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yellowstone (62484)

yellowstone
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Journal of yellowstone (62484)

What is NULL?

[ #175169 ]
Tuesday June 26 2007, @02:48AM
Programming
This is the right:

#define NULL 0
This is wrong:

#define NULL ((void *)0)
Know why? In C++, this is supposed to be legal:

char *p = NULL;

With the first version, it is. With the second version, it's an error: there is no legal implicit conversion from void* to char*

<stddef.h>, <libio.h>, <glib/glib.h> -- I'm lookin' at you.


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  • interesting crap creeps up in c/c++ every day. i wish i had an ssh right now into my linux box, it would be interesting to see if this would work in straight C.

    • C is a lot more casual about pointer conversion than C++. Here's what I get on my system for

      void foo()
      {
      char *p = (void *)0;
      }

      $ gcc -c foo.c -Wall
      foo.c: in function `foo':
      foo.c:3: warning: unused variable `p'
      $ g++ -c foo.c -Wall
      foo.c: in fun

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