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From: minar@reed.bitnet (Nelson Minar,L08,x640,7776519)
Newsgroups: comp.os.msdos.programmer,comp.lang.c++
Subject: Possible bug in Turbo C++ dealing with inline functions returning
Summary: should this work?
Message-ID: <15588@reed.UUCP>
Date: 21 Oct 90 22:38:09 GMT
Sender: news@reed.UUCP
Reply-To: minar@reed.bitnet (Nelson Minar)
Followup-To: comp.os.msdos.programmer
Organization: Reed College, Portland, OR
Lines: 75
Sender:

I have encountered something extemely nondesirable about how Turbo C++
1.0 handles inline functions returning class instances.  It seems to get
very confused about them, and won't compile conditionals complaining
about required destructors (explicitly declaring a destructor is no
help).  g++ 1.37.1 has no trouble at all compiling this same piece of
code.

Here is the error output of tcc:

inlines.cpp:
Error inlines.cpp 13: Destructor for Foo required in conditional expression
  in function test(int)
Error inlines.cpp 13: Destructor for Foo required in conditional expression
  in function test(int)

and here is the program:

// This compiles under g++ 1.37.1, but will not compile in Turbo C++ 1.0
// with the compilation options '-y -v -vi- -N' or '-y -v -vi -N'

#include <stdio.h>

class Foo {
public:
  Foo() {}                                       // plain constructor
  Foo(int x) { value = x; }                      // constructor taking an int
  operator int() { return value; }               // conversion
  int value;
};

inline Foo
test (int input) {
  return input == 1 ? Foo (4) : Foo (3);         // line 13 - return a Foo
}                                                // depending on input

void main() {
  Foo testVal;
  testVal = test(0);                             // testVal should be Foo(3)
  printf ("%d", int(testVal));                   // g++ gives expected answer
}


Even weirder, this program will compile fine without inlining functions
('-vi-') but will give the same "Destructor required" errors when
compiled with inlining functions ('-vi'), IF the conditional expression

  return input == 1 ? Foo (4) : Foo (3);

is turned into the equivalent if-then construct:

  if (input == 1)
    return Foo(4);
  else
    return Foo(3);

Not very useful, as I still can't inline the function.

it will also compile ok if there are not multiple return points in the
inlined function, say

  return Foo(input);

Is this a bug, is it me being stupid about trying to learn C++, or just
another 'interpretation' of the C++ 2.0 standard like Borland's for loop
thing is?  Its excessively annoying, as the function I am trying to
inline really needs to be inlined. I think I'll have to switch to a
macro, or some ugly function-with-side-effect answer.

I haven't tried to get to tech support yet, partially because their tech
support is a real pain, and partially because I do not know how to get
Borland a copy of the source code.  Is there ANY address on the Net that
will get to a Borland tech? I don't care if I have to wait for a snail-
mail reply...
__
\/ minar@reed.bitnet                         You know in your heart its flat.