invoke.texi

理解和实践操作系统的一本好书

@end table

@node Error and Warning Options
@section Options to request or suppress errors and warnings
@cindex options, warnings
@cindex options, errors
@cindex warnings, suppressing
@cindex messages, error
@cindex messages, warning
@cindex suppressing warnings

Errors are diagnostic messages that report that the GNU Fortran compiler
cannot compile the relevant piece of source code.  The compiler will
continue to process the program in an attempt to report further errors
to aid in debugging, but will not produce any compiled output.  

Warnings are diagnostic messages that report constructions which
are not inherently erroneous but which are risky or suggest there is
likely to be a bug in the program.  Unless @option{-Werror} is specified,
they do not prevent compilation of the program.

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

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

@table @gcctabopt
@item -fmax-errors=@var{n}
@opindex @code{fmax-errors=}@var{n}
@cindex errors, limiting
Limits the maximum number of error messages to @var{n}, at which point
GNU Fortran bails out rather than attempting to continue processing the
source code.  If @var{n} is 0, there is no limit on the number of error
messages produced.

@item -fsyntax-only
@opindex @code{fsyntax-only}
@cindex syntax checking
Check the code for syntax errors, but don't actually compile it.  This
will generate module files for each module present in the code, but no
other output file.

@item -pedantic
@opindex @code{pedantic}
Issue warnings for uses of extensions to Fortran 95.
@option{-pedantic} also applies to C-language constructs where they
occur in GNU Fortran source files, such as use of @samp{\e} in a
character constant within a directive like @code{#include}.

Valid Fortran 95 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 @option{-pedantic} to check programs for conformance.
They soon find that it does not do quite what they want---it finds some
nonstandard practices, but not all.
However, improvements to GNU Fortran in this area are welcome.

This should be used in conjunction with @option{-std=f95} or
@option{-std=f2003}.

@item -pedantic-errors
@opindex @code{pedantic-errors}
Like @option{-pedantic}, except that errors are produced rather than
warnings.

@item -Wall
@opindex @code{Wall}
@cindex all warnings
@cindex warnings, all
Enables commonly used warning options pertaining to usage that
we recommend avoiding and that we believe are easy to avoid.
This currently includes @option{-Waliasing},
@option{-Wampersand}, @option{-Wsurprising}, @option{-Wnonstd-intrinsics},
@option{-Wno-tabs}, and @option{-Wline-truncation}.

@item -Waliasing
@opindex @code{Waliasing}
@cindex aliasing
@cindex warnings, aliasing
Warn about possible aliasing of dummy arguments. Specifically, it warns
if the same actual argument is associated with a dummy argument with
@code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call
with an explicit interface.

The following example will trigger the warning.
@smallexample
  interface
    subroutine bar(a,b)
      integer, intent(in) :: a
      integer, intent(out) :: b
    end subroutine
  end interface
  integer :: a

  call bar(a,a)
@end smallexample

@item -Wampersand
@opindex @code{Wampersand}
@cindex warnings, ampersand
@cindex &
Warn about missing ampersand in continued character constants. The warning is
given with @option{-Wampersand}, @option{-pedantic}, @option{-std=f95}, and
@option{-std=f2003}. Note: With no ampersand given in a continued character
constant, GNU Fortran assumes continuation at the first non-comment,
non-whitespace character after the ampersand that initiated the continuation.

@item -Wcharacter-truncation
@opindex @code{Wcharacter-truncation}
@cindex warnings, character truncation
Warn when a character assignment will truncate the assigned string.

@item -Wconversion
@opindex @code{Wconversion}
@cindex warnings, conversion
@cindex conversion
Warn about implicit conversions between different types.

@item -Wimplicit-interface
@opindex @code{Wimplicit-interface}
@cindex warnings, implicit interface
Warn if a procedure is called without an explicit interface.
Note this only checks that an explicit interface is present.  It does not
check that the declared interfaces are consistent across program units.

@item -Wnonstd-intrinsics
@opindex @code{Wnonstd-intrinsics}
@cindex warnings, non-standard intrinsics
Warn if the user tries to use an intrinsic that does not belong to the 
standard the user has chosen via the @option{-std} option.

@item -Wsurprising
@opindex @code{Wsurprising}
@cindex warnings, suspicious code
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.

@item
A TRANSFER specifies a source that is shorter than the destination.
@end itemize

@item -Wtabs
@opindex @code{Wtabs}
@cindex warnings, tabs
@cindex tabulators
By default, tabs are accepted as whitespace, but tabs are not members
of the Fortran Character Set.  For continuation lines, a tab followed
by a digit between 1 and 9 is supported.  @option{-Wno-tabs} will cause
a warning to be issued if a tab is encountered. Note, @option{-Wno-tabs}
is active for @option{-pedantic}, @option{-std=f95}, @option{-std=f2003},
and @option{-Wall}.

@item -Wunderflow
@opindex @code{Wunderflow}
@cindex warnings, underflow
@cindex underflow
Produce a warning when numerical constant expressions are
encountered, which yield an UNDERFLOW during compilation.

@item -Wunused-parameter
@opindex @code{Wunused-parameter}
@cindex warnings, unused parameter
@cindex unused parameter
Contrary to @command{gcc}'s meaning of @option{-Wunused-parameter},
@command{gfortran}'s implementation of this option does not warn
about unused dummy arguments, but about unused @code{PARAMETER} values.
@option{-Wunused-parameter} is not included in @option{-Wall} but is
implied by @option{-Wall -Wextra}.

@item -Werror
@opindex @code{Werror}
@cindex warnings, to errors
Turns all warnings into errors.
@end table

@xref{Error and Warning Options,,Options to Request or Suppress Errors and
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 the GNU Fortran compiler.

@table @gcctabopt
@item -fdump-parse-tree
@opindex @code{fdump-parse-tree}
Output the internal parse tree before starting code generation.  Only
really useful for debugging the GNU Fortran compiler itself.

@item -ffpe-trap=@var{list}
@opindex @code{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 value).

Some of the routines in the Fortran runtime library, like
@samp{CPU_TIME}, are likely to to trigger floating point exceptions when
@code{ffpe-trap=precision} is used. For this reason, the use of 
@code{ffpe-trap=precision} is not recommended.

@item -fbacktrace
@opindex @code{fbacktrace}
@cindex backtrace
@cindex trace
Specify that, when a runtime error is encountered or a deadly signal is
emitted (segmentation fault, illegal instruction, bus error or
floating-point exception), the Fortran runtime
library should output a backtrace of the error.  This option
only has influence for compilation of the Fortran main program.

@item -fdump-core
@cindex core, dump
@opindex @code{fdump-core}
Request that a core-dump file is written to disk when a runtime error
is encountered on systems that support core dumps. This option is
only effective for the compilation of the Fortran main program.
@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 GNU Fortran 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
@item -I@var{dir}
@opindex @code{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 @file{.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.

@item -M@var{dir}
@item -J@var{dir}
@opindex @code{M}@var{dir}
@opindex @code{J}@var{dir}
@cindex paths, search
@cindex module search path
This option specifies where to put @file{.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.

@item -fintrinsic-modules-path @var{dir}
@opindex @code{fintrinsic-modules-path} @var{dir}
@cindex paths, search
@cindex module search path
This option specifies the location of pre-compiled intrinsic modules, if
they are not in the default location expected by the compiler.
@end table

@node Link Options
@section Influencing the linking step
@cindex options, linking
@cindex linking, static

These options come into play when the compiler links object files into an 
executable output file. They are meaningless if the compiler is not doing 
a link step.

@table @gcctabopt
@item -static-libgfortran
@opindex @code{static-libgfortran}
On systems that provide @file{libgfortran} as a shared and a static
library, this option forces the use of the static version. If no
shared version of @file{libgfortran} was built when the compiler was
configured, this option has no effect.
@end table


@node Runtime Options