Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!cos.com!patrick
From: patrick@cos.com (Patrick Steranka)
Newsgroups: gnu.g++.bug
Subject: Can't assign 'this' in a constructor
Message-ID: <8912022231.AA26818@qna.cos.com>
Date: 2 Dec 89 22:31:38 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
Organization: GNUs Not Usenet
Lines: 60

In BS, pg 164, 5.5.6 it states:

	The assignment to "this" [in a constructor function] informs
	the compiler that the programmer has taken control and that the
	default mechanism for allocating storage should not be used.

This does not seem to be supported by the GNU g++ compiler.
Instead, the error

	assignment of read-only parameter `$this'

is produced.  Below is a sample program and the output produced
when compiling it.  This happens on a SUN 3/280 running SUN OS
3.5 using g++(1.36.1).

==============================   ex7.cc  ==============================
#include <stream.h>
class T{
    char s[10];
 public:
    T() {
	if (this == 0) this = (T*) 0x43;
	cout << "Value of 'this' is " << (int)this << "\n";
    };
    ~T() {
	cout << "In ~T, the value of 'this' is " << (int)this << "\n";
        this = 0;
    }
};

main(int argc, char* argv[])
{
    T a1;
}
==============================   ex7.cc  ==============================


====================  Output from compiling ex7.cc  ====================
cd /usr.MC68020/zulu/patrick/test/c++/
make -k ex7
g++ -o ex7 -g -v ex7.cc
gcc version 1.36.1- (based on GCC 1.36)
 /usr/local/lib/gnu/gcc/gcc-cpp -+ -v -undef -D__GNUC__ -D__GNUG__ -D__cplusplus -Dmc68000 -Dsun -Dunix -D__mc68000__ -D__sun__ -D__unix__ -D__HAVE_68881__ -Dmc68020 ex7.cc /usr/tmp/cca21893.cpp
GNU CPP version 1.36
 /usr/local/lib/gnu/gcc/gcc-cc1plus /usr/tmp/cca21893.cpp -quiet -dumpbase ex7.cc -g -version -o /usr/tmp/cca21893.s
GNU C++ version 1.36.1 (based on GCC 1.36) (68k, MIT syntax) compiled by GNU C version 1.36.
default target switches: -m68020 -mc68020 -m68881 -mbitfield
ex7.cc: In method T::T ():
ex7.cc:6: assignment of read-only parameter `$this'
*** Error code 1
make: Fatal error: Target `ex7' not remade because of errors

Compilation exited abnormally with code 1 at Sat Dec  2 17:25:34
====================  Output from compiling ex7.cc  ====================


patrick (Patrick Steranka @ Corporation for Open Systems)
	-- patrick@cos.com
	-- patrick%cos.com@uunet.uu.net
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