g++295

G++(1)                             GNU Tools                            G++(1)



NAME
       g++ - GNU project C++ Compiler

SYNOPSIS
       g++ [option | filename ]...

DESCRIPTION
       The C and C++ compilers are integrated; g++ is a script to call gcc
       with options to recognize C++.  gcc processes input files through one
       or more of four stages: preprocessing, compilation, assembly, and
       linking.  This man page contains full descriptions for only C++
       specific aspects of the compiler, though it also contains summaries of
       some general-purpose options.  For a fuller explanation of the
       compiler, see gcc(1).

       C++ source files use one of the suffixes `.C', `.cc', `.cxx', `.cpp',
       or `.c++'; preprocessed C++ files use the suffix `.ii'.

OPTIONS
       There are many command-line options, including options to control
       details of optimization, warnings, and code generation, which are
       common to both gcc and g++.  For full information on all options, see
       gcc(1).

       Options must be separate: `-dr' is quite different from `-d -r '.

       Most `-f' and `-W' options have two contrary forms: -fname and
       -fno-name (or -Wname and -Wno-name). Only the non-default forms are
       shown here.


       -c     Compile or assemble the source files, but do not link.  The
              compiler output is an object file corresponding to each source
              file.

       -Dmacro
              Define macro macro with the string `1' as its definition.

       -Dmacro=defn
              Define macro macro as defn.

       -E     Stop after the preprocessing stage; do not run the compiler
              proper.  The output is preprocessed source code, which is sent
              to the standard output.

       -fall-virtual
              Treat all possible member functions as virtual, implicitly.  All
              member functions (except for constructor functions and new or
              delete member operators) are treated as virtual functions of the
              class where they appear.

              This does not mean that all calls to these member functions will
              be made through the internal table of virtual functions.  Under
              some circumstances, the compiler can determine that a call to a
              given virtual function can be made directly; in these cases the
              calls are direct in any case.

       -fdollars-in-identifiers
              Permit the use of `$' in identifiers.  Traditional C allowed the
              character `$' to form part of identifiers; by default, GNU C
              also allows this.  However, ANSI C forbids `$' in identifiers,
              and GNU C++ also forbids it by default on most platforms (though
              on some platforms it's enabled by default for GNU C++ as well).

       -felide-constructors
              Use this option to instruct the compiler to be smarter about
              when it can elide constructors.  Without this flag, GNU C++ and
              cfront both generate effectively the same code for:

              A foo ();
              A x (foo ());   // x initialized by `foo ()', no ctor called
              A y = foo ();   // call to `foo ()' heads to temporary,
                              // y is initialized from the temporary.

              Note the difference!  With this flag, GNU C++ initializes `y'
              directly from the call to foo () without going through a
              temporary.

       -fenum-int-equiv
              Normally GNU C++ allows conversion of enum to int, but not the
              other way around.  Use this option if you want GNU C++ to allow
              conversion of int to enum as well.

       -fexternal-templates
              Produce smaller code for template declarations, by generating
              only a single copy of each template function where it is
              defined.  To use this option successfully, you must also mark
              all files that use templates with either `#pragma
              implementation' (the definition) or `#pragma interface'
              (declarations).

              When your code is compiled with `-fexternal-templates', all
              template instantiations are external.  You must arrange for all
              necessary instantiations to appear in the implementation file;
              you can do this with a typedef that references each
              instantiation needed.  Conversely, when you compile using the
              default option `-fno-external-templates', all template
              instantiations are explicitly internal.

       -fno-gnu-linker
              Do not output global initializations (such as C++ constructors
              and destructors) in the form used by the GNU linker (on systems
              where the GNU linker is the standard method of handling them).
              Use this option when you want to use a non-GNU linker, which
              also requires using the collect2 program to make sure the system
              linker includes constructors and destructors.  (collect2 is
              included in the GNU CC distribution.)  For systems which must
              use collect2, the compiler driver gcc is configured to do this
              automatically.

       -fmemoize-lookups

       -fsave-memoized
              These flags are used to get the compiler to compile programs
              faster using heuristics.  They are not on by default since they
              are only effective about half the time.  The other half of the
              time programs compile more slowly (and take more memory).

              The first time the compiler must build a call to a member
              function (or reference to a data member), it must (1) determine
              whether the class implements member functions of that name; (2)
              resolve which member function to call (which involves figuring
              out what sorts of type conversions need to be made); and (3)
              check the visibility of the member function to the caller.  All
              of this adds up to slower compilation.  Normally, the second
              time a call is made to that member function (or reference to
              that data member), it must go through the same lengthy process
              again.  This means that code like this

                cout << "This " << p << " has " << n << " legs.\n";

              makes six passes through all three steps.  By using a software
              cache, a ``hit'' significantly reduces this cost.
              Unfortunately, using the cache introduces another layer of
              mechanisms which must be implemented, and so incurs its own
              overhead.  `-fmemoize-lookups' enables the software cache.

              Because access privileges (visibility) to members and member
              functions may differ from one function context to the next, g++
              may need to flush the cache. With the `-fmemoize-lookups' flag,
              the cache is flushed after every function that is compiled.  The
              `-fsave-memoized' flag enables the same software cache, but when
              the compiler determines that the context of the last function
              compiled would yield the same access privileges of the next
              function to compile, it preserves the cache.  This is most
              helpful when defining many member functions for the same class:
              with the exception of member functions which are friends of
              other classes, each member function has exactly the same access
              privileges as every other, and the cache need not be flushed.

       -fno-default-inline
              Do not make member functions inline by default merely because
              they are defined inside the class scope.  Otherwise, when you
              specify -O, member functions defined inside class scope are
              compiled inline by default; i.e., you don't need to add `inline'
              in front of the member function name.

       -fno-strict-prototype
              Consider the declaration int foo ();.  In C++, this means that
              the function foo takes no arguments.  In ANSI C, this is
              declared int foo(void);.  With the flag `-fno-strict-prototype',
              declaring functions with no arguments is equivalent to declaring
              its argument list to be untyped, i.e., int foo (); is equivalent
              to saying int foo (...);.

       -fnonnull-objects
              Normally, GNU C++ makes conservative assumptions about objects
              reached through references.  For example, the compiler must
              check that `a' is not null in code like the following:
                  obj &a = g ();
                  a.f (2);
              Checking that references of this sort have non-null values
              requires extra code, however, and it is unnecessary for many
              programs.  You can use `-fnonnull-objects' to omit the checks
              for null, if your program doesn't require the default checking.

       -fhandle-signatures

       -fno-handle-signatures
              These options control the recognition of the signature and sigof
              constructs for specifying abstract types.  By default, these
              constructs are not recognized.

       -fthis-is-variable
              The incorporation of user-defined free store management into C++
              has made assignment to this an anachronism.  Therefore, by
              default GNU C++ treats the type of this in a member function of
              class X to be X *const.  In other words, it is illegal to assign
              to this within a class member function.  However, for backwards
              compatibility, you can invoke the old behavior by using
              `-fthis-is-variable'.

       -g     Produce debugging information in the operating system's native
              format (for DBX or SDB or DWARF).  GDB also can work with this
              debugging information.  On most systems that use DBX format,
              `-g' enables use of extra debugging information that only GDB
              can use.

              Unlike most other C compilers, GNU CC allows you to use `-g'
              with `-O'.  The shortcuts taken by optimized code may
              occasionally produce surprising results: some variables you
              declared may not exist at all; flow of control may briefly move
              where you did not expect it; some statements may not be executed
              because they compute constant results or their values were
              already at hand; some statements may execute in different places
              because they were moved out of loops.

              Nevertheless it proves possible to debug optimized output.  This
              makes it reasonable to use the optimizer for programs that might
              have bugs.

       -Idir   Append directory dir to the list of directories searched for
              include files.

       -Ldir   Add directory dir to the list of directories to be searched for
              `-l'.

       -llibrary
               Use the library named library when linking.  (C++ programs
              often require `-lg++' for successful linking.)

       -nostdinc
              Do not search the standard system directories for header files.
              Only the directories you have specified with -I options (and the
              current directory, if appropriate) are searched.

       -nostdinc++
              Do not search for header files in the standard directories
              specific to C++, but do still search the other standard
              directories.  (This option is used when building libg++.)

       -O     Optimize.  Optimizing compilation takes somewhat more time, and
              a lot more memory for a large function.

       -o file
               Place output in file file.

       -S     Stop after the stage of compilation proper; do not assemble.
              The output is an assembler code file for each non-assembler
              input file specified.

       -traditional
              Attempt to support some aspects of traditional C compilers.

              Specifically, for both C and C++ programs:

          ·   In the preprocessor, comments convert to nothing at all, rather
              than to a space.  This allows traditional token concatenation.

          ·   In the preprocessor, macro arguments are recognized within
              string constants in a macro definition (and their values are
              stringified, though without additional quote marks, when they
              appear in such a context).  The preprocessor always considers a
              string constant to end at a newline.

          ·   The preprocessor does not predefine the macro __STDC__ when you
              use `-traditional', but still predefines__GNUC__ (since the GNU
              extensions indicated by __GNUC__ are not affected by
              `-traditional').  If you need to write header files that work
              differently depending on whether `-traditional' is in use, by
              testing both of these predefined macros you can distinguish four
              situations: GNU C, traditional GNU C, other ANSI C compilers,
              and other old C compilers.

          ·   String ``constants'' are not necessarily constant; they are
              stored in writable space, and identical looking constants are
              allocated separately.

              For C++ programs only (not C), `-traditional' has one additional
              effect: assignment to this is permitted.  This is the same as
              the effect of `-fthis-is-variable'.

       -Umacro
              Undefine macro macro.

       -Wall  Issue warnings for conditions which pertain to usage that we
              recommend avoiding and that we believe is easy to avoid, even in
              conjunction with macros.

       -Wenum-clash
              Warn when converting between different enumeration types.

       -Woverloaded-virtual
              In a derived class, the definitions of virtual functions must
              match the type signature of a virtual function declared in the
              base class.  Use this option to request warnings when a derived
              class declares a function that may be an erroneous attempt to
              define a virtual function: that is, warn when a function with
              the same name as a virtual function in the base class, but with
              a type signature that doesn't match any virtual functions from
              the base class.

       -Wtemplate-debugging
              When using templates in a C++ program, warn if debugging is not
              yet fully available.

       -w     Inhibit all warning messages.

       +eN    Control how virtual function definitions are used, in a fashion
              compatible with cfront 1.x.

PRAGMAS
       Two `#pragma' directives are supported for GNU C++, to permit using the
       same header file for two purposes: as a definition of interfaces to a
       given object class, and as the full definition of the contents of that
       object class.

       #pragma interface
              Use this directive in header files that define object classes,
              to save space in most of the object files that use those
              classes.  Normally, local copies of certain information (backup
              copies of inline member functions, debugging information, and
              the internal tables that implement virtual functions) must be
              kept in each object file that includes class definitions.  You
              can use this pragma to avoid such duplication.  When a header
              file containing `#pragma interface' is included in a
              compilation, this auxiliary information will not be generated
              (unless the main input source file itself uses `#pragma
              implementation').  Instead, the object files will contain
              references to be resolved at link time.

       #pragma implementation

       #pragma implementation "objects.h"
              Use this pragma in a main input file, when you want full output
              from included header files to be generated (and made globally
              visible).  The included header file, in turn, should use
              `#pragma interface'.  Backup copies of inline member functions,
              debugging information, and the internal tables used to implement
              virtual functions are all generated in implementation files.

              If you use `#pragma implementation' with no argument, it applies
              to an include file with the same basename as your source file;
              for example, in `allclass.cc', `#pragma implementation' by
              itself is equivalent to `#pragma implementation "allclass.h"'.
              Use the string argument if you want a single implementation file
              to include code from multiple header files.

              There is no way to split up the contents of a single header file
              into multiple implementation files.

FILES
       file.h             C header (preprocessor) file
       file.i             preprocessed C source file
       file.C             C++ source file
       file.cc            C++ source file
       file.cxx           C++ source file
       file.s             assembly language file
       file.o             object file
       a.out              link edited output
       TMPDIR/cc∗         temporary files
       LIBDIR/cpp         preprocessor
       LIBDIR/cc1plus     compiler
       LIBDIR/collect     linker front end needed on some machines
       LIBDIR/libgcc.a    GCC subroutine library
       /lib/crt[01n].o    start-up routine
       LIBDIR/ccrt0       additional start-up routine for C++
       /lib/libc.a        standard C library, see intro(3)
       /usr/include       standard directory for #include files
       LIBDIR/include     standard gcc directory for #include files
       LIBDIR/g++-include additional g++ directory for #include

       LIBDIR is usually /usr/local/lib/machine/version.
       TMPDIR comes from the environment variable TMPDIR (default /usr/tmp if
       available, else /tmp).

SEE ALSO
       gcc(1), cpp(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1).
       `gcc', `cpp', `as',`ld', and `gdb' entries in info.
       Using and Porting GNU CC (for version 2.0), Richard M. Stallman; The C
       Preprocessor, Richard M. Stallman; Debugging with GDB: the GNU Source-
       Level Debugger, Richard M. Stallman and Roland H. Pesch; Using as: the
       GNU Assembler, Dean Elsner, Jay Fenlason & friends; gld: the GNU
       linker, Steve Chamberlain and Roland Pesch.


BUGS
       For instructions on how to report bugs, see the GCC manual.


COPYING
       Copyright (c) 1991, 1992, 1993 Free Software Foundation, Inc.

       Permission is granted to make and distribute verbatim copies of this
       manual provided the copyright notice and this permission notice are
       preserved on all copies.

       Permission is granted to copy and distribute modified versions of this
       manual under the conditions for verbatim copying, provided that the
       entire resulting derived work is distributed under the terms of a
       permission notice identical to this one.

       Permission is granted to copy and distribute translations of this
       manual into another language, under the above conditions for modified
       versions, except that this permission notice may be included in
       translations approved by the Free Software Foundation instead of in the
       original English.

AUTHORS
       See the GNU CC Manual for the contributors to GNU CC.



GNU Tools                          30apr1993                            G++(1)