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fort77 — FORTRAN compiler (FORTRAN)


fort77 [−c] [−g] [−L directory]... [−O optlevel] [−o outfile] [−s]
[−w] operand...


The fort77 utility is the interface to the FORTRAN compilation system; it shall accept the
full FORTRAN-77 language defined by the ANSI X3.9‐1978 standard. The system conceptually
consists of a compiler and link editor. The files referenced by operands are compiled and
linked to produce an executable file. It is unspecified whether the linking occurs
entirely within the operation of fort77; some implementations may produce objects that are
not fully resolved until the file is executed.

If the −c option is present, for all pathname operands of the form file.f, the files:

$(basename pathname.f).o

shall be created or overwritten as the result of successful compilation. If the −c option
is not specified, it is unspecified whether such .o files are created or deleted for the
file.f operands.

If there are no options that prevent link editing (such as −c) and all operands compile
and link without error, the resulting executable file shall be written into the file named
by the −o option (if present) or to the file a.out. The executable file shall be created
as specified in the System Interfaces volume of POSIX.1‐2008, except that the file
permissions shall be set to: S_IRWXO | S_IRWXG | S_IRWXU

and that the bits specified by the umask of the process shall be cleared.


The fort77 utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section
12.2, Utility Syntax Guidelines, except that:

* The −l library operands have the format of options, but their position within a list
of operands affects the order in which libraries are searched.

* The order of specifying the multiple −L options is significant.

* Conforming applications shall specify each option separately; that is, grouping option
letters (for example, −cg) need not be recognized by all implementations.

The following options shall be supported:

−c Suppress the link-edit phase of the compilation, and do not remove any object
files that are produced.

−g Produce symbolic information in the object or executable files; the nature of
this information is unspecified, and may be modified by implementation-defined
interactions with other options.

−s Produce object or executable files, or both, from which symbolic and other
information not required for proper execution using the exec family of functions
defined in the System Interfaces volume of POSIX.1‐2008 has been removed
(stripped). If both −g and −s options are present, the action taken is

−o outfile
Use the pathname outfile, instead of the default a.out, for the executable file
produced. If the −o option is present with −c, the result is unspecified.

−L directory
Change the algorithm of searching for the libraries named in −l operands to look
in the directory named by the directory pathname before looking in the usual
places. Directories named in −L options shall be searched in the specified
order. At least ten instances of this option shall be supported in a single
fort77 command invocation. If a directory specified by a −L option contains a
file named libf.a, the results are unspecified.

−O optlevel
Specify the level of code optimization. If the optlevel option-argument is the
digit '0', all special code optimizations shall be disabled. If it is the digit
'1', the nature of the optimization is unspecified. If the −O option is omitted,
the nature of the system's default optimization is unspecified. It is
unspecified whether code generated in the presence of the −O 0 option is the
same as that generated when −O is omitted. Other optlevel values may be

−w Suppress warnings.

Multiple instances of −L options can be specified.


An operand is either in the form of a pathname or the form −l library. At least one
operand of the pathname form shall be specified. The following operands shall be

file.f The pathname of a FORTRAN source file to be compiled and optionally passed to
the link editor. The filename operand shall be of this form if the −c option is

file.a A library of object files typically produced by ar, and passed directly to the
link editor. Implementations may recognize implementation-defined suffixes other
than .a as denoting object file libraries.

file.o An object file produced by fort77 −c and passed directly to the link editor.
Implementations may recognize implementation-defined suffixes other than .o as
denoting object files.

The processing of other files is implementation-defined.

−l library
(The letter ell.) Search the library named:


A library is searched when its name is encountered, so the placement of a −l
operand is significant. Several standard libraries can be specified in this
manner, as described in the EXTENDED DESCRIPTION section. Implementations may
recognize implementation-defined suffixes other than .a as denoting libraries.


Not used.


The input file shall be one of the following: a text file containing FORTRAN source code;
an object file in the format produced by fort77 −c; or a library of object files, in the
format produced by archiving zero or more object files, using ar. Implementations may
supply additional utilities that produce files in these formats. Additional input files
are implementation-defined.

A <tab> encountered within the first six characters on a line of source code shall cause
the compiler to interpret the following character as if it were the seventh character on
the line (that is, in column 7).


The following environment variables shall affect the execution of fort77:

LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of POSIX.1‐2008, Section 8.2,
Internationalization Variables for the precedence of internationalization
variables used to determine the values of locale categories.)

LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.

LC_CTYPE Determine the locale for the interpretation of sequences of bytes of text data
as characters (for example, single-byte as opposed to multi-byte characters in
arguments and input files).

Determine the locale that should be used to affect the format and contents of
diagnostic messages written to standard error.

NLSPATH Determine the location of message catalogs for the processing of LC_MESSAGES.

TMPDIR Determine the pathname that should override the default directory for temporary
files, if any.




Not used.


The standard error shall be used only for diagnostic messages. If more than one file
operand ending in .f (or possibly other unspecified suffixes) is given, for each such

"%s:\n", <file>

may be written to allow identification of the diagnostic message with the appropriate
input file.

This utility may produce warning messages about certain conditions that do not warrant
returning an error (non-zero) exit value.


Object files, listing files, and executable files shall be produced in unspecified


Standard Libraries
The fort77 utility shall recognize the following −l operand for the standard library:

−l f This library contains all functions referenced in the ANSI X3.9‐1978 standard.
This operand shall not be required to be present to cause a search of this

In the absence of options that inhibit invocation of the link editor, such as −c, the
fort77 utility shall cause the equivalent of a −l f operand to be passed to the link
editor as the last −l operand, causing it to be searched after all other object files and
libraries are loaded.

It is unspecified whether the library libf.a exists as a regular file. The implementation
may accept as −l operands names of objects that do not exist as regular files.

External Symbols
The FORTRAN compiler and link editor shall support the significance of external symbols up
to a length of at least 31 bytes; case folding is permitted. The action taken upon
encountering symbols exceeding the implementation-defined maximum symbol length is

The compiler and link editor shall support a minimum of 511 external symbols per source or
object file, and a minimum of 4095 external symbols total. A diagnostic message is written
to standard output if the implementation-defined limit is exceeded; other actions are


The following exit values shall be returned:

0 Successful compilation or link edit.

>0 An error occurred.


When fort77 encounters a compilation error, it shall write a diagnostic to standard error
and continue to compile other source code operands. It shall return a non-zero exit
status, but it is implementation-defined whether an object module is created. If the link
edit is unsuccessful, a diagnostic message shall be written to standard error, and fort77
shall exit with a non-zero status.

The following sections are informative.




The following usage example compiles xyz.f and creates the executable file foo:

fort77 −o foo xyz.f

The following example compiles xyz.f and creates the object file xyz.o:

fort77 −c xyz.f

The following example compiles xyz.f and creates the executable file a.out:

fort77 xyz.f

The following example compiles xyz.f, links it with b.o, and creates the executable a.out:

fort77 xyz.f b.o


The name of this utility was chosen as fort77 to parallel the renaming of the C compiler.
The name f77 was not chosen to avoid problems with historical implementations. The
ANSI X3.9‐1978 standard was selected as a normative reference because the ISO/IEC version
of FORTRAN-77 has been superseded by the ISO/IEC 1539:1991 standard.

The file inclusion and symbol definition #define mechanisms used by the c99 utility were
not included in this volume of POSIX.1‐2008—even though they are commonly implemented—
since there is no requirement that the FORTRAN compiler use the C preprocessor.

The −onetrip option was not included in this volume of POSIX.1‐2008, even though many
historical compilers support it, because it is derived from FORTRAN-66; it is an
anachronism that should not be perpetuated.

Some implementations produce compilation listings. This aspect of FORTRAN has been left
unspecified because there was controversy concerning the various methods proposed for
implementing it: a −V option overlapped with historical vendor practice and a naming
convention of creating files with .l suffixes collided with historical lex file naming

There is no −I option in this version of this volume of POSIX.1‐2008 to specify a
directory for file inclusion. An INCLUDE directive has been a part of the Fortran-90
discussions, but an interface supporting that standard is not in the current scope.

It is noted that many FORTRAN compilers produce an object module even when compilation
errors occur; during a subsequent compilation, the compiler may patch the object module
rather than recompiling all the code. Consequently, it is left to the implementor whether
or not an object file is created.

A reference to MIL-STD-1753 was removed from an early proposal in response to a request
from the POSIX FORTRAN-binding standard developers. It was not the intention of the
standard developers to require certification of the FORTRAN compiler, and
IEEE Std 1003.9‐1992 does not specify the military standard or any special preprocessing
requirements. Furthermore, use of that document would have been inappropriate for an
international standard.

The specification of optimization has been subject to changes through early proposals. At
one time, −O and −N were Booleans: optimize and do not optimize (with an unspecified
default). Some historical practice led this to be changed to:

−O 0 No optimization.

−O 1 Some level of optimization.

−O n Other, unspecified levels of optimization.

It is not always clear whether ``good code generation'' is the same thing as optimization.
Simple optimizations of local actions do not usually affect the semantics of a program.
The −O 0 option has been included to accommodate the very particular nature of scientific
calculations in a highly optimized environment; compilers make errors. Some degree of
optimization is expected, even if it is not documented here, and the ability to shut it
off completely could be important when porting an application. An implementation may treat
−O 0 as ``do less than normal'' if it wishes, but this is only meaningful if any of the
operations it performs can affect the semantics of a program. It is highly dependent on
the implementation whether doing less than normal is logical. It is not the intent of the
−O 0 option to ask for inefficient code generation, but rather to assure that any
semantically visible optimization is suppressed.

The specification of standard library access is consistent with the C compiler
specification. Implementations are not required to have /usr/lib/libf.a, as many
historical implementations do, but if not they are required to recognize f as a token.

External symbol size limits are in normative text; conforming applications need to know
these limits. However, the minimum maximum symbol length should be taken as a constraint
on a conforming application, not on an implementation, and consequently the action taken
for a symbol exceeding the limit is unspecified. The minimum size for the external symbol
table was added for similar reasons.

The CONSEQUENCES OF ERRORS section clearly specifies the behavior of the compiler when
compilation or link-edit errors occur. The behavior of several historical implementations
was examined, and the choice was made to be silent on the status of the executable, or
a.out, file in the face of compiler or linker errors. If a linker writes the executable
file, then links it on disk with lseek()s and write()s, the partially linked executable
file can be left on disk and its execute bits turned off if the link edit fails. However,
if the linker links the image in memory before writing the file to disk, it need not touch
the executable file (if it already exists) because the link edit fails. Since both
approaches are historical practice, a conforming application shall rely on the exit status
of fort77, rather than on the existence or mode of the executable file.

The −g and −s options are not specified as mutually-exclusive. Historically, these two
options have been mutually-exclusive, but because both are so loosely specified, it seemed
appropriate to leave their interaction unspecified.

The requirement that conforming applications specify compiler options separately is to
reserve the multi-character option name space for vendor-specific compiler options, which
are known to exist in many historical implementations. Implementations are not required to
recognize, for example, −gc as if it were −g −c; nor are they forbidden from doing so. The
SYNOPSIS shows all of the options separately to highlight this requirement on

Echoing filenames to standard error is considered a diagnostic message because it would
otherwise be difficult to associate an error message with the erring file. They are
described with ``may'' to allow implementations to use other methods of identifying files
and to parallel the description in c99.


A compilation system based on the ISO/IEC 1539:1991 standard may be considered for a
future version; it may have a different utility name from fort77.

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