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G77(1)				      GNU				G77(1)

       g77 - GNU project Fortran 77 compiler

       g77 [-c|-S|-E]
	   [-g]	[-pg] [-Olevel]
	   [-Wwarn...] [-pedantic]
	   [-Idir...] [-Ldir...]
	   [-Dmacro[=defn]...] [-Umacro]
	   [-foption...] [-mmachine-option...]
	   [-o outfile]	infile...

       Only the	most useful options are	listed here; see below for the remain-

       The g77 command supports	all the	options	supported by the gcc command.

       All gcc and g77 options are accepted both by g77	and by gcc (as well as
       any other drivers built at the same time, such as g++), since adding
       g77 to the gcc distribution enables acceptance of g77 options by	all of
       the relevant drivers.

       In some cases, options have positive and	negative forms;	the negative
       form of -ffoo would be -fno-foo.	 This manual documents only one	of
       these two forms,	whichever one is not the default.

       Here is a summary of all	the options specific to	GNU Fortran, grouped
       by type.	 Explanations are in the following sections.

       Overall Options
	   -fversion  -fset-g77-defaults  -fno-silent

       Shorthand Options
	   -ff66  -fno-f66  -ff77  -fno-f77  -fno-ugly

       Fortran Language	Options
	   -ffree-form	-fno-fixed-form	 -ff90 -fvxt  -fdollar-ok  -fno-back-
	   slash -fno-ugly-args	 -fno-ugly-assign  -fno-ugly-assumed
	   -fugly-comma	 -fugly-complex	 -fugly-init  -fugly-logint -fonetrip
	   -ftypeless-boz -fintrin-case-initcap	 -fintrin-case-upper -fin-
	   trin-case-lower  -fintrin-case-any -fmatch-case-initcap
	   -fmatch-case-upper -fmatch-case-lower  -fmatch-case-any
	   -fsource-case-upper	-fsource-case-lower -fsource-case-preserve
	   -fsymbol-case-initcap  -fsymbol-case-upper -fsymbol-case-lower
	   -fsymbol-case-any -fcase-strict-upper  -fcase-strict-lower
	   -fcase-initcap  -fcase-upper	 -fcase-lower  -fcase-preserve
	   -ff2c-intrinsics-delete  -ff2c-intrinsics-hide -ff2c-intrin-
	   sics-disable	 -ff2c-intrinsics-enable -fbadu77-intrinsics-delete
	   -fbadu77-intrinsics-hide -fbadu77-intrinsics-disable
	   -fbadu77-intrinsics-enable -ff90-intrinsics-delete  -ff90-intrin-
	   sics-hide -ff90-intrinsics-disable  -ff90-intrinsics-enable
	   -fgnu-intrinsics-delete  -fgnu-intrinsics-hide -fgnu-intrin-
	   sics-disable	 -fgnu-intrinsics-enable -fmil-intrinsics-delete
	   -fmil-intrinsics-hide -fmil-intrinsics-disable  -fmil-intrin-
	   sics-enable -funix-intrinsics-delete	 -funix-intrinsics-hide
	   -funix-intrinsics-disable  -funix-intrinsics-enable -fvxt-intrin-
	   sics-delete	-fvxt-intrinsics-hide -fvxt-intrinsics-disable
	   -fvxt-intrinsics-enable -ffixed-line-length-n

       Warning Options
	   -fsyntax-only  -pedantic  -pedantic-errors  -fpedantic -w
	   -Wno-globals	 -Wimplicit  -Wunused  -Wuninitialized -Wall  -Wsur-
	   prising -Werror  -W

       Debugging Options

       Optimization Options
	   -malign-double -ffloat-store	 -fforce-mem  -fforce-addr
	   -fno-inline -ffast-math  -fstrength-reduce  -frerun-cse-after-loop
	   -funsafe-math-optimizations -fno-trapping-math -fexpensive-opti-
	   mizations  -fdelayed-branch -fschedule-insns	 -fschedule-insn2
	   -fcaller-saves -funroll-loops  -funroll-all-loops
	   -fno-move-all-movables  -fno-reduce-all-givs	-fno-rerun-loop-opt

       Directory Options
	   -Idir  -I-

       Code Generation Options
	   -fno-automatic  -finit-local-zero  -fno-f2c -ff2c-library
	   -fno-underscoring  -fno-ident -fpcc-struct-return
	   -freg-struct-return -fshort-double  -fno-common  -fpack-struct
	   -fzeros  -fno-second-underscore -femulate-complex -falias-check
	   -fargument-alias -fargument-noalias	-fno-argument-noalias-global
	   -fno-globals	 -fflatten-arrays -fbounds-check  -ffor-

       Compilation can involve as many as four stages: preprocessing, code
       generation (often what is really	meant by the term ``compilation''),
       assembly, and linking, always in	that order.  The first three stages
       apply to	an individual source file, and end by producing	an object
       file; linking combines all the object files (those newly	compiled, and
       those specified as input) into an executable file.

       For any given input file, the file name suffix determines what kind of
       program is contained in the file---that is, the language	in which the
       program is written is generally indicated by the	suffix.	 Suffixes spe-
       cific to	GNU Fortran are	listed below.

	   Fortran source code that should not be preprocessed.

	   Such	source code cannot contain any preprocessor directives,	such
	   as "#include", "#define", "#if", and	so on.

	   You can force .f files to be	preprocessed by	cpp by using -x

	   Fortran source code that must be preprocessed (by the C preproces-
	   sor cpp, which is part of GNU CC).

	   Note	that preprocessing is not extended to the contents of files
	   included by the "INCLUDE" directive---the "#include"	preprocessor
	   directive must be used instead.

	   Ratfor source code, which must be preprocessed by the ratfor	com-
	   mand, which is available separately (as it is not yet part of the
	   GNU Fortran distribution).  One version in Fortran, adapted for use
	   with	g77 is at <>	(of uncertain
	   copyright status).  Another,	public domain version in C is at

       UNIX users typically use	the file.f and file.F nomenclature.  Users of
       other operating systems,	especially those that cannot distinguish
       upper-case letters from lower-case letters in their file	names, typi-
       cally use the file.for and file.fpp nomenclature.

       Use of the preprocessor cpp allows use of C-like	constructs such	as
       "#define" and "#include", but can lead to unexpected, even mistaken,
       results due to Fortran's	source file format.  It	is recommended that
       use of the C preprocessor be limited to "#include" and, in conjunction
       with "#define", only "#if" and related directives, thus avoiding	in-
       line macro expansion entirely.  This recommendation applies especially
       when using the traditional fixed	source form.  With free	source form,
       fewer unexpected	transformations	are likely to happen, but use of con-
       structs such as Hollerith and character constants can nevertheless
       present problems, especially when these are continued across multiple
       source lines.  These problems result, primarily,	from differences
       between the way such constants are interpreted by the C preprocessor
       and by a	Fortran	compiler.

       Another example of a problem that results from using the	C preprocessor
       is that a Fortran comment line that happens to contain any characters
       ``interesting'' to the C	preprocessor, such as a	backslash at the end
       of the line, is not recognized by the preprocessor as a comment line,
       so instead of being passed through ``raw'', the line is edited accord-
       ing to the rules	for the	preprocessor.  For example, the	backslash at
       the end of the line is removed, along with the subsequent newline,
       resulting in the	next line being	effectively commented out---unfortu-
       nate if that line is a non-comment line of important code!

       Note: The -traditional and -undef flags are supplied to cpp by default,
       to help avoid unpleasant	surprises.

       This means that ANSI C preprocessor features (such as the # operator)
       aren't available, and only variables in the C reserved namespace	(gen-
       erally, names with a leading underscore)	are liable to substitution by
       C predefines.  Thus, if you want	to do system-specific tests, use, for
       example,	#ifdef __linux__ rather	than #ifdef linux.  Use	the -v option
       to see exactly how the preprocessor is invoked.

       Unfortunately, the -traditional flag will not avoid an error from any-
       thing that cpp sees as an unterminated C	comment, such as:

	       C Some Fortran compilers	accept /* as starting
	       C an inline comment.

       The following options that affect overall processing are	recognized by
       the g77 and gcc commands	in a GNU Fortran installation:

	   Ensure that the g77 version of the compiler phase is	reported, if
	   run,	and, starting in "egcs"	version	1.1, that internal consistency
	   checks in the f771 program are run.

	   This	option is supplied automatically when -v or --verbose is spec-
	   ified as a command-line option for g77 or gcc and when the result-
	   ing commands	compile	Fortran	source files.

	   In GCC 3.1, this is changed back to the behaviour gcc displays for
	   .c files.

	   Version info: This option was obsolete as of	"egcs" version 1.1.
	   The effect is instead achieved by the "lang_init_options" routine
	   in gcc/gcc/f/com.c.

	   Set up whatever gcc options are to apply to Fortran compilations,
	   and avoid running internal consistency checks that might take some

	   This	option is supplied automatically when compiling	Fortran	code
	   via the g77 or gcc command.	The description	of this	option is pro-
	   vided so that users seeing it in the	output of, say,	g77 -v under-
	   stand why it	is there.

	   Also, developers who	run "f771" directly might want to specify it
	   by hand to get the same defaults as they would running "f771" via
	   g77 or gcc However, such developers should, after linking a new
	   "f771" executable, invoke it	without	this option once, e.g. via
	   "./f771 -quiet < /dev/null",	to ensure that they have not intro-
	   duced any internal inconsistencies (such as in the table of intrin-
	   sics) before	proceeding---g77 will crash with a diagnostic if it
	   detects an inconsistency.

	   Print (to "stderr") the names of the	program	units as they are com-
	   piled, in a form similar to that used by popular UNIX f77 implemen-
	   tations and f2c

       Shorthand Options

       The following options serve as ``shorthand'' for	other options accepted
       by the compiler:

	   Note: This option is	no longer supported.  The information, below,
	   is provided to aid in the conversion	of old scripts.

	   Specify that	certain	``ugly'' constructs are	to be quietly
	   accepted.  Same as:

		   -fugly-args -fugly-assign -fugly-assumed
		   -fugly-comma	-fugly-complex -fugly-init

	   These constructs are	considered inappropriate to use	in new or
	   well-maintained portable Fortran code, but widely used in old code.

	   Specify that	all ``ugly'' constructs	are to be noisily rejected.
	   Same	as:

		   -fno-ugly-args -fno-ugly-assign -fno-ugly-assumed
		   -fno-ugly-comma -fno-ugly-complex -fno-ugly-init

	   Specify that	the program is written in idiomatic FORTRAN 66.	 Same
	   as -fonetrip	-fugly-assumed.

	   The -fno-f66	option is the inverse of -ff66.	 As such, it is	the
	   same	as -fno-onetrip	-fno-ugly-assumed.

	   The meaning of this option is likely	to be refined as future	ver-
	   sions of g77	provide	more compatibility with	other existing and
	   obsolete Fortran implementations.

	   Specify that	the program is written in idiomatic UNIX FORTRAN 77
	   and/or the dialect accepted by the f2c product.  Same as -fback-
	   slash -fno-typeless-boz.

	   The meaning of this option is likely	to be refined as future	ver-
	   sions of g77	provide	more compatibility with	other existing and
	   obsolete Fortran implementations.

	   The -fno-f77	option is not the inverse of -ff77.  It	specifies that
	   the program is not written in idiomatic UNIX	FORTRAN	77 or f2c but
	   in a	more widely portable dialect.  -fno-f77	is the same as

	   The meaning of this option is likely	to be refined as future	ver-
	   sions of g77	provide	more compatibility with	other existing and
	   obsolete Fortran implementations.

       Options Controlling Fortran Dialect

       The following options control the dialect of Fortran that the compiler

	   Specify that	the source file	is written in free form	(introduced in
	   Fortran 90) instead of the more-traditional fixed form.

	   Allow certain Fortran-90 constructs.

	   This	option controls	whether	certain	Fortran	90 constructs are rec-
	   ognized.  (Other Fortran 90 constructs might	or might not be	recog-
	   nized depending on other options such as -fvxt, -ff90-intrin-
	   sics-enable,	and the	current	level of support for Fortran 90.)

	   Specify the treatment of certain constructs that have different
	   meanings depending on whether the code is written in	GNU Fortran
	   (based on FORTRAN 77	and akin to Fortran 90)	or VXT Fortran (more
	   like	VAX FORTRAN).

	   The default is -fno-vxt.  -fvxt specifies that the VXT Fortran
	   interpretations for those constructs	are to be chosen.

	   Allow $ as a	valid character	in a symbol name.

	   Specify that	\ is not to be specially interpreted in	character and
	   Hollerith constants a la C and many UNIX Fortran compilers.

	   For example,	with -fbackslash in effect, A\nB specifies three char-
	   acters, with	the second one being newline.  With -fno-backslash, it
	   specifies four characters, A, \, n, and B.

	   Note	that g77 implements a fairly general form of backslash pro-
	   cessing that	is incompatible	with the narrower forms	supported by
	   some	other compilers.  For example, 'A\003B'	is a three-character
	   string in g77 whereas other compilers that support backslash	might
	   not support the three-octal-digit form, and thus treat that string
	   as longer than three	characters.

	   Disallow passing Hollerith and typeless constants as	actual argu-
	   ments (for example, CALL FOO(4HABCD)).

	   Use the same	storage	for a given variable regardless	of whether it
	   is used to hold an assigned-statement label (as in ASSIGN 10	TO I)
	   or used to hold numeric data	(as in I = 3).

	   Assume any dummy array with a final dimension specified as 1	is
	   really an assumed-size array, as if * had been specified for	the
	   final dimension instead of 1.

	   For example,	DIMENSION X(1) is treated as if	it had read DIMENSION

	   In an external-procedure invocation,	treat a	trailing comma in the
	   argument list as specification of a trailing	null argument, and
	   treat an empty argument list	as specification of a single null

	   For example,	CALL FOO(,) is treated as CALL FOO(%VAL(0), %VAL(0)).
	   That	is, two	null arguments are specified by	the procedure call
	   when	-fugly-comma is	in force.  And F = FUNC() is treated as	F =

	   The default behavior, -fno-ugly-comma, is to	ignore a single	trail-
	   ing comma in	an argument list.  So, by default, CALL	FOO(X,)	is
	   treated exactly the same as CALL FOO(X).

	   Do not complain about REAL(expr) or AIMAG(expr) when	expr is	a
	   "COMPLEX" type other	than "COMPLEX(KIND=1)"---usually this is used
	   to permit "COMPLEX(KIND=2)" ("DOUBLE	COMPLEX") operands.

	   The -ff90 option controls the interpretation	of this	construct.

	   Disallow use	of Hollerith and typeless constants as initial values
	   (in "PARAMETER" and "DATA" statements), and use of character	con-
	   stants to initialize	numeric	types and vice versa.

	   For example,	DATA I/'F'/, CHRVAR/65/, J/4HABCD/ is disallowed by

	   Treat "INTEGER" and "LOGICAL" variables and expressions as poten-
	   tial	stand-ins for each other.

	   For example,	automatic conversion between "INTEGER" and "LOGICAL"
	   is enabled, for many	contexts, via this option.

	   Executable iterative	"DO" loops are to be executed at least once
	   each	time they are reached.

	   ANSI	FORTRAN	77 and more recent versions of the Fortran standard
	   specify that	the body of an iterative "DO" loop is not executed if
	   the number of iterations calculated from the	parameters of the loop
	   is less than	1.  (For example, DO 10	I = 1, 0.)  Such a loop	is
	   called a zero-trip loop.

	   Prior to ANSI FORTRAN 77, many compilers implemented	"DO" loops
	   such	that the body of a loop	would be executed at least once, even
	   if the iteration count was zero.  Fortran code written assuming
	   this	behavior is said to require one-trip loops.  For example, some
	   code	written	to the FORTRAN 66 standard expects this	behavior from
	   its "DO" loops, although that standard did not specify this behav-

	   The -fonetrip option	specifies that the source file(s) being	com-
	   piled require one-trip loops.

	   This	option affects only those loops	specified by the (iterative)
	   "DO"	statement and by implied-"DO" lists in I/O statements.	Loops
	   specified by	implied-"DO" lists in "DATA" and specification
	   (non-executable) statements are not affected.

	   Specifies that prefix-radix non-decimal constants, such as Z'ABCD',
	   are typeless	instead	of "INTEGER(KIND=1)".

	   You can test	for yourself whether a particular compiler treats the
	   prefix form as "INTEGER(KIND=1)" or typeless	by running the follow-
	   ing program:

		   R = Z'ABCD1234'
		   J = Z'ABCD1234'
		   IF (J .EQ. I) PRINT *, 'Prefix form is TYPELESS'
		   IF (J .NE. I) PRINT *, 'Prefix form is INTEGER'

	   Reports indicate that many compilers	process	this form as "INTE-
	   GER(KIND=1)", though	a few as typeless, and at least	one based on a
	   command-line	option specifying some kind of compatibility.

	   Specify expected case for intrinsic names.  -fintrin-case-lower is
	   the default.

	   Specify expected case for keywords.	-fmatch-case-lower is the

	   Specify whether source text other than character and	Hollerith con-
	   stants is to	be translated to uppercase, to lowercase, or preserved
	   as is.  -fsource-case-lower is the default.

	   Specify valid cases for user-defined	symbol names.  -fsym-
	   bol-case-any	is the default.

	   Same	as -fintrin-case-upper -fmatch-case-upper -fsource-case-pre-
	   serve -fsymbol-case-upper.  (Requires all pertinent source to be in

	   Same	as -fintrin-case-lower -fmatch-case-lower -fsource-case-pre-
	   serve -fsymbol-case-lower.  (Requires all pertinent source to be in

	   Same	as -fintrin-case-initcap -fmatch-case-initcap
	   -fsource-case-preserve -fsymbol-case-initcap.  (Requires all	perti-
	   nent	source to be in	initial	capitals, as in	Print *,SqRt(Value).)

	   Same	as -fintrin-case-any -fmatch-case-any -fsource-case-upper
	   -fsymbol-case-any.  (Maps all pertinent source to uppercase.)

	   Same	as -fintrin-case-any -fmatch-case-any -fsource-case-lower
	   -fsymbol-case-any.  (Maps all pertinent source to lowercase.)

	   Same	as -fintrin-case-any -fmatch-case-any -fsource-case-preserve
	   -fsymbol-case-any.  (Preserves all case in user-defined symbols,
	   while allowing any-case matching of intrinsics and keywords.	 For
	   example, call Foo(i,I) would	pass two different variables named i
	   and I to a procedure	named Foo.)

	   Specify status of UNIX intrinsics having inappropriate forms.
	   -fbadu77-intrinsics-enable is the default.

	   Specify status of f2c-specific intrinsics.  -ff2c-intrinsics-enable
	   is the default.

	   Specify status of F90-specific intrinsics.  -ff90-intrinsics-enable
	   is the default.

	   Specify status of Digital's COMPLEX-related intrinsics.
	   -fgnu-intrinsics-enable is the default.

	   Specify status of MIL-STD-1753-specific intrinsics.	-fmil-intrin-
	   sics-enable is the default.

	   Specify status of UNIX intrinsics.  -funix-intrinsics-enable	is the

	   Specify status of VXT intrinsics.  -fvxt-intrinsics-enable is the

	   Set column after which characters are ignored in typical fixed-form
	   lines in the	source file, and through which spaces are assumed (as
	   if padded to	that length) after the ends of short fixed-form	lines.

	   Popular values for n	include	72 (the	standard and the default), 80
	   (card image), and 132 (corresponds to ``extended-source'' options
	   in some popular compilers).	n may be none, meaning that the	entire
	   line	is meaningful and that continued character constants never
	   have	implicit spaces	appended to them to fill out the line.
	   -ffixed-line-length-0 means the same	thing as

       Options to Request or Suppress Warnings

       Warnings	are diagnostic messages	that report constructions which	are
       not inherently erroneous	but which are risky or suggest there might
       have been an error.

       You can request many specific warnings with options beginning -W, for
       example -Wimplicit to request warnings on implicit declarations.	 Each
       of these	specific warning options also has a negative form beginning
       -Wno- to	turn off warnings; for example,	-Wno-implicit.	This manual
       lists only one of the two forms,	whichever is not the default.

       These options control the amount	and kinds of warnings produced by GNU

	   Check the code for syntax errors, but don't do anything beyond

	   Issue warnings for uses of extensions to ANSI FORTRAN 77.  -pedan-
	   tic also applies to C-language constructs where they	occur in GNU
	   Fortran source files, such as use of	\e in a	character constant
	   within a directive like #include.

	   Valid ANSI FORTRAN 77 programs should compile properly with or
	   without this	option.	 However, without this option, certain GNU
	   extensions and traditional Fortran features are supported as	well.
	   With	this option, many of them are rejected.

	   Some	users try to use -pedantic to check programs for strict	ANSI
	   conformance.	 They soon find	that it	does not do quite what they
	   want---it finds some	non-ANSI practices, but	not all.  However,
	   improvements	to g77 in this area are	welcome.

	   Like	-pedantic, except that errors are produced rather than warn-

	   Like	-pedantic, but applies only to Fortran constructs.

       -w  Inhibit all warning messages.

	   Inhibit warnings about use of a name	as both	a global name (a sub-
	   routine, function, or block data program unit, or a common block)
	   and implicitly as the name of an intrinsic in a source file.

	   Also	inhibit	warnings about inconsistent invocations	and/or defini-
	   tions of global procedures (function	and subroutines).  Such	incon-
	   sistencies include different	numbers	of arguments and different
	   types of arguments.

	   Warn	whenever a variable, array, or function	is implicitly
	   declared.  Has an effect similar to using the "IMPLICIT NONE"
	   statement in	every program unit.  (Some Fortran compilers provide
	   this	feature	by an option named -u or /WARNINGS=DECLARATIONS.)

	   Warn	whenever a variable is unused aside from its declaration.

	   Warn	whenever an automatic variable is used without first being

	   These warnings are possible only in optimizing compilation, because
	   they	require	data-flow information that is computed only when opti-
	   mizing.  If you don't specify -O, you simply	won't get these	warn-

	   These warnings occur	only for variables that	are candidates for
	   register allocation.	 Therefore, they do not	occur for a variable
	   whose address is taken, or whose size is other than 1, 2, 4 or 8
	   bytes.  Also, they do not occur for arrays, even when they are in

	   Note	that there might be no warning about a variable	that is	used
	   only	to compute a value that	itself is never	used, because such
	   computations	may be deleted by data-flow analysis before the	warn-
	   ings	are printed.

	   These warnings are made optional because GNU	Fortran	is not smart
	   enough to see all the reasons why the code might be correct despite
	   appearing to	have an	error.	Here is	one example of how this	can

		   IF (J.EQ.1) I=1
		   IF (J.EQ.2) I=4
		   IF (J.EQ.3) I=5
		   CALL	FOO(I)

	   If the value	of "J" is always 1, 2 or 3, then "I" is	always ini-
	   tialized, but GNU Fortran doesn't know this.	 Here is another com-
	   mon case:

		   IF (FLAG) VALUE = 9.4

	   This	has no bug because "VALUE" is used only	if it is set.

	   The -Wunused	and -Wuninitialized options combined.  These are all
	   the options which pertain to	usage that we recommend	avoiding and
	   that	we believe is easy to avoid.  (As more warnings	are added to
	   g77 some might be added to the list enabled by -Wall.)

       The remaining -W... options are not implied by -Wall because they warn
       about constructions that	we consider reasonable to use, on occasion, in
       clean programs.

	   Warn	about ``suspicious'' constructs	that are interpreted by	the
	   compiler in a way that might	well be	surprising to someone reading
	   the code.  These differences	can result in subtle, compiler-depen-
	   dent	(even machine-dependent) behavioral differences.  The con-
	   structs warned about	include:

	   o   Expressions having two arithmetic operators in a	row, such as
	       X*-Y.  Such a construct is nonstandard, and can produce unex-
	       pected results in more complicated situations such as X**-Y*Z.
	       g77 along with many other compilers, interprets this example
	       differently than	many programmers, and a	few other compilers.
	       Specifically, g77 interprets X**-Y*Z as (X**(-Y))*Z, while oth-
	       ers might think it should be interpreted	as X**(-(Y*Z)).

	       A revealing example is the constant expression 2**-2*1.,	which
	       g77 evaluates to	.25, while others might	evaluate it to 0., the
	       difference resulting from the way precedence affects type pro-

	       (The -fpedantic option also warns about expressions having two
	       arithmetic operators in a row.)

	   o   Expressions with	a unary	minus followed by an operand and then
	       a binary	operator other than plus or minus.  For	example, -2**2
	       produces	a warning, because the precedence is -(2**2), yielding
	       -4, not (-2)**2,	which yields 4,	and which might	represent what
	       a programmer expects.

	       An example of an	expression producing different results in a
	       surprising way is -I*S, where I holds the value -2147483648 and
	       S holds 0.5.  On	many systems, negating I results in the	same
	       value, not a positive number, because it	is already the lower
	       bound of	what an	"INTEGER(KIND=1)" variable can hold.  So, the
	       expression evaluates to a positive number, while	the
	       ``expected'' interpretation, (-I)*S, would evaluate to a	nega-
	       tive number.

	       Even cases such as -I*J produce warnings, even though, in most
	       configurations and situations, there is no computational	dif-
	       ference between the results of the two interpretations---the
	       purpose of this warning is to warn about	differing interpreta-
	       tions and encourage a better style of coding, not to identify
	       only those places where bugs might exist	in the user's code.

	   o   "DO" loops with "DO" variables that are not of integral
	       type---that is, using "REAL" variables as loop control vari-
	       ables.  Although	such loops can be written to work in the
	       ``obvious'' way,	the way	g77 is required	by the Fortran stan-
	       dard to interpret such code is likely to	be quite different
	       from the	way many programmers expect.  (This is true of all
	       "DO" loops, but the differences are pronounced for non-integral
	       loop control variables.)

	   Make	all warnings into errors.

       -W  Turns on ``extra warnings'' and, if optimization is specified via
	   -O, the -Wuninitialized option.  (This might	change in future ver-
	   sions of g77

	   ``Extra warnings'' are issued for:

	   o   Unused parameters to a procedure	(when -Wunused also is speci-

	   o   Overflows involving floating-point constants (not available for
	       certain configurations).

       Some of these have no effect when compiling programs written in For-

	   These options all could have	some relevant meaning for GNU Fortran
	   programs, but are not yet supported.

       Options for Debugging Your Program or GNU Fortran

       GNU Fortran has various special options that are	used for debugging
       either your program or g77

       -g  Produce debugging information in the	operating system's native for-
	   mat (stabs, COFF, XCOFF, or DWARF).	GDB can	work with this debug-
	   ging	information.

	   A sample debugging session looks like this (note the	use of the

		   $ cat gdb.f
			 DATA A	/1.,2.,3.,4.,5.,6.,7.,8.,9.,10./
			 A(5) =	4.
		   $ g77 -g -O gdb.f
		   $ gdb a.out
		   (gdb) break MAIN__
		   Breakpoint 1	at 0x8048e96: file gdb.f, line 4.
		   (gdb) run
		   Starting program: /home/toon/g77-bugs/./a.out
		   Breakpoint 1, MAIN__	() at gdb.f:4
		   4		 A(5) =	4.
		   Current language:  auto; currently fortran
		   (gdb) print a(5)
		   $1 =	5
		   (gdb) step
		   5		 PRINT*,A
		   (gdb) print a(5)
		   $2 =	4

	   One could also add the setting of the breakpoint and	the first run
	   command to the file .gdbinit	in the current directory, to simplify
	   the debugging session.

       Options That Control Optimization

       Most Fortran users will want to use no optimization when	developing and
       testing programs, and use -O or -O2 when	compiling programs for late-
       cycle testing and for production	use.  However, note that certain diag-
       nostics---such as for uninitialized variables---depend on the flow
       analysis	done by	-O, i.e. you must use -O or -O2	to get such diagnos-

       The following flags have	particular applicability when compiling	For-
       tran programs:

	   (Intel x86 architecture only.)

	   Noticeably improves performance of g77 programs making heavy	use of
	   "REAL(KIND=2)" ("DOUBLE PRECISION") data on some systems.  In par-
	   ticular, systems using Pentium, Pentium Pro,	586, and 686 implemen-
	   tations of the i386 architecture execute programs faster when
	   "REAL(KIND=2)" ("DOUBLE PRECISION") data are	aligned	on 64-bit
	   boundaries in memory.

	   This	option can, at least, make benchmark results more consistent
	   across various system configurations, versions of the program, and
	   data	sets.

	   Note: The warning in	the gcc	documentation about this option	does
	   not apply, generally	speaking, to Fortran code compiled by g77

	   Also	also note: The negative	form of	-malign-double is
	   -mno-align-double, not -benign-double.

	   Might help a	Fortran	program	that depends on	exact IEEE conformance
	   on some machines, but might slow down a program that	doesn't.

	   This	option is effective when the floating-point unit is set	to
	   work	in IEEE	854 `extended precision'---as it typically is on x86
	   and m68k GNU	systems---rather than IEEE 754 double precision.
	   -ffloat-store tries to remove the extra precision by	spilling data
	   from	floating-point registers into memory and this typically
	   involves a big performance hit.  However, it	doesn't	affect inter-
	   mediate results, so that it is only partially effective.  `Excess
	   precision' is avoided in code like:

		   a = b + c
		   d = a * e

	   but not in code like:

			 d = (b	+ c) * e

	   For another,	potentially better, way	of controlling the precision,
	   see @ref{Floating-point precision}.

	   Might improve optimization of loops.

	   Don't compile statement functions inline.  Might reduce the size of
	   a program unit---which might	be at expense of some speed (though it
	   should compile faster).  Note that if you are not optimizing, no
	   functions can be expanded inline.

	   Might allow some programs designed to not be	too dependent on IEEE
	   behavior for	floating-point to run faster, or die trying.  Sets
	   -funsafe-math-optimizations,	and -fno-trapping-math.

	   Allow optimizations that may	be give	incorrect results for certain
	   IEEE	inputs.

	   Allow the compiler to assume	that floating-point arithmetic will
	   not generate	traps on any inputs.  This is useful, for example,
	   when	running	a program using	IEEE "non-stop"	floating-point arith-

	   Might make some loops run faster.

	   Might improve performance on	some code.

	   Typically improves performance on code using	iterative "DO" loops
	   by unrolling	them and is probably generally appropriate for For-
	   tran, though	it is not turned on at any optimization	level.	Note
	   that	outer loop unrolling isn't done	specifically; decisions	about
	   whether to unroll a loop are	made on	the basis of its instruction

	   Also, no `loop discovery'[1]	is done, so only loops written with
	   "DO"	benefit	from loop optimizations, including---but not limited
	   to---unrolling.  Loops written with "IF" and	"GOTO" are not cur-
	   rently recognized as	such.  This option unrolls only	iterative "DO"
	   loops, not "DO WHILE" loops.

	   Probably improves performance on code using "DO WHILE" loops	by
	   unrolling them in addition to iterative "DO"	loops.	In the absence
	   of "DO WHILE", this option is equivalent to -funroll-loops but pos-
	   sibly slower.

	   In general, the optimizations enabled with these options will lead
	   to faster code being	generated by GNU Fortran; hence	they are
	   enabled by default when issuing the g77 command.

	   -fmove-all-movables and -freduce-all-givs will enable loop opti-
	   mization to move all	loop-invariant index computations in nested
	   loops over multi-rank array dummy arguments out of these loops.

	   -frerun-loop-opt will move offset calculations resulting from the
	   fact	that Fortran arrays by default have a lower bound of 1 out of
	   the loops.

	   These three options are intended to be removed someday, once	loop
	   optimization	is sufficiently	advanced to perform all	those trans-
	   formations without help from	these options.

       Options Controlling the Preprocessor

       These options control the C preprocessor, which is run on each C	source
       file before actual compilation.

       Some of these options also affect how g77 processes the "INCLUDE"
       directive.  Since this directive	is processed even when preprocessing
       is not requested, it is not described in	this section.

       However,	the "INCLUDE" directive	does not apply preprocessing to	the
       contents	of the included	file itself.

       Therefore, any file that	contains preprocessor directives (such as
       "#include", "#define", and "#if") must be included via the "#include"
       directive, not via the "INCLUDE"	directive.  Therefore, any file	con-
       taining preprocessor directives,	if included, is	necessarily included
       by a file that itself contains preprocessor directives.

       Options for Directory Search

       These options affect how	the cpp	preprocessor searches for files	speci-
       fied via	the "#include" directive.  Therefore, when compiling Fortran
       programs, they are meaningful when the preprocessor is used.

       Some of these options also affect how g77 searches for files specified
       via the "INCLUDE" directive, although files included by that directive
       are not,	themselves, preprocessed.  These options are:

	   These affect	interpretation of the "INCLUDE"	directive (as well as
	   of the "#include" directive of the cpp preprocessor).

	   Note	that -Idir must	be specified without any spaces	between	-I and
	   the directory name---that is, -Ifoo/bar is valid, but -I foo/bar is
	   rejected by the g77 compiler	(though	the preprocessor supports the
	   latter form).  Also note that the general behavior of -I and
	   "INCLUDE" is	pretty much the	same as	of -I with "#include" in the
	   cpp preprocessor, with regard to looking for	header.gcc files and
	   other such things.

       Options for Code	Generation Conventions

       These machine-independent options control the interface conventions
       used in code generation.

       Most of them have both positive and negative forms; the negative	form
       of -ffoo	would be -fno-foo.  In the table below,	only one of the	forms
       is listed---the one which is not	the default.  You can figure out the
       other form by either removing no- or adding it.

	   Treat each program unit as if the "SAVE" statement was specified
	   for every local variable and	array referenced in it.	 Does not
	   affect common blocks.  (Some	Fortran	compilers provide this option
	   under the name -static.)

	   Specify that	variables and arrays that are local to a program unit
	   (not	in a common block and not passed as an argument) are to	be
	   initialized to binary zeros.

	   Since there is a run-time penalty for initialization	of variables
	   that	are not	given the "SAVE" attribute, it might be	a good idea to
	   also	use -fno-automatic with	-finit-local-zero.

	   Do not generate code	designed to be compatible with code generated
	   by f2c use the GNU calling conventions instead.

	   The f2c calling conventions require functions that return type
	   "REAL(KIND=1)" to actually return the C type	"double", and func-
	   tions that return type "COMPLEX" to return the values via an	extra
	   argument in the calling sequence that points	to where to store the
	   return value.  Under	the GNU	calling	conventions, such functions
	   simply return their results as they would in	GNU C---"REAL(KIND=1)"
	   functions return the	C type "float",	and "COMPLEX" functions	return
	   the GNU C type "complex" (or	its "struct" equivalent).

	   This	does not affect	the generation of code that interfaces with
	   the "libg2c"	library.

	   However, because the	"libg2c" library uses f2c calling conventions,
	   g77 rejects attempts	to pass	intrinsics implemented by routines in
	   this	library	as actual arguments when -fno-f2c is used, to avoid
	   bugs	when they are actually called by code expecting	the GNU	call-
	   ing conventions to work.

	   For example,	INTRINSIC ABS;CALL FOO(ABS) is rejected	when -fno-f2c
	   is in force.	 (Future versions of the g77 run-time library might
	   offer routines that provide GNU-callable versions of	the routines
	   that	implement the f2c intrinsics that may be passed	as actual
	   arguments, so that valid programs need not be rejected when
	   -fno-f2c is used.)

	   Caution: If -fno-f2c	is used	when compiling any source file used in
	   a program, it must be used when compiling all Fortran source	files
	   used	in that	program.

	   Specify that	use of "libg2c"	(or the	original "libf2c") is
	   required.  This is the default for the current version of g77

	   Currently it	is not valid to	specify	-fno-f2c-library.  This	option
	   is provided so users	can specify it in shell	scripts	that build
	   programs and	libraries that require the "libf2c" library, even when
	   being compiled by future versions of	g77 that might otherwise
	   default to generating code for an incompatible library.

	   Do not transform names of entities specified	in the Fortran source
	   file	by appending underscores to them.

	   With	-funderscoring in effect, g77 appends two underscores to names
	   with	underscores and	one underscore to external names with no
	   underscores.	 (g77 also appends two underscores to internal names
	   with	underscores to avoid naming collisions with external names.
	   The -fno-second-underscore option disables appending	of the second
	   underscore in all cases.)

	   This	is done	to ensure compatibility	with code produced by many
	   UNIX	Fortran	compilers, including f2c which perform the same	trans-

	   Use of -fno-underscoring is not recommended unless you are experi-
	   menting with	issues such as integration of (GNU) Fortran into
	   existing system environments	(vis-a-vis existing libraries, tools,
	   and so on).

	   For example,	with -funderscoring, and assuming other	defaults like
	   -fcase-lower	and that j() and max_count() are external functions
	   while my_var	and lvar are local variables, a	statement like

		   I = J() + MAX_COUNT (MY_VAR,	LVAR)

	   is implemented as something akin to:

		   i = j_() + max_count__(&my_var__, &lvar);

	   With	-fno-underscoring, the same statement is implemented as:

		   i = j() + max_count(&my_var,	&lvar);

	   Use of -fno-underscoring allows direct specification	of user-
	   defined names while debugging and when interfacing g77 code with
	   other languages.

	   Note	that just because the names match does not mean	that the
	   interface implemented by g77	for an external	name matches the
	   interface implemented by some other language	for that same name.
	   That	is, getting code produced by g77 to link to code produced by
	   some	other compiler using this or any other method can be only a
	   small part of the overall solution---getting	the code generated by
	   both	compilers to agree on issues other than	naming can require
	   significant effort, and, unlike naming disagreements, linkers nor-
	   mally cannot	detect disagreements in	these other areas.

	   Also, note that with	-fno-underscoring, the lack of appended	under-
	   scores introduces the very real possibility that a user-defined
	   external name will conflict with a name in a	system library,	which
	   could make finding unresolved-reference bugs	quite difficult	in
	   some	cases---they might occur at program run	time, and show up only
	   as buggy behavior at	run time.

	   In future versions of g77 we	hope to	improve	naming and linking
	   issues so that debugging always involves using the names as they
	   appear in the source, even if the names as seen by the linker are
	   mangled to prevent accidental linking between procedures with
	   incompatible	interfaces.

	   Do not append a second underscore to	names of entities specified in
	   the Fortran source file.

	   This	option has no effect if	-fno-underscoring is in	effect.

	   Otherwise, with this	option,	an external name such as MAX_COUNT is
	   implemented as a reference to the link-time external	symbol
	   max_count_, instead of max_count__.

	   Ignore the #ident directive.

	   Treat initial values	of zero	as if they were	any other value.

	   As of version 0.5.18, g77 normally treats "DATA" and	other state-
	   ments that are used to specify initial values of zero for variables
	   and arrays as if no values were actually specified, in the sense
	   that	no diagnostics regarding multiple initializations are pro-

	   This	is done	to speed up compiling of programs that initialize
	   large arrays	to zeros.

	   Use -fzeros to revert to the	simpler, slower	behavior that can
	   catch multiple initializations by keeping track of all initializa-
	   tions, zero or otherwise.

	   Caution: Future versions of g77 might disregard this	option (and
	   its negative	form, the default) or interpret	it somewhat differ-
	   ently.  The interpretation changes will affect only non-standard
	   programs; standard-conforming programs should not be	affected.

	   Implement "COMPLEX" arithmetic via emulation, instead of using the
	   facilities of the gcc back end that provide direct support of "com-
	   plex" arithmetic.

	   (gcc	had some bugs in its back-end support for "complex" arith-
	   metic, due primarily	to the support not being completed as of ver-
	   sion	2.8.1 and "egcs" 1.1.2.)

	   Use -femulate-complex if you	suspect	code-generation	bugs, or expe-
	   rience compiler crashes, that might result from g77 using the "COM-
	   PLEX" support in the	gcc back end.  If using	that option fixes the
	   bugs	or crashes you are seeing, that	indicates a likely g77 bugs
	   (though, all	compiler crashes are considered	bugs), so, please
	   report it.  (Note that the known bugs, now believed fixed, produced
	   compiler crashes rather than	causing	the generation of incorrect

	   Use of this option should not affect	how Fortran code compiled by
	   g77 works in	terms of its interfaces	to other code, e.g. that com-
	   piled by f2c

	   As of GCC version 3.0, this option is not necessary anymore.

	   Caution: Future versions of g77 might ignore	both forms of this

	   Version info: These options are not supported by versions of	g77
	   based on gcc	version	2.8.

	   These options specify to what degree	aliasing (overlap) is permit-
	   ted between arguments (passed as pointers) and "COMMON" (external,
	   or public) storage.

	   The default for Fortran code, as mandated by	the FORTRAN 77 and
	   Fortran 90 standards, is -fargument-noalias-global.	The default
	   for code written in the C language family is	-fargument-alias.

	   Note	that, on some systems, compiling with -fforce-addr in effect
	   can produce more optimal code when the default aliasing options are
	   in effect (and when optimization is enabled).

	   Disable diagnostics about inter-procedural analysis problems, such
	   as disagreements about the type of a	function or a procedure's
	   argument, that might	cause a	compiler crash when attempting to
	   inline a reference to a procedure within a program unit.  (The
	   diagnostics themselves are still produced, but as warnings, unless
	   -Wno-globals	is specified, in which case no relevant	diagnostics
	   are produced.)

	   Further, this option	disables such inlining,	to avoid compiler
	   crashes resulting from incorrect code that would otherwise be diag-

	   As such, this option	might be quite useful when compiling existing,
	   ``working'' code that happens to have a few bugs that do not	gener-
	   ally	show themselves, but which g77 diagnoses.

	   Use of this option therefore	has the	effect of instructing g77 to
	   behave more like it did up through version,	when it	paid
	   little or no	attention to disagreements between program units about
	   a procedure's type and argument information,	and when it performed
	   no inlining of procedures (except statement functions).

	   Without this	option,	g77 defaults to	performing the potentially
	   inlining procedures as it started doing in version 0.5.20, but as
	   of version 0.5.21, it also diagnoses	disagreements that might cause
	   such	inlining to crash the compiler as (fatal) errors, and warns
	   about similar disagreements that are	currently believed to not
	   likely to result in the compiler later crashing or producing	incor-
	   rect	code.

	   Use back end's C-like constructs (pointer plus offset) instead of
	   its "ARRAY_REF" construct to	handle all array references.

	   Note: This option is	not supported.	It is intended for use only by
	   g77 developers, to evaluate code-generation issues.	It might be
	   removed at any time.

	   Enable generation of	run-time checks	for array subscripts and sub-
	   string start	and end	points against the (locally) declared minimum
	   and maximum values.

	   The current implementation uses the "libf2c"	library	routine
	   "s_rnge" to print the diagnostic.

	   However, whereas f2c	generates a single check per reference for a
	   multi-dimensional array, of the computed offset against the valid
	   offset range	(0 through the size of the array), g77 generates a
	   single check	per subscript expression.  This	catches	some cases of
	   potential bugs that f2c does	not, such as references	to below the
	   beginning of	an assumed-size	array.

	   g77 also generates checks for "CHARACTER" substring references,
	   something f2c currently does	not do.

	   Use the new -ffortran-bounds-check option to	specify	bounds-check-
	   ing for only	the Fortran code you are compiling, not	necessarily
	   for code written in other languages.

	   Note: To provide more detailed information on the offending sub-
	   script, g77 provides	the "libg2c" run-time library routine "s_rnge"
	   with	somewhat differently-formatted information.  Here's a sample

		   Subscript out of range on file line 4, procedure rnge.f/bf.
		   Attempt to access the -6-th element of variable b[subscript-2-of-2].

	   The above message indicates that the	offending source line is line
	   4 of	the file rnge.f, within	the program unit (or statement func-
	   tion) named bf.  The	offended array is named	b.  The	offended array
	   dimension is	the second for a two-dimensional array,	and the
	   offending, computed subscript expression was	-6.

	   For a "CHARACTER" substring reference, the second line has this

		   Attempt to access the 11-th element of variable a[start-substring].

	   This	indicates that the offended "CHARACTER"	variable or array is
	   named a, the	offended substring position is the starting (leftmost)
	   position, and the offending substring expression is 11.

	   (Though the verbage of "s_rnge" is not ideal	for the	purpose	of the
	   g77 compiler, the above information should provide adequate diag-
	   nostic abilities to it users.)

       Some of these do	not work when compiling	programs written in Fortran:

	   You should not use these except strictly the	same way as you	used
	   them	to build the version of	"libg2c" with which you	will be	link-
	   ing all code	compiled by g77	with the same option.

	   This	probably either	has no effect on Fortran programs, or makes
	   them	act loopy.

	   Do not use this when	compiling Fortran programs, or there will be

	   This	probably will break any	calls to the "libg2c" library, at the
	   very	least, even if it is built with	the same option.

       GNU Fortran currently does not make use of any environment variables to
       control its operation above and beyond those that affect	the operation
       of gcc.

       For instructions	on reporting bugs, see <>.
       Use of the gccbug script	to report bugs is recommended.

       1.  loop	discovery refers to the	process	by which a compiler, or	indeed
	   any reader of a program, determines which portions of the program
	   are more likely to be executed repeatedly as	it is being run.  Such
	   discovery typically is done early when compiling using optimization
	   techniques, so the ``discovered'' loops get more attention---and
	   more	run-time resources, such as registers---from the compiler.  It
	   is easy to ``discover'' loops that are constructed out of looping
	   constructs in the language (such as Fortran's "DO").	 For some pro-
	   grams, ``discovering'' loops	constructed out	of lower-level con-
	   structs (such as "IF" and "GOTO") can lead to generation of more
	   optimal code	than otherwise.

       gpl(7), gfdl(7),	fsf-funding(7),	cpp(1),	gcov(1), gcc(1), as(1),	ld(1),
       gdb(1), adb(1), dbx(1), sdb(1) and the Info entries for gcc, cpp, g77,
       as, ld, binutils	and gdb.

       See the Info entry for g77 for contributors to GCC and G77.

       Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002 Free Software
       Foundation, Inc.

       Permission is granted to	copy, distribute and/or	modify this document
       under the terms of the GNU Free Documentation License, Version 1.1 or
       any later version published by the Free Software	Foundation; with the
       Invariant Sections being	``GNU General Public License'' and ``Funding
       Free Software'',	the Front-Cover	texts being (a)	(see below), and with
       the Back-Cover Texts being (b) (see below).  A copy of the license is
       included	in the gfdl(7) man page.

       (a) The FSF's Front-Cover Text is:

	    A GNU Manual

       (b) The FSF's Back-Cover	Text is:

	    You	have freedom to	copy and modify	this GNU Manual, like GNU
	    software.  Copies published	by the Free Software Foundation	raise
	    funds for GNU development.

gcc-3.2.2			  2003-02-25				G77(1)


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