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From: kanze@gabi-soft.de
Subject: Re: cout << null pointers
Date: 2000/07/09
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Paul Meyerholtz <pholtz@ix.netcom.com> writes:

|>  I have found an inconsistent output by various compilers of the
|>  following:

|>  char * p =3D 0;
|>  cout * q =3D "";

|>  cout << p << "\n\n";
|>  cout << q;

|>  Most compilers seem to handle "cout << q" without a problem.  (But I
|>  have heard that Visual C++ 6 fails this test).

I'd be surprised.  I don't think any compiler would have a problem with
cout << q.

|>  However, the handling of "cout << p" seems to cause problems for
|>  most computers, with results from segment faults to garbage output.

Outputting a char* involves derefencing it.  Dereferening a null pointer
is undefined behavior.  Consider yourself lucky that it didn't reformat
your disk.

|>  Why is the output of p and q different?

Because the input is different.  Why should it be the same?  Why should
outputting a null pointer have any defined behavior?

|>  Is there anything in the standard about this?

That a program which attempts to output a null char* has undefined
behavior.  It is a programming error.

|>  Should cout check for the null pointer?

Why?  It could possibly check for a null pointer, but then, what about
all of the other illegal values?

--=20
James Kanze                               mailto:kanze@gabi-soft.de
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