gfortran.texi

理解和实践操作系统的一本好书

@command{-Wl,--whole-archive -lpthread -Wl,--no-whole-archive} is added
to the command line. However, this is not supported by @command{gcc} and
thus not recommended.
@end itemize

@node Argument list functions
@subsection Argument list functions @code{%VAL}, @code{%REF} and @code{%LOC}
@cindex argument list functions
@cindex @code{%VAL}
@cindex @code{%REF}
@cindex @code{%LOC}

GNU Fortran supports argument list functions @code{%VAL}, @code{%REF} 
and @code{%LOC} statements, for backward compatibility with g77. 
It is recommended that these should be used only for code that is 
accessing facilities outside of GNU Fortran, such as operating system 
or windowing facilities. It is best to constrain such uses to isolated 
portions of a program--portions that deal specifically and exclusively 
with low-level, system-dependent facilities. Such portions might well 
provide a portable interface for use by the program as a whole, but are 
themselves not portable, and should be thoroughly tested each time they 
are rebuilt using a new compiler or version of a compiler.

@code{%VAL} passes a scalar argument by value, @code{%REF} passes it by 
reference and @code{%LOC} passes its memory location.  Since gfortran 
already passes scalar arguments by reference, @code{%REF} is in effect 
a do-nothing.  @code{%LOC} has the same effect as a fortran pointer.

An example of passing an argument by value to a C subroutine foo.:
@smallexample
C
C prototype      void foo_ (float x);
C
      external foo
      real*4 x
      x = 3.14159
      call foo (%VAL (x))
      end
@end smallexample

For details refer to the g77 manual
@uref{http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top}.

Also, the gfortran testsuite c_by_val.f and its partner c_by_val.c are
worth a look.



@node Extensions not implemented in GNU Fortran
@section Extensions not implemented in GNU Fortran
@cindex extensions, not implemented

The long history of the Fortran language, its wide use and broad
userbase, the large number of different compiler vendors and the lack of
some features crucial to users in the first standards have lead to the
existence of an important number of extensions to the language. While
some of the most useful or popular extensions are supported by the GNU
Fortran compiler, not all existing extensions are supported. This section
aims at listing these extensions and offering advice on how best make
code that uses them running with the GNU Fortran compiler.

@c More can be found here:
@c   -- http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Missing-Features.html
@c   -- the list of fortran and libgfortran bugs closed as WONTFIX:
@c      http://tinyurl.com/2u4h5y

@menu
* STRUCTURE and RECORD::
@c * UNION and MAP::
* ENCODE and DECODE statements::
@c * Expressions in FORMAT statements::
@c * Q edit descriptor::
@c * AUTOMATIC statement::
@c * TYPE and ACCEPT I/O Statements::
@c * .XOR. operator::
@c * CARRIAGECONTROL, DEFAULTFILE, DISPOSE and RECORDTYPE I/O specifiers::
@c * Omitted arguments in procedure call:
@end menu


@node STRUCTURE and RECORD
@subsection @code{STRUCTURE} and @code{RECORD}
@cindex @code{STRUCTURE}
@cindex @code{RECORD}

Structures are user-defined aggregate data types; this functionality was
standardized in Fortran 90 with an different syntax, under the name of
``derived types''. Here is an example of code using the non portable
structure syntax:

@example
! Declaring a structure named ``item'' and containing three fields:
! an integer ID, an description string and a floating-point price.
STRUCTURE /item/
  INTEGER id
  CHARACTER(LEN=200) description
  REAL price
END STRUCTURE

! Define two variables, an single record of type ``item''
! named ``pear'', and an array of items named ``store_catalog''
RECORD /item/ pear, store_catalog(100)

! We can directly access the fields of both variables
pear.id = 92316
pear.description = "juicy D'Anjou pear"
pear.price = 0.15
store_catalog(7).id = 7831
store_catalog(7).description = "milk bottle"
store_catalog(7).price = 1.2

! We can also manipulates the whole structure
store_catalog(12) = pear
print *, store_catalog(12)
@end example

@noindent
This code can easily be rewritten in the Fortran 90 syntax as following:

@example
! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
! ``TYPE name ... END TYPE''
TYPE item
  INTEGER id
  CHARACTER(LEN=200) description
  REAL price
END TYPE

! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
TYPE(item) pear, store_catalog(100)

! Instead of using a dot (.) to access fields of a record, the
! standard syntax uses a percent sign (%)
pear%id = 92316
pear%description = "juicy D'Anjou pear"
pear%price = 0.15
store_catalog(7)%id = 7831
store_catalog(7)%description = "milk bottle"
store_catalog(7)%price = 1.2

! Assignments of a whole variable don't change
store_catalog(12) = pear
print *, store_catalog(12)
@end example


@c @node UNION and MAP
@c @subsection @code{UNION} and @code{MAP}
@c @cindex @code{UNION}
@c @cindex @code{MAP}
@c
@c For help writing this one, see
@c http://www.eng.umd.edu/~nsw/ench250/fortran1.htm#UNION and
@c http://www.tacc.utexas.edu/services/userguides/pgi/pgiws_ug/pgi32u06.htm


@node ENCODE and DECODE statements
@subsection @code{ENCODE} and @code{DECODE} statements
@cindex @code{ENCODE}
@cindex @code{DECODE}

GNU Fortran doesn't support the @code{ENCODE} and @code{DECODE}
statements.  These statements are best replaced by @code{READ} and
@code{WRITE} statements involving internal files (@code{CHARACTER}
variables and arrays), which have been part of the Fortran standard since
Fortran 77. For example, replace a code fragment like

@smallexample
      INTEGER*1 LINE(80)
      REAL A, B, C
c     ... Code that sets LINE
      DECODE (80, 9000, LINE) A, B, C
 9000 FORMAT (1X, 3(F10.5))
@end smallexample

@noindent
with the following:

@smallexample
      CHARACTER(LEN=80) LINE
      REAL A, B, C
c     ... Code that sets LINE
      READ (UNIT=LINE, FMT=9000) A, B, C
 9000 FORMAT (1X, 3(F10.5))
@end smallexample

Similarly, replace a code fragment like

@smallexample
      INTEGER*1 LINE(80)
      REAL A, B, C
c     ... Code that sets A, B and C
      ENCODE (80, 9000, LINE) A, B, C
 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
@end smallexample

@noindent
with the following:

@smallexample
      INTEGER*1 LINE(80)
      REAL A, B, C
c     ... Code that sets A, B and C
      WRITE (UNIT=LINE, FMT=9000) A, B, C
 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))
@end smallexample


@c ---------------------------------------------------------------------
@c Intrinsic Procedures
@c ---------------------------------------------------------------------

@include intrinsic.texi


@tex
\blankpart
@end tex

@c ---------------------------------------------------------------------
@c Contributing
@c ---------------------------------------------------------------------

@node Contributing
@unnumbered Contributing
@cindex Contributing

Free software is only possible if people contribute to efforts
to create it.
We're always in need of more people helping out with ideas
and comments, writing documentation and contributing code.

If you want to contribute to GNU Fortran,
have a look at the long lists of projects you can take on.
Some of these projects are small,
some of them are large;
some are completely orthogonal to the rest of what is
happening on GNU Fortran,
but others are ``mainstream'' projects in need of enthusiastic hackers.
All of these projects are important!
We'll eventually get around to the things here,
but they are also things doable by someone who is willing and able.

@menu
* Contributors::
* Projects::
* Proposed Extensions::
@end menu


@node Contributors
@section Contributors to GNU Fortran
@cindex Contributors
@cindex Credits
@cindex Authors

Most of the parser was hand-crafted by @emph{Andy Vaught}, who is
also the initiator of the whole project.  Thanks Andy!
Most of the interface with GCC was written by @emph{Paul Brook}.

The following individuals have contributed code and/or
ideas and significant help to the GNU Fortran project
(in alphabetical order):

@itemize @minus
@item Janne Blomqvist
@item Steven Bosscher
@item Paul Brook
@item Tobias Burnus
@item Fran@,{c}ois-Xavier Coudert
@item Bud Davis
@item Jerry DeLisle
@item Erik Edelmann
@item Bernhard Fischer
@item Daniel Franke
@item Richard Guenther
@item Richard Henderson
@item Katherine Holcomb
@item Jakub Jelinek
@item Niels Kristian Bech Jensen
@item Steven Johnson
@item Steven G. Kargl
@item Thomas Koenig
@item Asher Langton
@item H. J. Lu
@item Toon Moene
@item Brooks Moses
@item Andrew Pinski
@item Tim Prince
@item Christopher D. Rickett
@item Richard Sandiford
@item Tobias Schl@"uter
@item Roger Sayle
@item Paul Thomas
@item Andy Vaught
@item Feng Wang
@item Janus Weil
@end itemize

The following people have contributed bug reports,
smaller or larger patches,
and much needed feedback and encouragement for the
GNU Fortran project: 

@itemize @minus
@item Bill Clodius
@item Dominique d'Humi@`eres
@item Kate Hedstrom
@item Erik Schnetter
@end itemize

Many other individuals have helped debug,
test and improve the GNU Fortran compiler over the past few years,
and we welcome you to do the same!
If you already have done so,
and you would like to see your name listed in the
list above, please contact us.


@node Projects
@section Projects

@table @emph

@item Help build the test suite
Solicit more code for donation to the test suite: the more extensive the
testsuite, the smaller the risk of breaking things in the future! We can
keep code private on request.

@item Bug hunting/squishing
Find bugs and write more test cases! Test cases are especially very
welcome, because it allows us to concentrate on fixing bugs instead of
isolating them. Going through the bugzilla database at
@url{http://gcc.gnu.org/bugzilla/} to reduce testcases posted there and
add more information (for example, for which version does the testcase
work, for which versions does it fail?) is also very helpful.

@end table


@node Proposed Extensions
@section Proposed Extensions

Here's a list of proposed extensions for the GNU Fortran compiler, in no particular
order.  Most of these are necessary to be fully compatible with
existing Fortran compilers, but they are not part of the official
J3 Fortran 95 standard.

@subsection Compiler extensions: 
@itemize @bullet
@item
User-specified alignment rules for structures.

@item
Flag to generate @code{Makefile} info.

@item
Automatically extend single precision constants to double.

@item
Compile code that conserves memory by dynamically allocating common and
module storage either on stack or heap.

@item
Compile flag to generate code for array conforma