Re: Does the null-pointer-constant occupy storage?
On Wed, 5 Aug 2009 14:40:42 CST, "/dev/null" <jorka2@hotmail.com>
wrote in comp.lang.c++.moderated:
Consider the following program.
#include <stdio>
Perhaps you meant either <cstdio> or <stdio.h>. There us no standard
header named <stdio> in C++, or C for that matter.
const int NULL = 0; // Recommended NULL definition according to The C+
+ Programming Language by Bjarne Stroustrup.
It's been a long, long time since I read the book, and nothing more
recent than the third edition at that. But I really rather doubt that
he actually recommended that you define NULL as a const int. In any
case, the C++ language standard overrides the book, and that requires
that NULL be a macro defined as an integer constant expression with a
value or 0.
If you did not mean either of the standard headers above, then all
best are off. Well most best. If you did, then you've got a program
that won't compile, since either <cstdio> or <stdio.h> defines NULL as
a macro that will break your definition of an int with the same name.
// function that changes NULL.
void foo( void )
{
int *p = const_cast<int32 *>(&NULL);
Why should we believe that an "int32" is an any way compatible with an
int. If an "int32" is a different type than int, the next line has
undefined behavior
*p = 42;
Assuming your program actually compiled (did you even try?), it is
undefined behavior to attempt to modify an object defined as const.
}
// Print value of NULL.
void print_null( void )
{
std::cout << NULL;
}
int main( void )
{
foo();
print_null();
}
Is this a well-formed C++ program?
If so, what will it print?
I neither know nor care what it will print, nor does the C++ standard,
since the code is ill-formed and the behavior undefined.
Best regards,
/J
Next time at least make sure your test program actually compiles,
please.
--
Jack Klein http://JK-Technology.Com
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