G++(1) GNU Tools G++(1) NAME g++ - GNU project C++ Compiler (v2 preliminary) SYNOPSIS g++ [_o_p_t_i_o_n | _f_i_l_e_n_a_m_e ]... DESCRIPTION The C and C++ compilers are integrated. Both process input files through one or more of four stages: preprocessing, compilation, assembly, and linking. This man page contains full descriptions for _o_n_l_y C++ specific aspects of the com- piler, 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', or `.cxx'. OPTIONS There are many command-line options, including options to control details of optimization, warnings, and code genera- tion, which are common to both gcc and g++. For full infor- mation 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: -f_n_a_m_e and -fno-_n_a_m_e (or -W_n_a_m_e and -Wno-_n_a_m_e). 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. -D_m_a_c_r_o Define macro _m_a_c_r_o with the string `1' as its defini- tion. -D_m_a_c_r_o=_d_e_f_n Define macro _m_a_c_r_o as _d_e_f_n. -E Stop after the preprocessing stage; do not run the com- piler proper. The output is preprocessed source code, which is sent to the standard output. +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 com- patibility with cfront 1.x usage; the recommended GNU C++ usage is to use #pragma interface and #pragma GNU Tools Last change: 27dec1991 1 G++(1) GNU Tools G++(1) implementation, instead. With `+e0', 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 `+e1', g++ actually generates the code implement- ing virtual functions defined in the code, and makes them publicly visible. -fall-virtual When you use the `-fall-virtual', 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 _n_o_t mean that all calls to these methods will be made through the internal table of virtual func- tions. 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 `operator->()()' implicitly virtual using `-fall-virtual' extends also to all non-constructor methods of any class derived from such a class. -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++ initial- izes `y' directly from the call to foo () without going GNU Tools Last change: 27dec1991 2 G++(1) GNU Tools G++(1) 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. -fgnu-binutils -fno-gnu-binutils `-fgnu-binutils ' (the default for most, but not all, platforms) makes GNU C++ emit extra information for static initialization and finalization. This informa- tion has to be passed from the assembler to the GNU linker. Some assemblers won't pass this information; you must either use GNU as or specify the option `-fno-gnu-binutils'. With `-fno-gnu-binutils', you must use the program col- lect (part of the GCC distribution) for linking. -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 func- tion 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. GNU Tools Last change: 27dec1991 3 G++(1) GNU Tools G++(1) 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 com- piler 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 func- tion has exactly the same access privileges as every other, and the cache need not be flushed. -fno-default-inline If `-fdefault-inline' is enabled then 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. By popular demand, this option is now the default. To keep GNU C++ from inlin- ing these member functions, specify `-fno-default-inline'. -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 say- ing 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 unneces- sary for many programs. You can use `-fnonnull-objects' to omit the checks for null, if your program doesn't require the default checking. -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 GNU Tools Last change: 27dec1991 4 G++(1) GNU Tools G++(1) class member function. However, for backwards compati- bility, 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 debug- ging 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 vari- ables you declared may not exist at all; flow of con- trol 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 out- put. This makes it reasonable to use the optimizer for programs that might have bugs. -I_d_i_r Append directory _d_i_r to the list of directories searched for include files. -L_d_i_r Add directory _d_i_r to the list of directories to be searched for `-l'. -l_l_i_b_r_a_r_y Use the library named _l_i_b_r_a_r_y when linking. (C++ pro- grams often require `-lg++' for successful linking.) -O Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. Without `-O', the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you would expect from the source code. Without `-O', only variables declared register are allocated in registers. The resulting compiled code is a little worse than produced by PCC without `-O'. GNU Tools Last change: 27dec1991 5 G++(1) GNU Tools G++(1) With `-O', the compiler tries to reduce code size and execution time. -o _f_i_l_e Place output in file _f_i_l_e. -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. -static On systems that support dynamic linking, this prevents linking with the shared libraries. (`-g' also has this effect.) On other systems, this option has no effect. -traditional Attempt to support some aspects of traditional C com- pilers. Specifically, for both C and C++ programs: o+ In the preprocessor, comments convert to nothing at all, rather than to a space. This allows traditional token concatenation. o+ 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. o+ 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 test- ing both of these predefined macros you can distinguish four situations: GNU C, traditional GNU C, other ANSI C compilers, and other old C compilers. o+ In the preprocessor, comments convert to nothing at all, rather than to a space. This allows traditional token concatenation. o+ 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. GNU Tools Last change: 27dec1991 6 G++(1) GNU Tools G++(1) o+ 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 test- ing both of these predefined macros you can distinguish four situations: GNU C, traditional GNU C, other ANSI C compilers, and other old C compilers. o+ String ``constants'' are not necessarily constant; they are stored in writable space, and identical looking constants are allocated separately. (This is the same as the effect of `-fwritable-strings'.) 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'. -U_m_a_c_r_o Undefine macro _m_a_c_r_o. -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 func- tions must match the type signature of a virtual func- tion declared in the base class. Use this option to request warnings when a derived class declares a func- tion that may be an erroneous attempt to define a vir- tual 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. -w Inhibit all warning messages. PRAGMAS Two `#pragma' directives are supported for GNU C++, to per- mit using the same header file for two purposes: as a defin- ition 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 GNU Tools Last change: 27dec1991 7 G++(1) GNU Tools G++(1) 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 "_o_b_j_e_c_t_s.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 _T_M_P_D_I_R/cc* temporary files _L_I_B_D_I_R/cpp preprocessor _L_I_B_D_I_R/cc1plus compiler _L_I_B_D_I_R/collect linker front end needed on some machines _L_I_B_D_I_R/libgcc.a GCC subroutine library /lib/crt[01n].o start-up routine _L_I_B_D_I_R/ccrt0 additional start-up routine for C++ GNU Tools Last change: 27dec1991 8 G++(1) GNU Tools G++(1) /lib/libc.a standard C library, see _i_n_t_r_o(3) /usr/include standard directory for #include files _L_I_B_D_I_R/include standard gcc directory for #include files _L_I_B_D_I_R/g++-include additional g++ directory for #include _L_I_B_D_I_R is usually /usr/local/lib/_m_a_c_h_i_n_e/_v_e_r_s_i_o_n. _T_M_P_D_I_R 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. _U_s_i_n_g _a_n_d _P_o_r_t_i_n_g _G_N_U _C_C (_f_o_r _v_e_r_s_i_o_n _2._0), Richard M. Stallman, November 1990; _T_h_e _C _P_r_e_p_r_o_c_e_s_s_o_r, Richard M. Stallman, July 1990; _U_s_i_n_g _G_D_B: _A _G_u_i_d_e _t_o _t_h_e _G_N_U _S_o_u_r_c_e- _L_e_v_e_l _D_e_b_u_g_g_e_r, Richard M. Stallman and Roland H. Pesch, December 1991; _U_s_i_n_g _a_s: _t_h_e _G_N_U _A_s_s_e_m_b_l_e_r, Dean Elsner, Jay Fenlason & friends, March 1991; _g_l_d: _t_h_e _G_N_U _l_i_n_k_e_r, Steve Chamberlain and Roland Pesch, April 1991. BUGS Report bugs to bug-gcc@prep.ai.mit.edu. Bugs tend actually to be fixed if they can be isolated, so it is in your interest to report them in such a way that they can be easily reproduced. COPYING Copyright (c) 1991 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this per- mission notice are preserved on all copies. Permission is granted to copy and distribute modified ver- sions of this manual under the conditions for verbatim copy- ing, provided that the entire resulting derived work is dis- tributed 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 condi- tions 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 Last change: 27dec1991 9