ofstream bug in 2.1

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2 total messages Started by Wayne A. Christopher Tue, 29 Sep 1992 18:39

#302

Author: Wayne A. Christopher
Date: Tue, 29 Sep 1992 18:39

33 lines
1293 bytes

The following program causes an assertion failure in the ofstream
code.  I can't see what is wrong...  Any ideas?  I don't have 2.2 yet
so I haven't tested it there.

foo.cc:

#include <fstream.h>

static ofstream ofile;

main()
{
    ofile = ofstream("outputfile");    
    ofile << "Here is some output\n";
}

What happens:

% gcc-2.2.2 foo.cc -lg++-2_1
% gdb a.out
(gdb) run

Program received signal 6, Abort
0xf775f458 in kill ()
(gdb) where
#0  0xf775f458 in kill ()
#1  0xf77776fc in abort ()
#2  0xb93c in __overflow (sb=0x16650, c=72) at streambuf.C:186
#3  0xba4c in streambuf::sputn (this=0x16650, s=0x22a1 "ere is some output\n", 
    n=20) at streambuf.C:211
#4  0x5aa0 in operator<< (stream=@0x145b0, s=0x22a0 "Here is some output\n")
    at iostream.C:525
#5  0x2358 in main ()

Re: ofstream bug in 2.1

#306

Author: Joe Buck
Date: Thu, 01 Oct 1992 00:37

44 lines
1967 bytes

In article <1aa7sjINN2rj@agate.berkeley.edu> faustus@ygdrasil.cs.berkeley.edu (Wayne A. Christopher) writes:
>The following program causes an assertion failure in the ofstream
>code.  I can't see what is wrong...  Any ideas?  I don't have 2.2 yet
>so I haven't tested it there.

The crash also occurs with libg++ 2.2.

>#include <fstream.h>
>
>static ofstream ofile;
>
>main()
>{
>    ofile = ofstream("outputfile");    
>    ofile << "Here is some output\n";
>}

Since there is no assignment operator for class ofstream, or for any of
its baseclasses, the assignment of ofstream("outputfile") does a
memberwise copy of fields to ofile.  Since the right-side ojbect is a
temporary object, it is then destroyed, leaving ofile's members pointing
to garbage.  It is then only a matter of time until the program blows up.
Assigning one ofstream to another is not valid.

The iostream library provided with cfront 2.1 handles this by making
ios::operator= a private member, which makes assignment of iostream
objects a compile-time error (except for classes like
{i,o,io}stream_withassign, which provide an assignment operator).
I think that libg++ should either do the same, or provide a correct
assignment operator.  Same for the copy constructor.

libg++ does not provide the iostream_withassign classes.  Should it?
I don't know.

You can probably get the effect you wanted by saying

	ofile.open("outputfile");

--
Joe Buck	jbuck@ohm.berkeley.edu

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