enhancements for this revision include:
* Derived type enhancements: parameterized derived types, improved control of accessibility, improved structure constructors, and finalizers.
* Object oriented programming support: type extension and inheritance, polymorphism, dynamic type allocation, and type-bound procedures.
* Data manipulation enhancements: allocatable components (incorporating TR 15581), deferred type parameters, VOLATILE attribute, explicit type specification in array constructors and allocate statements, pointer enhancements, extended initialization expressions, and enhanced intrinsic procedures.
* Input/output enhancements: asynchronous transfer, stream access, user specified transfer operations for derived types, user specified control of rounding during format conversions, named constants for preconnected units, the FLUSH statement, regularization of keywords, and access to error messages.
* Procedure pointers.
* Support for IEEE floating-point arithmetic and floating point exception handling (incorporating TR 15580).
* Interoperability with the C programming language.
* Support for international usage: access to ISO 10646 4-byte characters and choice of decimal or comma in numeric formatted input/output.
* Enhanced integration with the host operating system: access to command line arguments, environment variables, and processor error messages.

An important supplement to Fortran 2003 was the ISO technical report "TR-19767: Enhanced module facilities in Fortran." This report provided "submodules," which make Fortran modules more similar to Modula-2 modules. They are similar to Ada private child subunits. This allows the specification and implementation of a module to be expressed in separate program units, which improves packaging of large libraries, allows preservation of trade secrets while publishing definitive interfaces, and prevents compilation cascades.

Fortran 2008

Efforts are underway to develop a revision to Fortran 2003, tentatively called Fortran 2008. As with Fortran 95, this is intended to be a minor upgrade, incorporating clarifications and corrections to Fortran 2003, as well as introducing a select few new capabilities. As of February 2007, the proposed new capabilities include [A full list is in the report available at PDFlink|http://www.fortran.bcs.org/2006/ukfortran06.pdf|24.2 KiB .]
* Co-array Fortran – a parallel processing model
* BIT data type

In August 2007, the BIT data type was removed. In February 2008, Coarrays were scaled back: Parallel I/O and teams were removed.

The complete original work plan is available at http://j3-fortran.org/doc/year/07/07-010.html.

The legacy of FORTRAN

Since Fortran has been in use for more than fifty years, there is a vast body of Fortran in daily use throughout the scientific and engineering communities. It is the primary language for some of the most intensive supercomputing tasks, such as weather and climate modeling, computational fluid dynamics, computational chemistry, computational economics, and computational physics. Even today, half a century later, many of the floating-point benchmarks to gauge the performance of new computer processors are still written in Fortran ("e.g.," [http://www.spec.org/cpu2006/CFP2006/ CFP2006] , the floating-point component of the SPEC [http://www.spec.org/cpu2006/ CPU2006] benchmarks).

Language features

The "Fortran language features" described are intended to be a fairly comprehensive overview of the Fortran language; full details may be found in any of several Fortran textbooks. Only those features widely used in new programs are described, as few of the historic features are used in modern programs. Still, most have been retained in the language to maintain backward compatibility.

Portability

Portability was a problem in the early days because there was no agreed standard—not even IBM's reference manual—and computer companies vied to differentiate their offerings from others by providing incompatible features. Standards have improved portability. The 1966 standard provided a reference syntax and semantics, but vendors continued to provide incompatible extensions. Although careful programmers were coming to realize that use of incompatible extensions caused expensive portability problems, and were therefore using programs such as "The PFORT Verifier," it was not until after the 1977 standard, when the National Bureau of Standards (now NIST) published "FIPS PUB 69", that processors purchased by the U.S. Government were required to diagnose extensions of the standard. Rather than offer two processors, essentially every compiler eventually had at least an option to diagnose extensions.

Incompatible extensions were not the only portability problem. For numerical calculations, it is important to take account of the characteristics of the arithmetic. This was addressed by Fox et al. in the context of the 1966 standard by the "PORT" library. The ideas therein became widely used, and were eventually incorporated into the 1990 standard by way of intrinsic inquiry functions. The widespread (now almost universal) adoption of the IEEE 754 standard for binary floating-point arithmetic has essentially removed this problem.

Access to the computing environment (e.g. the program's command line, environment variables, textual explanation of error conditions) remained a problem until it was addressed by the 2003 standard.

Large collections of "library" software that could be described as being loosely-related to engineering and scientific calculations, such as graphics libraries, have been written in C, and therefore access to them presented a portability problem. This has been addressed by incorporation of C interoperability into the 2003 standard.

It is now possible (and relatively easy) to write an entirely portable program in Fortran, even without recourse to a preprocessor.

Variants of Fortran

pecific variants

Vendors of high-performance scientific computers ("e.g.," Burroughs, CDC, Cray, Honeywell, IBM, Texas Instruments, and UNIVAC) added extensions to Fortran to take advantage of special hardware features such as instruction cache, CPU pipelines, and vector arrays. For example, one of IBM's FORTRAN compilers ("H Extended IUP") had a level of optimization which reordered the machine language instructions to keep multiple internal arithmetic units busy simultaneously. Another example is "CFD", a special variant of Fortran designed specifically for the ILLIAC IV supercomputer, running at NASA's Ames Research Center.IBM Research Labs also developed an extended FORTRAN-based language called "VECTRAN"for processing of vectors and matricies.

Object-Oriented Fortran was an object-oriented extension of Fortran, in which data items can be grouped into objects, which can be instantiated and executed in parallel. It was available for Sun, Iris, iPSC, and nCUBE, but is no longer supported.

Such machine-specific extensions have either disappeared over time or have had elements incorporated into the main standards; the major remaining extension is OpenMP, which is a cross-platform extension for shared memory programming. One new extension, CoArray Fortran, is intended to support parallel programming.

FOR TRANSIT for the IBM 650

"FOR TRANSIT" was the name of a reduced version of the IBM 704 FORTRAN language, which was implemented for the IBM 650, using a translator program developed at Carnegie ["Internal Translator (IT) A Compiler for the IBM 650", by A. J. Perlis, J. W. Smith, and H. R. Van Zoeren, Computation Center,Carnegie Institute of Technology ] in the late 1950s.The following comment appears in the IBM Reference Manual ("FOR TRANSIT Automatic Coding System" C28-4038, Copyright 1957, 1959 by IBM):

The FORTRAN system was designed for a more complexmachine than the 650, and consequently some of the 32 statements found in the FORTRAN Programmer's Reference Manual are notacceptable to the FOR TRANSIT system. In addition, certainrestrictions to the FORTRAN language have been added. However,none of these restrictions make a source program written for FOR TRANSIT incompatible with the FORTRAN system for the 704.

The permissible statements were:: Arithmetic assignment statements, e.g. a = b: GO to n: GO TO (n₁, n₂, ..., n_m), i: IF (a) n₁, n₂, n₃: PAUSE: STOP: DO n i = m1, m2: CONTINUE: END: READ n, list: PUNCH n, list: DIMENSION V, V, V, ...: EQUIVALENCE (a,b,c), (d,c), ...Up to ten subroutines could be used in one program.

FOR TRANSIT statements were limited to columns 7 thru 56, only.Punched cards were used for input and output on the IBM 650. Three passes were required to translate source code to the "IT" language, then to compile the IT statements into SOAP assembly language, and finally to produce the object program, which could then be loaded into the machine to run the program (using punched cards for data input, and outputting results onto punched cards.)

Two versions existed for the 650s with a 2000 word memory drum: FOR TRANSIT I (S) and FOR TRANSIT II, the latter for machines equipped with indexing registers and automatic floating point decimal (bi-quinary) arithmetic. Appendix A of the manual included wiring diagrams for the IBM 533 control panel.

Fortran-based languages

Prior to FORTRAN 77, a number of preprocessors were commonly used to provide a friendlier language, with the advantage that the preprocessed code could be compiled on any machine with a standard FORTRAN compiler. Popular preprocessors included FLECS, MORTRAN, Ratfor, and Ratfiv. (Ratfor and Ratfiv, for example, implemented a remarkably C-like language, outputting preprocessed code in standard FORTRAN 66. [This is not altogether surprising, as Brian Kernighan, one of the co-creators of Ratfor, is also co-author of "The C Programming Language".] )

The Fortran-95 Standard includes an optional "Part 3" which defines an optional conditional compilation capability. This capability is often referred to as "CoCo".

Many Fortran compilers have integrated subsets of the C preprocessor into their systems.

SIMSCRIPT is an application specific Fortran preprocessor for modeling and simulating large discrete systems.

F (programming language) was designed to be a clean subset of Fortran 95 that attempted to remove the redundant, unstructured, and deprecated features of Fortran, such as the EQUIVALENCE statement. F retains the array features added in Fortran 90, and removes control statements that were obsoleted by structured programming constructs added both Fortran 77 and Fortran 90. F is described by its creators as "a compiled, structured, array programming language especially well suited to education and scientific computing." cite web | url=http://www.fortran.com/F/index.html | title= F Programming Language Homepage)

Code examples

The sample programs can be compiled and run with any standard Fortran compiler (see the end of this article for lists of compilers). Most modern Fortran compilers expect a file with a .f or .for extension (for FORTRAN 66 or FORTRAN 77 fixed-form source, although the FORTRAN 66 dialect may have to be selected specifically with a command-line option) or .f90/.f95 extension (for Fortran 90/95 free-form source, respectively).

FORTRAN quotations

For a programming language with a half-century legacy, FORTRAN not surprisingly has accumulated its share of jokes and folklore.

From the historical record

* "God is Real, unless declared Integer." J. Allan Toogood, FORTRAN programmer [From . In FORTRAN, undeclared variables can be typed according to their first letter, so "God" would be a real variable, under default implicit typing rules.]

* "FORTRAN—the "infantile disorder"—, by now nearly 20 years old, is hopelessly inadequate for whatever computer application you have in mind today: it is now too clumsy, too risky, and too expensive to use." —Edsger Dijkstra, 1975cite news | url=http://www.cs.utexas.edu/users/EWD/transcriptions/EWD04xx/EWD498.html | last=Dijkstra | first=E.W | title=How do we tell truths that might hurt? | date=1975-06-18 | accessdate=2008-08-20]

* "The sooner the world forgets that FORTRAN ever existed, the better." (imputed to Joseph Weizenbaum)

* "95 percent of the people who programmed in the early years would never have done it without Fortran." — Ken Thompson, circa 2005cite news | url=http://www.nytimes.com/2007/03/19/obituaries/20cnd-backus.html?ex=1332043200&en=adde3ee5a1875330&ei=5124&partner=permalink&exprod=permalink | title=John W. Backus, 82, Fortran Developer, Dies | accessdate=2007-03-20 | last=Lohr | first=Steve | date=2007-03-19]

* "The primary purpose of the DATA statement is to give names to constants; instead of referring to pi as 3.141592653589793 at every appearance, the variable PI can be given that value with a DATA statement and used instead of the longer form of the constant. This also simplifies modifying the program, should the value of pi change." —Early FORTRAN manual for Xerox Computers [Prior to FORTRAN 77, which standardised the PARAMETER statement (the preferred method of defining constants first seen in UNIVAC FORTRAN V), the DATA statement was the conventional way to define constants, although this statement merely specified initial values and did not prevent the corresponding variables from being modified (as by regular assignment statements).]

* "Consistently separating words by spaces became a general custom about the tenth century A.D., and lasted until about 1957, when FORTRAN abandoned the practice." —"Sun FORTRAN Reference Manual"

* "People are very flexible and learn to adjust to strange surroundings — they can become accustomed to read Lisp and Fortran programs, for example." —"Art of PROLOG", Leon Sterling and Ehud Shapiro, MIT Press

* "Warning: Go directly to Jail. Do not pass GO. Do not collect $200." — Easter egg in the SDS/Xerox Sigma 7 FORTRAN compiler, when the statement GO TO JAIL was encountered. The message is from a Chance card in Monopoly.

* "A computer without COBOL and FORTRAN is like a piece of chocolate cake without ketchup or mustard." — a fortune cookie from the Unix program fortune.

* "The determined Real Programmer can write FORTRAN programs in any language." — "Real Programmers Don't Use Pascal", Ed Post, 1982

References in popular culture

* In the pilot episode of the "Futurama" series, the robot Bender drinks a bottle of "Olde FORTRAN Malt Liquor" (alluding to "Olde English" malt liquor)

* Computer folklore has incorrectly attributed the loss of the Mariner 1 space probe to a syntax error in a Fortran program. For example, "Recall the first American space probe to Venus, reportedly lost because Fortran cannot recognize a missing comma in a DO statement…" [cite book |last = Hoare |first = C. A. R. |title = Hints on Programming Language Design in cite book | title = Sigact/Sigplan Symposium on Principles of Programming Languages |month=October | year=1973, reprinted in cite book |last = Horowitz |title = Programming Languages, A Grand Tour, 3rd ed. See [http://catless.ncl.ac.uk/Risks/9.54.html#subj1 Risks Digest: "Mariner 1", Vol. 9: Iss. 54, 12 Dec 89] (and [http://catless.ncl.ac.uk/Risks/8.75.html#subj1 Risks Digest: "Mariner I -- no holds BARred", Vol. 8: Iss. 75] , for what really happened] )] .
* In 1982, 10,000 Maniacs released a song named "" that includes the repeated line — "Science [is] truth for life, in Fortran tongue the answer".

Letter O considered harmful

During the same Fortran Standards Committee meeting at which the name "FORTRAN 77" was chosen, a technical proposal was somehow smuggled into the official distribution, bearing the title, "Letter O considered harmful".This deceptively simple proposal purported to address the confusion that sometimes arises between the letter "O" and the numeral zero, by eliminating the letter from allowable variable names.However, the method proposed was to eliminate the letter from the character set entirely (thereby retaining 48 as the number of lexical characters, which the colon had increased to 49).

Among the "PRO" arguments was the assertion that this would also promote structured programming, by making it impossible to use the notorious GO TO statement as before. (Troublesome FORMAT statements would be eliminated, as well.)

The sole "CON" argument conceded that "this might invalidate some existing programs" but noted that most of these "probably were non-conforming, anyway". [X3J3 post-meeting distribution for meeting held at Brookhaven National Laboratory in November 1976.]

References

Textbooks

* cite book
first = Ed
last = Akin
year = 2003
title = Object Oriented Programming via Fortran 90/95
edition = 1st ed.
publisher = Cambridge University Press
id = ISBN 0-521-52408-3

* cite book
first = D. M.
last = Etter
year = 1990
title = Structured FORTRAN 77 for Engineers and Scientists
edition = 3rd ed.
publisher = The Benjamin/Cummings Publishing Company, Inc.
id = ISBN 0-8053-0051-1

* cite book
first = Stephen J.
last = Chapman
year = 2007
title = Fortran 95/2003 for Scientists and Engineers
edition = 3rd ed.
publisher = McGraw-Hill
id = ISBN 978-0-07-319157-7

* cite book
first = Stephen J.
last = Chapman
year = 2003
title = Fortran 90/95 for Scientists and Engineers
edition = 2nd ed.
publisher = McGraw-Hill
id = ISBN 0-07-282575-8
* cite book
first = Ian
last = Chivers
coauthors = Jane Sleightholme
year = 2006
title = Introduction to Programming with Fortran
edition = 1st ed.
publisher = Springer
id = ISBN 1-84628-053-2
* cite book
first = T. M. R.
last = Ellis
coauthors = Ivor R. Phillips, Thomas M. Lahey
year = 1994
title = Fortran 90 Programming
edition = 1st ed.
publisher = Addison Wesley
id = ISBN 0-201-54446-6
* cite book
first = Michael
last = Kupferschmid
year = 2002
title = Classical Fortran: Programming for Engineering and Scientific Applications
publisher = Marcel Dekker (CRC Press)
id = ISBN 0-8247-0802-4
* cite book
first = Daniel D.
last = McCracken
year = 1961
title = A Guide to Fortran Programming
publisher = Wiley
* cite book
first = Daniel D.
last = McCracken
year = 1965
title = A Guide to Fortran IV Programming
publisher = Wiley
* cite book
first = Michael
last = Metcalf
coauthors = John Reid, Malcolm Cohen
year = 2004
title = Fortran 95/2003 Explained
publisher = Oxford University Press
id = ISBN 0-19-852693-8
* cite book
first = Larry
last = Nyhoff
coauthors = Sanford Leestma
year = 1995
title = FORTRAN 77 for Engineers and Scientists with an Introduction to Fortran 90
edition = 4th ed.
publisher = Prentice Hall
id = ISBN 0-13-363003-X
* cite book
first = Rudnei Dias
last = da Cunha
year = 2005
title = Introdução à Linguagem de Programação Fortran 90
publisher = Editora da Universidade Federal do Rio Grande do Sul
id = ISBN 85-7025-829-1
* cite book
first = Javier
last = Martínez Baena
coauthors = Ignario Requena Ramos, Nicolás Marín Ruiz
year = 2006
title = Programación estructurada con Fortran 90/95
publisher = Universidad de Granada
id = ISBN 84-338-3923-3

"Core" language standards

* cite book
last = ANSI X3.9-1966
title = USA Standard FORTRAN
edition = informally known as FORTRAN 66
publisher = American National Standards Institute
* cite book
last = ANSI X3.9-1978
title = American National Standard – Programming Language FORTRAN
edition = also known as ISO 1539-1980, informally known as FORTRAN 77
publisher = American National Standards Institute
* cite book
last = ANSI X3.198-1992 (R1997)
title = American National Standard – Programming Language Fortran Extended
edition = informally known as Fortran 90
publisher = American National Standards Institute
* cite book
last = ISO/IEC 1539-1:1997
title = Information technology – Programming languages – Fortran – Part 1: Base language
edition = informally known as Fortran 95. There are a further two parts to this standard. Part 1 has been formally adopted by ANSI
* cite book
last = ISO/IEC 1539-1:2004
title = Information technology – Programming languages – Fortran – Part 1: Base language
edition = informally known as Fortran 2003

Related standards

* cite journal
author = Wilfried Kneis
title = Draft standard Industrial Real-Time FORTRAN
journal = ACM SIGPLAN Notices
month = October | year = 1981
volume = 16
issue = 7
pages = 45–60
publisher = ACM Press
doi = 10.1145/947864.947868
* cite book
last = MIL-STD-1753
title = DoD Supplement to X3.9-1978
publisher = U. S. Government Printing Office
* cite book
last = POSIX 1003.9-1992
title = POSIX FORTRAN 77 Language Interface – Part 1: Binding for System Application Program Interface [API]
url = http://standards.ieee.org/reading/ieee/std_public/description/posix/1003.9-1992_desc.html
publisher = The Institute of Electrical and Electronics Engineers, Inc
* ISO 8651-1:1988 "Information processing systems -- Computer graphics -- Graphical Kernel System (GKS) language bindings -- Part 1: FORTRAN"

Notes

See also

* Alphabetical list of programming languages

External links

History
* [http://web.mit.edu/6.035/www/papers/BackusEtAl-FortranAutomaticCodingSystem-1957.pdf "The FORTRAN Automatic Coding System"] (1.39 MiB) — 1957 copy describes the design and implementation of the first FORTRAN compiler by the IBM team
* [http://www.fh-jena.de/~kleine/history/ Early Fortran manuals] and [http://www.fh-jena.de/~kleine/history/languages/FortranAutomaticCodingSystemForTheIBM704.pdf The very first Fortran manual, by John Backus] (6.11 MiB) dated [1956-10-15]
* [http://community.computerhistory.org/scc/projects/FORTRAN/ History of FORTRAN] and [http://community.computerhistory.org/scc/projects/FORTRAN/FORTRAN_Systems_Manual-1960.pdf Systems Manual for 704/ /709 FORTRAN] (13.5 MiB)
* [http://hopl.murdoch.edu.au/showlanguage.prx?exp=8&language=FORTRAN FORTRAN at HOPL site]
* [http://bitsavers.org/pdf/ibm/704/R23-9518-0-1_FORTRAN_CE_Manual_1959.pdf "The IBM CE Manual for FORTRAN I, II, and 709"] from 1959 (3.82 MiB)
* [http://www.research.ibm.com/journal/rd/255/ibmrd2505Q.pdf "A History of Language Processor Technology in IBM"] (1.45 MiB) — by F.E. Allen, IBM Journal of Research and Development, v.25, no.5, September 1981

Standards
* [http://gcc.gnu.org/wiki/GFortranStandards Comprehensive Fortran Standards Documents] by GFortran
* [http://www.nag.co.uk/sc22wg5/ JTC1/SC22/WG5] — The ISO/IEC Fortran Working Group
* [http://www.fortran.com/fortran/F77_std/rjcnf.html ANSI(R) X3.9-1978] Fortran 77 Standard
** [http://www.fortran.com/fortran/mil_std_1753.html MIL-STD 1753] DoD Extensions to Fortran 77
* [http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=17366 ISO/IEC 1539:1991] Fortran 90 Standard
* [http://j3-fortran.org/doc/standing/archive/007/97-007r2/pdf/97-007r2.pdf final draft] Fortran 95 Standard
* [http://www.dkuug.dk/jtc1/sc22/open/n3661.pdf WG5 (2003) ISO/IEC JTC1/SC22/WG5 N1578] Final Committee Draft of Fortran 2003 standardTutorials
* [http://www.star.le.ac.uk/%7Ecgp/prof77.pdf "Professional Programmer's Guide to FORTRAN 77"] (493 KiB) — Guide written by Clive G. Page of the University of Leicester
* [http://www.aspire.cs.uah.edu/textbook/index_f77.html Unit 7.1 FORTRAN 77] and [http://www.aspire.cs.uah.edu/textbook/index_f90.html Unit 7.2 Fortran 90] — Part of ASPIRE's "Computational Science Textbook" project
* [http://www.ibiblio.org/pub/languages/fortran/unfp.html "User Notes on FORTRAN Programming (UNFP)] — An open cooperative guide

References
* [http://rsusu1.rnd.runnet.ru/develop/fortran/prof77/prof77.html The Professional Programmer's Guide to FORTRAN 77]
* [http://www.fortranplus.co.uk/fortran_info.html Fortran 77, 90, 95, 2003 Information & Resources]
* [http://home.casema.nl/fam.engelberts/ Fortran 77] — FORTRAN 77 documentation
* [http://www.physics.ucdavis.edu/~vem/F77_Ref.pdf Fortran 77 4.0 Reference Manual] (851 KiB)

Code repositories
* [http://www.nag.co.uk/nagware/Examples.asp Fortran 90 Software Repository] — Numerical Algorithms Group
* [http://crd.lbl.gov/~dhbailey/mpdist/index.html High-Precision Software Directory] — Computational Research Division of Lawrence Berkeley National Laboratory
* [http://www.nhse.org/ National HPCC Software Exchange] (defunct) Department of Computer Science at the University of Tennessee at Knoxville
* [http://www.netlib.org/ Netlib Repository] at the University of Tennessee at Knoxville and Oak Ridge National Laboratory
* [http://users.bigpond.net.au/amiller/ Software from Alan J. Miller] Logistic Regression, TOMS algorithms, Special code for F, Applied Statistics Algorithms and NAS compilers

Open source compilers
* [http://gcc.gnu.org/wiki/GFortran GFortran] — The GNU Fortran compiler, part of GCC. Distributed as part of GCC as of GCC 4.0. Replaced g77.
* [http://www.g95.org/ g95] — Free, open source Fortran 95 compiler and runtime libraries
* [http://www.open64.net Open64] — Open Research Compiler. Suite of optimizing compiler development tools for Intel Itanium (Linux)
* [http://www.openwatcom.org/ Open Watcom] — A joint effort between SciTech Software Inc, Sybase and the Open Source development community to maintain Fortran cross compilers and tools

Non-open source compilers
* Intel Fortran Compiler
* [http://www.absoft.com Absoft] Fortran 95/90/77 and C/C++ compilers for Windows, Mac OS 9 and OS X, Linux IA32 and AMD Opteron and AMD Athlon 64-bit processors
* [http://www-306.ibm.com/software/awdtools/fortran/ IBM] Fortran 95 compilers for AIX, Blue Gene, and Linux
* [http://www.lahey.com Lahey/Fujitsu] — Fortran 95 compilers for Linux and Windows
* [http://www.nag.co.uk/nagware/np.asp NAGWare] Fortran 95 compiler with 2003 features for Linux, Windows, and Unix on many platforms
* [http://pathscale.com/ekopath.html Qlogic Pathscale] — Fortran 95, C, and C++ compilers for Linux on AMD Opteron and Intel 64-bit and 32-bit x86 CPUs
* [http://www.pgroup.com/index.htm PGI] Fortran 95, C and C++ Compilers for 32-bit and 64-bit AMD64 and IA32 processor-based Linux and Windows systems
* [http://www.silverfrost.com/11/ftn95/overview.asp Silverfrost (was Salford)] — Personal edition (Windows)
* Sun Studio Compiler Suite — From Sun Microsystems; compiles optimized and parallelized code for the Solaris OS on SPARC and x86/x64 platforms, and Linux on x86/x64 platforms

Integrated Development Environment
* [http://www.eclipse.org/photran/ Photran] — An IDE for Fortran 77, 90, and 95 based on Eclipse and the CDT.

Graphical libraries/GUI
* [http://www.dislin.de DISLIN] — A high-level plotting library for displaying data as curves, polar plots, bar graphs, pie charts, 3D-color plots, surfaces, contours and maps
* [http://math.nist.gov/f90gl/ f90gl] — Public domain implementation of the official Fortran 90 bindings for OpenGL (Linux, Mac OS X, Solaris, UNIX, Windows)
* [http://wiki.tcl.tk/4004 ftcl] — A Fortran–Tcl/TK interface
* [http://g2.sourceforge.net/ g2 graphical library] — Portable and 2D graphics library (Linux, Mac OS X, OpenVMS, Solaris, UNIX, Windows)GNU LGPL
* [http://spdg1.sci.shizuoka.ac.jp/grwinlib/english/ GrWin Graphics Library] — Free graphics routine library for Fortran (Windows)
* [http://pilib.beta-centauri.de pilib] — Platform Independent Library for Fortran 90/95 (Linux, Mac OS X, UNIX, Windows) GNU LGPL
* [http://plplot.sourceforge.net/ PLplot] — A Scientific Plotting Library (Linux, Mac OS X, MS-DOS, Unix, Windows) GNU LGPL
* [http://www.ancad.com/ MATFOR] — A Scientific Graphical Numerical Library (Linux, Mac OS X, MS-DOS, SuSe, Windows)

Testing Frameworks
* FUnit — a unit testing framework.

Miscellaneous
* [http://groups.google.com/group/comp.lang.fortran comp.lang.fortran] on Usenet
* [http://dmoz.org/Computers/Programming/Languages/Fortran/ Fortran] — Open Directory category
* [http://www.atkielski.com/PDF/data/fortran.pdf FORTRAN Coding form] (41.2 KiB)
* [http://www.neuralwiki.org/index.php?title=Installing_Fortran Fortran (G77 and Gfortran) installation and configuration guide for Windows operating system]
* [http://kgptech.blogspot.com/2005/07/fortran_14.html Fortran Tutorial Links]