path: root/gcc/cp/g++.1

.\" Copyright (c) 1991, 1992 Free Software Foundation              -*-Text-*-
.\" See section COPYING for conditions for redistribution
.\" FIXME: no info here on predefines.  Should there be?  extra for C++...
.TH G++ 1 "30apr1993" "GNU Tools" "GNU Tools"
.de BP
.sp
.ti \-.2i
\(**
..
.SH NAME
g++ \- GNU project C++ Compiler
.SH SYNOPSIS
.RB g++ " [" \c
.IR option " | " filename " ].\|.\|.
.SH DESCRIPTION
The C and C++ compilers are integrated;
.B g++
is a script to call
.B gcc with options to recognize C++.  
.B gcc
processes input files
through one or more of four stages: preprocessing, compilation,
assembly, and linking.  This man page contains full descriptions for 
.I 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
.BR gcc ( 1 ).

C++ source files use one of the suffixes `\|\c
.B .C\c
\&\|', `\|\c
.B .cc\c
\&\|', `\|\c
.B .cxx\c
\&\|', `\|\c
.B .cpp\c
\&\|', or `\|\c
.B .c++\c
\&\|'; preprocessed C++ files use the suffix `\|\c
.B .ii\c
\&\|'.
.SH OPTIONS
There are many command-line options, including options to control
details of optimization, warnings, and code generation, which are
common to both 
.B gcc
and
.B g++\c
\&.  For full information on all options, see 
.BR gcc ( 1 ).

Options must be separate: `\|\c
.B \-dr\c
\&\|' is quite different from `\|\c
.B \-d \-r
\&\|'. 

Most `\|\c
.B \-f\c
\&\|' and `\|\c
.B \-W\c
\&\|' options have two contrary forms: 
.BI \-f name
and
.BI \-fno\- name\c
\& (or 
.BI \-W name
and
.BI \-Wno\- name\c
\&). Only the non-default forms are shown here.

.TP
.B \-c
Compile or assemble the source files, but do not link.  The compiler
output is an object file corresponding to each source file.
.TP
.BI \-D macro
Define macro \c
.I macro\c
\& with the string `\|\c
.B 1\c
\&\|' as its definition.
.TP
.BI \-D macro = defn
Define macro \c
.I macro\c
\& as \c
.I defn\c
\&.
.TP
.B \-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.
.TP
.B \-fall\-virtual
Treat all possible member functions as virtual, implicitly.  All
member functions (except for constructor functions and
.B new
or
.B 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.
.TP
.B \-fdollars\-in\-identifiers
Permit the use of `\|\c
.B $\c
\&\|' in identifiers.
Traditional C allowed the character `\|\c
.B $\c
\&\|' to form part of identifiers; by default, GNU C also
allows this.  However, ANSI C forbids `\|\c
.B $\c
\&\|' 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).
.TP
.B \-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:
.sp
.br
A\ foo\ ();
.br
A\ x\ (foo\ ());\ \ \ //\ x\ initialized\ by\ `foo\ ()',\ no\ ctor\ called
.br
A\ y\ =\ foo\ ();\ \ \ //\ call\ to\ `foo\ ()'\ heads\ to\ temporary,
.br
\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ //\ y\ is\ initialized\ from\ the\ temporary.
.br
.sp
Note the difference!  With this flag, GNU C++ initializes `\|\c
.B y\c
\&\|' directly
from the call to 
.B foo ()
without going through a temporary.
.TP
.B \-fenum\-int\-equiv
Normally GNU C++ allows conversion of 
.B enum
to
.B int\c
\&, but not the other way around.  Use this option if you want GNU C++
to allow conversion of
.B int
to 
.B enum
as well.  
.TP
.B \-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 `\|\c
.B #pragma implementation\c
\&\|' (the definition) or
`\|\c
.B #pragma interface\c
\&\|' (declarations).

When your code is compiled with `\|\c
.B \-fexternal\-templates\c
\&\|', all
template instantiations are external.  You must arrange for all
necessary instantiations to appear in the implementation file; you can
do this with a \c
.B typedef\c
\& that references each instantiation needed.
Conversely, when you compile using the default option
`\|\c
.B \-fno\-external\-templates\c
\&\|', all template instantiations are
explicitly internal.
.TP
.B \-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
.B collect2
program to make sure the system linker includes
constructors and destructors.  (\c
.B collect2
is included in the GNU CC distribution.)  For systems which
.I must
use
.B collect2\c
\&, the compiler driver
.B gcc
is configured to do this automatically.
.TP
.B \-fmemoize\-lookups
.TP
.B \-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
.sp
.br
\ \ cout\ <<\ "This\ "\ <<\ p\ <<\ "\ has\ "\ <<\ n\ <<\ "\ legs.\en";
.br
.sp
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.  `\|\c
.B \-fmemoize\-lookups\c
\&\|' enables
the software cache.

Because access privileges (visibility) to members and member functions
may differ from one function context to the next, 
.B g++
may need to flush the cache. With the `\|\c
.B \-fmemoize\-lookups\c
\&\|' flag, the cache is flushed after every
function that is compiled.  The `\|\c
\-fsave\-memoized\c
\&\|' 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.
.TP
.B \-fno\-default\-inline
Do not make member functions inline by default merely because they are
defined inside the class scope.  Otherwise, when you specify
.B \-O\c
\&, member functions defined inside class scope are compiled
inline by default; i.e., you don't need to add `\|\c
.B inline\c
\&\|' in front of
the member function name.
.TP
.B \-fno\-strict\-prototype
Consider the declaration \c
.B int foo ();\c
\&.  In C++, this means that the
function \c
.B foo\c
\& takes no arguments.  In ANSI C, this is declared
.B int foo(void);\c
\&.  With the flag `\|\c
.B \-fno\-strict\-prototype\c
\&\|',
declaring functions with no arguments is equivalent to declaring its
argument list to be untyped, i.e., \c
.B int foo ();\c
\& is equivalent to
saying \c
.B int foo (...);\c
\&.
.TP
.B \-fnonnull\-objects
Normally, GNU C++ makes conservative assumptions about objects reached
through references.  For example, the compiler must check that `\|\c
.B a\c
\&\|' is not null in code like the following:
.br
\ \ \ \ obj\ &a\ =\ g\ ();
.br
\ \ \ \ a.f\ (2);
.br
Checking that references of this sort have non-null values requires
extra code, however, and it is unnecessary for many programs.  You can
use `\|\c
.B \-fnonnull\-objects\c
\&\|' to omit the checks for null, if your program doesn't require the
default checking.
.TP
.B \-fhandle\-signatures
.TP
.B \-fno\-handle\-signatures
These options control the recognition of the \c
.B signature\c
\& and \c
.B sigof\c
\& constructs for specifying abstract types.  By default, these
constructs are not recognized.
.TP
.B \-fthis\-is\-variable
The incorporation of user-defined free store management into C++ has
made assignment to \c
.B this\c
\& an anachronism.  Therefore, by default GNU
C++ treats the type of \c
.B this\c
\& in a member function of \c
.B class X\c
\&
to be \c
.B X *const\c
\&.  In other words, it is illegal to assign to
\c
.B this\c
\& within a class member function.  However, for backwards
compatibility, you can invoke the old behavior by using
\&`\|\c
.B \-fthis\-is\-variable\c
\&\|'.
.TP
.B \-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, `\|\c
.B \-g\c
\&\|' enables use
of extra debugging information that only GDB can use.

Unlike most other C compilers, GNU CC allows you to use `\|\c
.B \-g\c
\&\|' with
`\|\c
.B \-O\c
\&\|'.  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.
.TP
.BI "\-I" "dir"\c
\&
Append directory \c
.I dir\c
\& to the list of directories searched for include files.
.TP
.BI "\-L" "dir"\c
\&
Add directory \c
.I dir\c
\& to the list of directories to be searched
for `\|\c
.B \-l\c
\&\|'.
.TP
.BI \-l library\c
\&
Use the library named \c
.I library\c
\& when linking.  (C++ programs often require `\|\c
\-lg++\c
\&\|' for successful linking.)
.TP
.B \-nostdinc
Do not search the standard system directories for header files.  Only
the directories you have specified with
.B \-I
options (and the current directory, if appropriate) are searched.
.TP
.B \-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++.)
.TP
.B \-O
Optimize.  Optimizing compilation takes somewhat more time, and a lot
more memory for a large function.
.TP
.BI "\-o " file\c
\&
Place output in file \c
.I file\c
\&.
.TP
.B \-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.
.TP
.B \-traditional
Attempt to support some aspects of traditional C compilers.

Specifically, for both C and C++ programs:
.TP
\ \ \ \(bu
In the preprocessor, comments convert to nothing at all, rather than
to a space.  This allows traditional token concatenation.
.TP
\ \ \ \(bu
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.
.TP
\ \ \ \(bu
The preprocessor does not predefine the macro \c
.B __STDC__\c
\& when you use
`\|\c
.B \-traditional\c
\&\|', but still predefines\c
.B __GNUC__\c
\& (since the GNU extensions indicated by 
.B __GNUC__\c
\& are not affected by
`\|\c
.B \-traditional\c
\&\|').  If you need to write header files that work
differently depending on whether `\|\c
.B \-traditional\c
\&\|' 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.
.PP
.TP
\ \ \ \(bu
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), `\|\c
.B \-traditional\c
\&\|' has one additional effect: assignment to 
.B this
is permitted.  This is the same as the effect of `\|\c
.B \-fthis\-is\-variable\c
\&\|'.
.TP
.BI \-U macro
Undefine macro \c
.I macro\c
\&.
.TP
.B \-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. 
.TP
.B \-Wenum\-clash
Warn when converting between different enumeration types.
.TP
.B \-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.
.TP
.B \-Wtemplate\-debugging
When using templates in a C++ program, warn if debugging is not yet
fully available.
.TP
.B \-w
Inhibit all warning messages.
.TP
.BI +e N
Control how virtual function definitions are used, in a fashion
compatible with
.B cfront
1.x.
.PP

.SH PRAGMAS
Two `\|\c
.B #pragma\c
\&\|' 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.
.TP
.B #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 `\|\c
.B #pragma interface\c
\&\|' is included in a compilation, this auxiliary information
will not be generated (unless the main input source file itself uses
`\|\c
.B #pragma implementation\c
\&\|').  Instead, the object files will contain references to be
resolved at link time.  
.tr !"
.TP
.B #pragma implementation
.TP
.BI "#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 `\|\c
.B #pragma interface\c
\&\|'.  
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 `\|\c
.B #pragma implementation\c
\&\|' with no argument, it applies to an include file with the same
basename as your source file; for example, in `\|\c
.B allclass.cc\c
\&\|', `\|\c
.B #pragma implementation\c
\&\|' by itself is equivalent to `\|\c
.B 
#pragma implementation "allclass.h"\c
\&\|'.  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. 
.SH FILES
.ta \w'LIBDIR/g++\-include 'u
file.h	C header (preprocessor) file
.br
file.i	preprocessed C source file
.br
file.C	C++ source file
.br
file.cc	C++ source file
.br
file.cxx	C++ source file
.br
file.s	assembly language file
.br
file.o	object file
.br
a.out	link edited output
.br
\fITMPDIR\fR/cc\(**	temporary files
.br
\fILIBDIR\fR/cpp	preprocessor
.br
\fILIBDIR\fR/cc1plus	compiler
.br
\fILIBDIR\fR/collect	linker front end needed on some machines
.br
\fILIBDIR\fR/libgcc.a	GCC subroutine library
.br
/lib/crt[01n].o	start-up routine
.br
\fILIBDIR\fR/ccrt0	additional start-up routine for C++
.br
/lib/libc.a	standard C library, see
.IR intro (3)
.br
/usr/include	standard directory for 
.B #include
files
.br
\fILIBDIR\fR/include	standard gcc directory for
.B #include
files
.br
\fILIBDIR\fR/g++\-include	additional g++ directory for
.B #include
.sp
.I LIBDIR
is usually
.B /usr/local/lib/\c
.IR machine / version .
.br
.I TMPDIR
comes from the environment variable 
.B TMPDIR
(default
.B /usr/tmp
if available, else
.B /tmp\c
\&).
.SH "SEE ALSO"
gcc(1), cpp(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1).
.br
.RB "`\|" gcc "\|', `\|" cpp \|', 
.RB `\| as \|', `\| ld \|',
and 
.RB `\| gdb \|'
entries in
.B info\c
\&.
.br
.I 
Using and Porting GNU CC (for version 2.0)\c
, Richard M. Stallman; 
.I
The C Preprocessor\c
, Richard M. Stallman;
.I 
Debugging with GDB: the GNU Source-Level Debugger\c
, Richard M. Stallman and Roland H. Pesch;
.I
Using as: the GNU Assembler\c
, Dean Elsner, Jay Fenlason & friends;
.I
gld: the GNU linker\c
, Steve Chamberlain and Roland Pesch.

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

.SH COPYING
Copyright (c) 1991, 1992, 1993 Free Software Foundation, Inc.
.PP
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.
.PP
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.
.PP
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.
.SH AUTHORS
See the GNU CC Manual for the contributors to GNU CC.