shift operator undefined behavior

Hi,

I was expecting:

int main( int argc, char *argv[] )
{
   unsigned char m = 32;
   register unsigned mask = (1<<m);
   std::cout << std::hex << mask << '\n';
   return 0;
}

to print 0 but instead this program compiled with g++ prints 1!

If I change (1<<m) by (1<<32) or if change the program for

int main( int argc, char *argv[] )
{
   unsigned char m = 31;
   register unsigned mask = (1<<m)<<1;
   std::cout << std::hex << mask << '\n';
   return 0;
}

it gives me the expected 0.

In the C++ standard document, section 5.8. It is written "The behavior
is undefined if the right operand is negative, or greater than or
equal to the length in bits of the promoted left operand."

The root for this behavior probably originates from C but I am really
curious why the standard makes the shift operator so unintuitive.

Greetings,
Olivier Langlois
http://www.olivierlanglois.net
http://blog.olivierlanglois.net

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