Celestin Apprentice 2/Apprentice-Release2.iso/Information/Languages/C++/C++ FAQ 4⁄4

Text File | 1994-12-08 | 28.6 KB | 746 lines | [TEXT/R*ch]

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From: [e-mail] (Marshall Cline)
Newsgroups: comp.lang.c++
Subject: C++ FAQ: posting #4/4
Followup-To: comp.lang.c++
Date: 14 Nov 1994 00:26:49 GMT
Organization: Paradigm Shift, Inc (training/consulting/OOD/OOP/C++)
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Summary: Please read this before posting to comp.lang.c++

comp.lang.c++ Frequently Asked Questions list (with answers, fortunately).
Copyright (C) 1991-94 Marshall P. Cline, Ph.D.
Posting 4 of 4.
Posting #1 explains copying permissions, (no)warranty, table-of-contents, etc

==============================================================================
SECTION 17: Linkage-to/relationship-with C
==============================================================================

Q98: How can I call a C function "f(int,char,float)" from C++ code?

Tell the C++ compiler that it is a C function:
    extern "C" void f(int,char,float);

Be sure to include the full function prototype.  A block of many C functions
can be grouped via braces, as in:

    extern "C" {
      void* malloc(size_t);
      char* strcpy(char* dest, const char* src);
      int   printf(const char* fmt, ...);
    }

==============================================================================

Q99: How can I create a C++ function "f(int,char,float)" that is callable by
   my C code?

The C++ compiler must know that "f(int,char,float)" is to be called by a C
compiler using the same "extern C" construct detailed in the previous FAQ.
Then you define the function in your C++ module:

    void f(int x, char y, float z)
    {
      //...
    }

The "extern C" line tells the compiler that the external information sent to
the linker should use C calling conventions and name mangling (e.g., preceded
by a single underscore).  Since name overloading isn't supported by C, you
can't make several overloaded fns simultaneously callable by a C program.

Caveats and implementation dependencies:
 * your "main()" should be compiled with your C++ compiler (for static init).
 * your C++ compiler should direct the linking process (for special libraries).
 * your C and C++ compilers may need to from same vendor (calling convention).

==============================================================================

Q100: Why's the linker giving errors for C/C++ fns being called from C++/C
   fns?

See the previous two FAQs on how to use "extern "C"."

==============================================================================

Q101: How can I pass an object of a C++ class to/from a C function?

Here's an example:

    /****** C/C++ header file: Fred.h ******/
    #ifdef __cplusplus    /*"__cplusplus" is #defined if/only-if compiler is C++*/
      extern "C" {
    #endif

    #ifdef __STDC__
      extern void c_fn(struct Fred*);    /* ANSI-C prototypes */
      extern struct Fred* cplusplus_callback_fn(struct Fred*);
    #else
      extern void c_fn();            /* K&R style */
      extern struct Fred* cplusplus_callback_fn();
    #endif

    #ifdef __cplusplus
      }
    #endif

    #ifdef __cplusplus
      class Fred {
      public:
        Fred();
        void wilma(int);
      private:
        int a_;
      };
    #endif

"Fred.C" would be a C++ module:

    #include "Fred.h"
    Fred::Fred() : a_(0) { }
    void Fred::wilma(int a) : a_(a) { }

    Fred* cplusplus_callback_fn(Fred* fred)
    {
      fred->wilma(123);
      return fred;
    }

"main.C" would be a C++ module:

    #include "Fred.h"

    int main()
    {
      Fred fred;
      c_fn(&fred);
      return 0;
    }

"c-fn.c" would be a C module:

    #include "Fred.h"
    void c_fn(struct Fred* fred)
    {
      cplusplus_callback_fn(fred);
    }

Passing ptrs to C++ objects to/from C fns will FAIL if you pass and get back
something that isn't EXACTLY the same pointer.  For example, DON'T pass a base
class ptr and receive back a derived class ptr, since your C compiler won't
understand the pointer conversions necessary to handle multiple and/or virtual
inheritance.

==============================================================================

Q102: Can my C function access data in an object of a C++ class?

Sometimes.

(First read the previous FAQ on passing C++ objects to/from C functions.)

You can safely access a C++ object's data from a C function if the C++ class:
 * has no virtual functions (including inherited virtual fns)
 * has all its data in the same access-level section (private/protected/public)
 * has no fully-contained subobjects with virtual fns

If the C++ class has any base classes at all (or if any fully contained
subobjects have base classes), accessing the data will TECHNICALLY be
non-portable, since class layout under inheritance isn't imposed by the
language.  However in practice, all C++ compilers do it the same way: the base
class object appears first (in left-to-right order in the event of multiple
inheritance), and subobjects follow.

Furthermore, if the class (or any base class) contains any virtual functions,
you can often (but less than always) assume a "void*" appears in the object
either at the location of the first virtual function or as the first word in
the object.  Again, this is not required by the language, but it is the way
"everyone" does it.

If the class has any virtual base classes, it is even more complicated and less
portable.  One common implementation technique is for objects to contain an
object of the virtual base class (V) last (regardless of where "V" shows up as
a virtual base class in the inheritance hierarchy).  The rest of the object's
parts appear in the normal order.  Every derived class that has V as a virtual
base class actually has a POINTER to the V part of the final object.

==============================================================================

Q103: Why do I feel like I'm "further from the machine" in C++ as opposed to
   C?

Because you are.

As an OOPL, C++ allows you to model the problem domain itself, which allows you
to program in the language of the problem domain rather than in the language of
the solution domain.

One of C's great strengths is the fact that it has "no hidden mechanism": what
you see is what you get.  You can read a C program and "see" every clock cycle.
This is not the case in C++; old line C programmers (such as many of us once
were) are often ambivalent (can anyone say, "hostile") about this feature, but
they soon realize that it provides a level of abstraction and economy of
expression which lowers maintenance costs without destroying run-time
performance.

Naturally you can write bad code in any language; C++ doesn't guarantee any
particular level of quality, reusability, abstraction, or any other measure of
"goodness."  C++ doesn't try to make it impossible for bad programmers to write
bad programs; it enables reasonable developers to create superior software.

==============================================================================
SECTION 18: Pointers to member functions
==============================================================================

Q104: Is the type of "ptr-to-member-fn" different from "ptr-to-fn"?

Yep.

Consider the following function:

    int f(char a, float b);

If this is an ordinary function, its type is:    int (*)      (char,float);
If this is a method of class Fred, its type is:  int (Fred::*)(char,float);

==============================================================================

Q105: How can I ensure objects of my class are always created via "new" rather
   than as locals or global/static objects?

Make sure the class's constructors are "private:", and define "friend" or
"static" fns that return a ptr to the objects created via "new" (make the
constructors "protected:" if you want to allow derived classes).

    class Fred {    //only want to allow dynamicly allocated Fred's
    public:
      static Fred* create()                 { return new Fred();     }
      static Fred* create(int i)            { return new Fred(i);    }
      static Fred* create(const Fred& fred) { return new Fred(fred); }
    private:
      Fred();
      Fred(int i);
      Fred(const Fred& fred);
      virtual ~Fred();
    };

    main()
    {
      Fred* p = Fred::create(5);
      ...
      delete p;
    }

==============================================================================

Q106: How do I pass a ptr to member fn to a signal handler, X event callback,
   etc?

Don't.

Because a member function is meaningless without an object to invoke it on, you
can't do this directly (if The X Windows System was rewritten in C++, it would
probably pass references to OBJECTS around, not just pointers to fns; naturally
the objects would embody the required function and probably a whole lot more).

As a patch for existing software, use a top-level (non-member) function as a
wrapper which takes an object obtained through some other technique (held in a
global, perhaps).  The top-level function would apply the desired member
function against the global object.

E.g., suppose you want to call Fred::memfn() on interrupt:

    class Fred {
    public:
      void memfn();
      static void staticmemfn();    //a static member fn can handle it
      //...
    };

    //wrapper fn remembers the object on which to invoke memfn in a global:
    Fred* object_which_will_handle_signal;
    void Fred_memfn_wrapper() { object_which_will_handle_signal->memfn(); }

    main()
    {
      /* signal(SIGINT, Fred::memfn); */   //Can NOT do this
      signal(SIGINT, Fred_memfn_wrapper);  //Ok
      signal(SIGINT, Fred::staticmemfn);   //Also Ok
    }

Note: static member functions do not require an actual object to be invoked, so
ptrs-to-static-member-fns are type compatible with regular ptrs-to-fns (see ARM
p.25, 158).

==============================================================================

Q107: Why am I having trouble taking the address of a C++ function?

This is a corollary to the previous FAQ.

Long answer: In C++, member fns have an implicit parameter which points to the
object (the "this" ptr inside the member fn).  Normal C fns can be thought of
as having a different calling convention from member fns, so the types of their
ptrs (ptr-to-member-fn vs ptr-to-fn) are different and incompatible.  C++
introduces a new type of ptr, called a ptr-to-member, which can only be invoked
by providing an object (see ARM 5.5).

NOTE: do NOT attempt to "cast" a ptr-to-mem-fn into a ptr-to-fn; the result is
undefined and probably disastrous.  E.g., a ptr-to- member-fn is NOT required
to contain the machine addr of the appropriate fn (see ARM, 8.1.2c, p.158).  As
was said in the last example, if you have a ptr to a regular C fn, use either a
top-level (non-member) fn, or a "static" (class) member fn.

==============================================================================

Q108: How do I declare an array of pointers to member functions?

Keep your sanity with "typedef".

    class Fred {
    public:
      int f(char x, float y);
      int g(char x, float y);
      int h(char x, float y);
      int i(char x, float y);
      //...
    };

    typedef  int (Fred::*FredPtr)(char x, float y);

Here's the array of pointers to member functions:

    FredPtr a[4] = { &Fred::f, &Fred::g, &Fred::h, &Fred::i };

To call one of the member functions on object "fred":

    void userCode(Fred& fred, int methodNum, char x, float y)
    {
      //assume "methodNum" is between 0 and 3 inclusive
      (fred.*a[methodNum])(x, y);
    }

You can make the call somewhat clearer using a #define:

    #define  callMethod(object,ptrToMethod)   ((object).*(ptrToMethod))
    callMethod(fred, a[methodNum]) (x, y);

==============================================================================
SECTION 19: Container classes and templates
==============================================================================

Q109: How can I insert/access/change elements from a linked
   list/hashtable/etc?

I'll use an "inserting into a linked list" as a prototypical example.  It's easy
to allow insertion at the head and tail of the list, but limiting ourselves to
these would produce a library that is too weak (a weak library is almost worse
than no library).

This answer will be a lot to swallow for novice C++'ers, so I'll give a couple
of options.  The first option is easiest; the second and third are better.

[1] Empower the "List" with a "current location," and methods such as
advance(), backup(), atEnd(), atBegin(), getCurrElem(), setCurrElem(Elem),
insertElem(Elem), and removeElem().  Although this works in small examples, the
notion of "a" current position makes it difficult to access elements at two or
more positions within the List (e.g., "for all pairs x,y do the following...").

[2] Remove the above methods from the List itself, and move them to a separate
class, "ListPosition."  ListPosition would act as a "current position" within a
List.  This allows multiple positions within the same List.  ListPosition would
be a friend of List, so List can hide its innards from the outside world (else
the innards of List would have to be publicized via public methods in List).
Note: ListPosition can use operator overloading for things like advance() and
backup(), since operator overloading is syntactic sugar for normal methods.

[3] Consider the entire iteration as an atomic event, and create a class
template to embodies this event.  This enhances performance by allowing the
public access methods (which may be virtual fns) to be avoided during the inner
loop.  Unfortunately you get extra object code in the application, since
templates gain speed by duplicating code.  For more, see [Koenig, "Templates as
interfaces," JOOP, 4, 5 (Sept 91)], and [Stroustrup, "The C++ Programming
Language Second Edition," under "Comparator"].

==============================================================================

Q110: What's the idea behind "templates"?

A template is a cookie-cutter that specifies how to cut cookies that all look
pretty much the same (although the cookies can be made of various kinds of
dough, they'll all have the same basic shape).  In the same way, a class
template is a cookie cutter to description of how to build a family of classes
that all look basically the same, and a function template describes how to
build a family of similar looking functions.

Class templates are often used to build type safe containers (although this
only scratches the surface for how they can be used).

==============================================================================

Q111: What's the syntax / semantics for a "function template"?

Consider this function that swaps its two integer arguments:

    void swap(int& x, int& y)
    {
      int tmp = x;
      x = y;
      y = tmp;
    }

If we also had to swap floats, longs, Strings, Sets, and FileSystems, we'd get
pretty tired of coding lines that look almost identical except for the type.
Mindless repetition is an ideal job for a computer, hence a function template:

    template<class T>
    void swap(T& x, T& y)
    {
      T tmp = x;
      x = y;
      y = tmp;
    }

Every time we used "swap()" with a given pair of types, the compiler will go to
the above definition and will create yet another "template function" as an
instantiation of the above.  E.g.,

    main()
    {
      int    i,j;  /*...*/  swap(i,j);  //instantiates a swap for "int"
      float  a,b;  /*...*/  swap(a,b);  //instantiates a swap for "float"
      char   c,d;  /*...*/  swap(c,d);  //instantiates a swap for "char"
      String s,t;  /*...*/  swap(s,t);  //instantiates a swap for "String"
    }

(note: a "template function" is the instantiation of a "function template").

==============================================================================

Q112: What's the syntax / semantics for a "class template"?

Consider a container class of that acts like an array of integers:

    //this would go into a header file such as "Array.h"
    class Array {
    public:
      Array(int len=10)                  : len_(len), data_(new int[len]){}
     ~Array()                            { delete [] data_; }
      int len() const                    { return len_;     }
      const int& operator[](int i) const { data_[check(i)]; }
            int& operator[](int i)       { data_[check(i)]; }
      Array(const Array&);
      Array& operator= (const Array&);
    private:
      int  len_;
      int* data_;
      int  check(int i) const
        { if (i < 0 || i >= len_) throw BoundsViol("Array", i, len_);
          return i; }
    };

Just as with "swap()" above, repeating the above over and over for Array of
float, of char, of String, of Array-of-String, etc, will become tedious.

    //this would go into a header file such as "Array.h"
    template<class T>
    class Array {
    public:
      Array(int len=10)                : len_(len), data_(new T[len]) { }
     ~Array()                          { delete [] data_; }
      int len() const                  { return len_;     }
      const T& operator[](int i) const { data_[check(i)]; }
            T& operator[](int i)       { data_[check(i)]; }
      Array(const Array<T>&);
      Array& operator= (const Array<T>&);
    private:
      int len_;
      T*  data_;
      int check(int i) const
        { if (i < 0 || i >= len_) throw BoundsViol("Array", i, len_);
          return i; }
    };

Unlike template functions, template classes (instantiations of class templates)
need to be explicit about the parameters over which they are instantiating:

    main()
    {
      Array<int>           ai;
      Array<float>         af;
      Array<char*>         ac;
      Array<String>        as;
      Array< Array<int> >  aai;
    }              // ^^^-- note the space; do NOT use "Array<Array<int>>"
                   //       (the compiler sees ">>" as a single token).

==============================================================================

Q113: What is a "parameterized type"?

Another way to say, "class templates."

A parameterized type is a type that is parameterized over another type or some
value.  List<int> is a type ("List") parameterized over another type ("int").

==============================================================================

Q114: What is "genericity"?

Yet another way to say, "class templates."

Not to be confused with "generality" (which just means avoiding solutions which
are overly specific), "genericity" means class templates.

==============================================================================
SECTION 20: Nuances of particular implementations
==============================================================================

Q115: GNU C++ (g++) produces big executables for tiny programs; Why?

libg++ (the library used by g++) was probably compiled with debug info (-g).
On some machines, recompiling libg++ without debugging can save lots of disk
space (~1 Meg; the down-side: you'll be unable to trace into libg++ calls).
Merely "strip"ping the executable doesn't reclaim as much as recompiling
without -g followed by subsequent "strip"ping the resultant "a.out"s.

Use "size a.out" to see how big the program code and data segments really are,
rather than "ls -s a.out" which includes the symbol table.

==============================================================================

Q116: Is there a yacc-able C++ grammar?

Jim Roskind is the author of a yacc grammar for C++. It's roughly compatible
with the portion of the language implemented by USL cfront 2.0 (no templates,
no exceptions, no run-time-type-identification).  Jim's grammar deviates from
C++ in a couple of minor-but-subtle ways.

The grammar can be accessed by anonymous ftp from the following sites:
 * ics.uci.edu (128.195.1.1) in "gnu/c++grammar2.0.tar.Z".
 * mach1.npac.syr.edu (128.230.7.14) in "pub/C++/c++grammar2.0.tar.Z".

==============================================================================

Q117: What is C++ 1.2?  2.0?  2.1?  3.0?

These are not versions of the language, but rather versions of cfront, which
was the original C++ translator implemented by AT&T.  It has become generally
accepted to use these version numbers as if they were versions of the language
itself.

*VERY* roughly speaking, these are the major features:
 * 2.0 includes multiple/virtual inheritance and pure virtual functions.
 * 2.1 includes semi-nested classes and "delete [] ptr_to_array."
 * 3.0 includes fully-nested classes, templates and "i++" vs "++i."
 * 4.0 will include exceptions.

==============================================================================
SECTION 21: Miscellaneous technical and environmental issues
==============================================================================
SUBSECTION 21A: Miscellaneous technical issues:
==============================================================================

Q118: Why are classes with static data members getting linker errors?

Static data members must be explicitly defined in exactly one module.  E.g.,

    class Fred {
    public:
      //...
    private:
      static int i_;  //declares static data member "Fred::i_"
      //...
    };

The linker will holler at you ("Fred::i_ is not defined") unless you define (as
opposed to declare) "Fred::i_" in (exactly) one of your source files:

    int Fred::i_ = some_expression_evaluating_to_an_int;
or:
    int Fred::i_;

The usual place to define static data members of class "Fred" is file "Fred.C"
(or "Fred.cpp", etc; whatever filename extension you use).

==============================================================================

Q119: What's the difference between the keywords struct and class?

The members and base classes of a struct are public by default, while in class,
they default to private.  Note: you should make your base classes EXPLICITLY
public, private, or protected, rather than relying on the defaults.

"struct" and "class" are otherwise functionally equivalent.

==============================================================================

Q120: Why can't I overload a function by its return type?

If you declare both "char f()" and "float f()", the compiler gives you an error
message, since calling simply "f()" would be ambiguous.

==============================================================================

Q121: What is "persistence"?  What is a "persistent object"?

A persistent object can live after the program which created it has stopped.
Persistent objects can even outlive different versions of the creating program,
can outlive the disk system, the operating system, or even the hardware on
which the OS was running when they were created.

The challenge with persistent objects is to effectively store their method code
out on secondary storage along with their data bits (and the data bits and
method code of all member objects, and of all their member objects and base
classes, etc).  This is non-trivial when you have to do it yourself.  In C++,
you have to do it yourself.  C++/OO databases can help hide the mechanism for
all this.

==============================================================================
SUBSECTION 21B: Miscellaneous environmental issues:
==============================================================================

Q122: Is there a TeX or LaTeX macro that fixes the spacing on "C++"?

Yes, here are two:

\def\CC{C\raise.22ex\hbox{{\footnotesize +}}\raise.22ex\hbox{\footnotesize +}}

\def\CC{{C\hspace{-.05em}\raisebox{.4ex}{\tiny\bf ++}}}

==============================================================================

Q123: Where can I access C++2LaTeX, a LaTeX pretty printer for C++ source?

Here are a few ftp locations:

Host aix370.rrz.uni-koeln.de   (134.95.80.1) Last updated 15:41 26 Apr 1991
    Location: /tex
      FILE      rw-rw-r--     59855  May  5  1990   C++2LaTeX-1.1.tar.Z
Host utsun.s.u-tokyo.ac.jp   (133.11.11.11) Last updated 05:06 20 Apr 1991
    Location: /TeX/macros
      FILE      rw-r--r--     59855  Mar  4 08:16   C++2LaTeX-1.1.tar.Z
Host nuri.inria.fr   (128.93.1.26) Last updated 05:23  9 Apr 1991
    Location: /TeX/tools
      FILE      rw-rw-r--     59855  Oct 23 16:05   C++2LaTeX-1.1.tar.Z
Host iamsun.unibe.ch   (130.92.64.10) Last updated 05:06  4 Apr 1991
    Location: /TeX
      FILE      rw-r--r--     59855  Apr 25  1990   C++2LaTeX-1.1.tar.Z
Host iamsun.unibe.ch   (130.92.64.10) Last updated 05:06  4 Apr 1991
    Location: /TeX
      FILE      rw-r--r--     51737  Apr 30  1990
      C++2LaTeX-1.1-PL1.tar.Z
Host tupac-amaru.informatik.rwth-aachen.de   (192.35.229.9) Last updated 05:07 18 Apr 1991
    Location: /pub/textproc/TeX
      FILE      rw-r--r--     72957  Oct 25 13:51  C++2LaTeX-1.1-PL4.tar.Z
Host wuarchive.wustl.edu   (128.252.135.4) Last updated 23:25 30 Apr 1991
    Location: /packages/tex/tex/192.35.229.9/textproc/TeX
      FILE      rw-rw-r--     49104  Apr 10  1990   C++2LaTeX-PL2.tar.Z
      FILE      rw-rw-r--     25835  Apr 10  1990   C++2LaTeX.tar.Z
Host tupac-amaru.informatik.rwth-aachen.de   (192.35.229.9) Last updated 05:07 18 Apr 1991
    Location: /pub/textproc/TeX
      FILE rw-r--r-- 74015  Mar 22 16:23 C++2LaTeX-1.1-PL5.tar.Z
    Location: /pub
      FILE rw-r--r-- 74015  Mar 22 16:23 C++2LaTeX-1.1-PL5.tar.Z
Host sol.cs.ruu.nl   (131.211.80.5) Last updated 05:10 15 Apr 1991
    Location: /TEX/TOOLS
      FILE      rw-r--r--     74015  Apr  4 21:02x   C++2LaTeX-1.1-PL5.tar.Z
Host tupac-amaru.informatik.rwth-aachen.de (192.35.229.9) Last updated 05:07 18 Apr 1991
    Location: /pub/textproc/TeX
      FILE      rw-r--r--      4792  Sep 11  1990 C++2LaTeX-1.1-patch#1
      FILE      rw-r--r--      2385  Sep 11  1990 C++2LaTeX-1.1-patch#2
      FILE      rw-r--r--      5069  Sep 11  1990 C++2LaTeX-1.1-patch#3
      FILE      rw-r--r--      1587  Oct 25 13:58 C++2LaTeX-1.1-patch#4
      FILE      rw-r--r--      8869  Mar 22 16:23 C++2LaTeX-1.1-patch#5
      FILE      rw-r--r--      1869  Mar 22 16:23 C++2LaTeX.README
Host rusmv1.rus.uni-stuttgart.de   (129.69.1.12) Last updated 05:13 13 Apr 1991
    Location: /soft/tex/utilities
      FILE      rw-rw-r--    163840  Jul 16  1990   C++2LaTeX-1.1.tar

==============================================================================

Q124: Where can I access "tgrind," a pretty printer for C++/C/etc source?

"tgrind" reads a C++ source file, and spits out something that looks pretty on
most Unix printers.  It usually comes with the public distribution of TeX and
LaTeX; look in the directory: "...tex82/contrib/van/tgrind".  A more up-to-date
version of tgrind by Jerry Leichter can be found on: venus.ycc.yale.edu in
[.TGRIND].

==============================================================================

Q125: Is there a C++-mode for GNU emacs?  If so, where can I get it?

Yes, there is a C++-mode for GNU emacs.  You can get it via:

c++-mode-2 (1.0)  87-12-08
     Bruce Eckel,Thomas Keffer, <[e-mail],uw-beaver!beluga!eckel,[e-mail]>
     archive.cis.ohio-state.edu:/pub/gnu/emacs/elisp-archive/as-is/c++-mode-2.el.Z

     Another C++ major mode.
c++-mode      89-11-07
     Dave Detlefs, et al, <[e-mail]>
     archive.cis.ohio-state.edu:/pub/gnu/emacs/elisp-archive/modes/c++-mode.el.Z

     C++ major mode.
c++          90-02-01
     David Detlefs, Stewart Clamen, <[e-mail],[e-mail]>
     archive.cis.ohio-state.edu:/pub/gnu/emacs/elisp-archive/modes/c++.el.Z
     C++ code editing commands for Emacs

c-support (46)      89-11-04
     Lynn Slater, <[e-mail]>
     archive.cis.ohio-state.edu:/pub/gnu/emacs/elisp-archive/misc/c-support.el.Z
     Partial support for team C/C++ development.

==============================================================================

Q126: Where can I get OS-specific FAQs answered (e.g.,BC++,DOS,Windows,etc)?

see comp.os.msdos.programmer, BC++ and Zortech mailing lists, BC++ and
   Zortech bug lists, comp.windows.ms.programmer, comp.unix.programmer, etc.

You can subscribe to the BC++ mailing list by sending email to:
|    To: [e-mail]   <---or [e-mail]
|    Subject: SUB TCPLUS-L
|    Reply-to: [e-mail]    <---i.e., put your return address here

The BC++ bug report is available via anonymous ftp from sun.soe.clarkson.edu
[128.153.12.3] from the file ~ftp/pub/Turbo-C++/bug-report
(also, I post it on comp.lang.c++ on the first each month).

Relevant email addresses:
    [e-mail]          General requests and discussion
    [e-mail]  Requests to be added to ztc-list
    [e-mail]          For _short_ bug reports

==============================================================================

Q127: Why does my DOS C++ program says "Sorry: floating point code not
   linked"?

The compiler attempts to save space in the executable by not including the
float-to-string format conversion routines unless they are necessary, but
sometimes it guesses wrong, and gives you the above error message.  You can fix
this by (1) using <iostream.h> instead of <stdio.h>, or (2) by including the
following function somewhere in your compilation (but don't call it!):

    static void dummyfloat(float *x) { float y; dummyfloat(&y); }

See FAQ on stream I/O for more reasons to use <iostream.h> vs <stdio.h>.

==============================================================================

--
Marshall Cline
--
Marshall P. Cline, Ph.D. / Paradigm Shift Inc / PO Box 5108 / Potsdam NY 13676
[e-mail] / 315-353-6100 / FAX: [phone]