invoke.texi

gcc-fortran,linux使用fortran的编译软件。很好用的。

@item -Wnonstd-intrinsic
Warn if the user tries to use an intrinsic that does not belong to the 
standard the user has chosen via the -std option.


@cindex -Wsurprising
@cindex options, -Wsurprising
@item -Wsurprising
@cindex Suspicious
Produce a warning when ``suspicious'' code constructs are encountered.
While technically legal these usually indicate that an error has been made.

This currently produces a warning under the following circumstances:

@itemize @bullet
@item
An INTEGER SELECT construct has a CASE that can never be matched as its
lower value is greater than its upper value.

@item
A LOGICAL SELECT construct has three CASE statements.
@end itemize

@cindex -Wunderflow
@cindex options, -Wunderflow
@item -Wunderflow
@cindex UNDERFLOW
Produce a warning when numerical constant expressions are
encountered, which yield an UNDERFLOW during compilation.


@cindex -Wunused-labels option
@cindex options, -Wunused-labels
@item -Wunused-labels
@cindex unused labels
@cindex labels, unused
Warn whenever a label is defined but never referenced.


@cindex -Werror
@cindex options, -Werror
@item -Werror
Turns all warnings into errors.


@cindex -W option
@cindex options, -W
@item -W
@cindex extra warnings
@cindex warnings, extra
Turns on ``extra warnings'' and, if optimization is specified
via @option{-O}, the @option{-Wuninitialized} option.
(This might change in future versions of @command{gfortran}
@end table

@xref{Warning Options,,Options to Request or Suppress Warnings,
gcc,Using the GNU Compiler Collection (GCC)}, for information on more
options offered by the GBE shared by @command{gfortran}, @command{gcc} and
other GNU compilers.

Some of these have no effect when compiling programs written in Fortran.

@node Debugging Options
@section Options for Debugging Your Program or GNU Fortran
@cindex options, debugging
@cindex debugging information options

GNU Fortran has various special options that are used for debugging
either your program or @command{gfortran}

@table @gcctabopt
@cindex -fdump-parse-tree option
@cindex option, -fdump-parse-tree
@item -fdump-parse-tree
Output the internal parse tree before starting code generation.  Only
really useful for debugging gfortran itself.
@end table

@table @gcctabopt
@cindex -ffpe-trap=@var{list} option
@cindex option, -ffpe-trap=@var{list}
@item -ffpe-trap=@var{list}
Specify a list of IEEE exceptions when a Floating Point Exception
(FPE) should be raised.  On most systems, this will result in a SIGFPE
signal being sent and the program being interrupted, producing a core
file useful for debugging.  @var{list} is a (possibly empty) comma-separated
list of the following IEEE exceptions: @samp{invalid} (invalid floating
point operation, such as @code{sqrt(-1.0)}), @samp{zero} (division by
zero), @samp{overflow} (overflow in a floating point operation),
@samp{underflow} (underflow in a floating point operation),
@samp{precision} (loss of precision during operation) and @samp{denormal}
(operation produced a denormal denormal value).
@end table

@xref{Debugging Options,,Options for Debugging Your Program or GCC,
gcc,Using the GNU Compiler Collection (GCC)}, for more information on
debugging options.

@node Directory Options
@section Options for Directory Search
@cindex directory, options
@cindex options, directory search
@cindex search path

@cindex INCLUDE directive
@cindex directive, INCLUDE
These options affect how @command{gfortran} searches
for files specified by the @code{INCLUDE} directive and where it searches
for previously compiled modules.

It also affects the search paths used by @command{cpp} when used to preprocess
Fortran source.

@table @gcctabopt
@cindex -Idir option
@cindex options, -Idir
@item -I@var{dir}
@cindex directory, search paths for inclusion
@cindex inclusion, directory search paths for
@cindex search paths, for included files
@cindex paths, search
@cindex module search path
These affect interpretation of the @code{INCLUDE} directive
(as well as of the @code{#include} directive of the @command{cpp}
preprocessor).

Also note that the general behavior of @option{-I} and
@code{INCLUDE} is pretty much the same as of @option{-I} with
@code{#include} in the @command{cpp} preprocessor, with regard to
looking for @file{header.gcc} files and other such things.

This path is also used to search for @samp{.mod} files when previously
compiled modules are required by a @code{USE} statement.

@xref{Directory Options,,Options for Directory Search,
gcc,Using the GNU Compiler Collection (GCC)}, for information on the
@option{-I} option.

@cindex -Mdir option
@cindex option, -Mdir
@item -M@var{dir}
@item -J@var{dir}
This option specifies where to put @samp{.mod} files for compiled modules.
It is also added to the list of directories to searched by an @code{USE}
statement.

The default is the current directory.

@option{-J} is an alias for @option{-M} to avoid conflicts with existing
GCC options.
@end table

@node Runtime Options
@section Influencing runtime behavior
@cindex runtime, options

These options affect the runtime behavior of @command{gfortran}.
@table @gcctabopt
@cindex -fconvert=@var{conversion} option
@item -fconvert=@var{conversion}
Specify the representation of data for unformatted files.  Valid
values for conversion are: @samp{native}, the default; @samp{swap},
swap between big- and little-endian; @samp{big-endian}, use big-endian
representation for unformatted files; @samp{little-endian}, use little-endian
representation for unformatted files.

@emph{This option has an effect only when used in the main program.
The @code{CONVERT} specifier and the GFORTRAN_CONVERT_UNIT environment
variable override the default specified by -fconvert.}
@end table

@node Code Gen Options
@section Options for Code Generation Conventions
@cindex code generation, conventions
@cindex options, code generation
@cindex run-time, options

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 @option{-ffoo} would be @option{-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 @option{no-} or adding
it.

@table @gcctabopt
@cindex @option{-fno-automatic} option
@cindex options, @option{-fno-automatic}
@item -fno-automatic
@cindex SAVE statement
@cindex statements, SAVE
Treat each program unit as if the @code{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
@option{-static}.)

@cindex @option{-ff2c} option
@cindex options, @option{-ff2c}
@item -ff2c
@cindex calling convention
@cindex @command{f2c} calling convention
@cindex @command{g77} calling convention
@cindex libf2c calling convention
Generate code designed to be compatible with code generated
by @command{g77} and @command{f2c}.

The calling conventions used by @command{g77} (originally implemented
in @command{f2c}) require functions that return type
default @code{REAL} to actually return the C type @code{double}, and
functions that return type @code{COMPLEX} to return the values via an
extra argument in the calling sequence that points to where to
store the return value.  Under the default GNU calling conventions, such
functions simply return their results as they would in GNU
C -- default @code{REAL} functions return the C type @code{float}, and
@code{COMPLEX} functions return the GNU C type @code{complex}.
Additionally, this option implies the @option{-fsecond-underscore}
option, unless @option{-fno-second-underscore} is explicitly requested.

This does not affect the generation of code that interfaces with
the @command{libgfortran} library.

@emph{Caution:} It is not a good idea to mix Fortran code compiled
with @code{-ff2c} with code compiled with the default @code{-fno-f2c}
calling conventions as, calling @code{COMPLEX} or default @code{REAL}
functions between program parts which were compiled with different
calling conventions will break at execution time.

@emph{Caution:} This will break code which passes intrinsic functions
of type default @code{REAL} or @code{COMPLEX} as actual arguments, as
the library implementations use the @command{-fno-f2c} calling conventions.

@cindex @option{-fno-underscoring option}
@cindex options, @option{-fno-underscoring}
@item -fno-underscoring
@cindex underscore
@cindex symbol names, underscores
@cindex transforming symbol names
@cindex symbol names, transforming
Do not transform names of entities specified in the Fortran
source file by appending underscores to them.

With @option{-funderscoring} in effect, @command{gfortran} appends one
underscore to external names with no underscores.  This is done to ensure
compatibility with code produced by many UNIX Fortran compilers.

@emph{Caution}: The default behavior of @command{gfortran} is
incompatible with @command{f2c} and @command{g77}, please use the
@option{-ff2c} option if you want object files compiled with
@option{gfortran} to be compatible with object code created with these
tools.

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

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

@smallexample
I = J() + MAX_COUNT (MY_VAR, LVAR)
@end smallexample

@noindent
is implemented as something akin to:

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

With @option{-fno-underscoring}, the same statement is implemented as:

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

Use of @option{-fno-underscoring} allows direct specification of
user-defined names while debugging and when interfacing @command{gfortran}
code with other languages.

Note that just because the names match does @emph{not} mean that the
interface implemented by @command{gfortran} for an external name matches the
interface implemented by some other language for that same name.
That is, getting code produced by @command{gfortran} 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 normally
cannot detect disagreements in these other areas.

Also, note that with @option{-fno-underscoring}, the lack of appended
underscores 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 @command{gfortran} 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.

@cindex @option{-fsecond-underscore option}
@cindex options, @option{-fsecond-underscore}
@item -fsecond-underscore
@cindex underscore
@cindex symbol names, underscores
@cindex transforming symbol names
@cindex symbol names, transforming
@cindex @command{f2c} calling convention
@cindex @command{g77} calling convention
@cindex libf2c calling convention
By default, @command{gfortran} appends an underscore to external
names.  If this option is used @command{gfortran} appends two
underscores to names with underscores and one underscore to external names
with no underscores.  (@command{gfortran} also appends two underscores to
internal names with underscores to avoid naming collisions with external
names.

This option has no effect if @option{-fno-underscoring} is
in effect.  It is implied by the @option{-ff2c} option.

Otherwise, with this option, an external name such as @samp{MAX_COUNT}
is implemented as a reference to the link-time external symbol
@samp{max_count__}, instead of @samp{max_count_}.  This is required
for compatibility with @command{g77} and @command{f2c}, and is implied
by use of the @option{-ff2c} option.


@cindex -fbounds-check option
@cindex -ffortran-bounds-check option
@item -fbounds-check
@cindex bounds checking
@cindex range checking
@cindex array bounds checking
@cindex subscript checking
@cindex checking subscripts
Enable generation of run-time checks for array subscripts
and against the declared minimum and maximum values.  It also
checks array indices for assumed and deferred
shape arrays against the actual allocated bounds.

In the future this may also include other forms of checking, eg. checking
substring references.


@cindex -fmax-stack-var-size option
@item -fmax-stack-var-size=@var{n}
This option specifies the size in bytes of the largest array that will be put
on the stack.

This option currently only affects local arrays declared with constant
bounds, and may not apply to all character variables.
Future versions of @command{gfortran} may improve this behavior.

The default value for @var{n} is 32768.

@cindex -fpackderived
@item -fpackderived
@cindex Structure packing
This option tells gfortran to pack derived type members as closely as
possible.  Code compiled with this option is likely to be incompatible
with code compiled without this option, and may execute slower.

@cindex -frepack-arrays option
@item -frepack-arrays
@cindex Repacking arrays
In some circumstances @command{gfortran} may pass assumed shape array
sections via a descriptor describing a discontiguous area of memory.
This option adds code to the function prologue to repack the data into
a contiguous block at runtime.

This should result in faster accesses to the array.  However it can introduce
significant overhead to the function call, especially  when the passed data
is discontiguous.

@cindex -fshort-enums
@item -fshort-enums
This option is provided for interoperability with C code that was
compiled with the @command{-fshort-enums} option.  It will make
@command{gfortran} choose the smallest @code{INTEGER} kind a given
enumerator set will fit in, and give all its enumerators this kind.
@end table

@xref{Code Gen Options,,Options for Code Generation Conventions,
gcc,Using the GNU Compiler Collection (GCC)}, for information on more options
offered by the GBE
shared by @command{gfortran} @command{gcc} and other GNU compilers.


@c man end

@node Environment Variables
@section Environment Variables Affecting GNU Fortran
@cindex environment variables

@c man begin ENVIRONMENT

GNU Fortran 95 currently does not make use of any environment
variables to control its operation above and beyond those
that affect the operation of @command{gcc}.

@xref{Environment Variables,,Environment Variables Affecting GCC,
gcc,Using the GNU Compiler Collection (GCC)}, for information on environment
variables.

@xref{Runtime}, for environment variables that affect the
run-time behavior of @command{gfortran} programs.
@c man end