g++.1

早期freebsd实现

.\" Copyright (c) 1991 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 "27dec1991" "GNU Tools" "GNU Tools"
.de BP
.sp
.ti \-.2i
\(**
..
.SH NAME
g++ \- GNU project C++ Compiler (v2 preliminary)
.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
\&\|', or `\|\c
.B .cxx\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
.BI +e N
control whether virtual function definitions in classes
are used to generate code, or only to define interfaces for their
callers.  These options are provided for compatibility with cfront
1.x usage; the recommended GNU C++ usage is to use 
.B #pragma interface
and 
.B
#pragma implementation\c
\&, instead.

With `\|\c
.B +e0\c
\&\|', virtual function definitions in classes are declared extern;
the declaration is used only as an interface specification, not to
generate code for the virtual functions (in this compilation).

With `\|\c
.B +e1\c
\&\|', 
.B g++
actually generates the code implementing virtual functions
defined in the code, and makes them publicly visible.
.TP
.B \-fall\-virtual
When you use the `\|\c
.B \-fall\-virtual\c
\&\|', all member functions
(except for constructor functions and new/delete member operators)
declared in the same class with a ``method-call'' operator method are
treated as virtual functions of the given class.  In effect, all
of these methods become ``implicitly virtual.''

This does \c
.I not\c
\& mean that all calls to these methods will be made through the
internal table of virtual functions.  There are some circumstances
under which it is obvious that a call to a given virtual function can
be made directly, and in these cases the calls still go direct.

The effect of making all methods of a class with a declared
\&`\|\c
.B
operator->()()\c
\&\|' implicitly virtual using `\|\c
.B \-fall\-virtual\c
\&\|' extends
also to all non-constructor methods of any class derived from such a
class.
.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 \-fgnu\-binutils
.TP
.B \-fno\-gnu\-binutils
`\|\c
.B \-fgnu\-binutils
\&\|' (the default for most, but not all, platforms) makes GNU C++
emit extra information for static initialization and finalization.
This information has to be passed from the assembler to the GNU
linker.  Some assemblers won't pass this information; you must either
use GNU
.B as
or specify the option `\|\c
.B \-fno\-gnu\-binutils\c
\&\|'.

With `\|\c
.B \-fno\-gnu\-binutils\c
\&\|', you must use the program
.B collect
(part of the GCC distribution) for linking.
.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
If `\|\c
.B \-fdefault\-inline\c
\&\|' is enabled then 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.  By popular
demand, this option is now the default.  To keep GNU C++ from inlining
these member functions, specify `\|\c
.B \-fno\-default\-inline\c
\&\|'.
.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 \-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