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A "unsigned long long " problem
- From: bacmoz <wg_nwpu at yahoo dot com dot cn>
- To: gcc-help at gcc dot gnu dot org
- Date: Mon, 31 Jul 2006 07:57:42 -0700 (PDT)
- Subject: A "unsigned long long " problem
my cpu is amd x86-64, and os is fedora core 5 x86-64 version
gcc version 4.1.0
the program lists here
#include "stdio.h"
int main(int argc, char* argv[])
{
unsigned long long a, b;
a = 0x8000000000000000;
b = a>>1;
printf(
"a = %llu\n"
"b = %llu\n",
a, b);
a = 1<<(8 * sizeof(unsigned long long) - 1); // here give a warning
b = a>>1;
printf(
"a = %llu\n"
"b = %llu\n",
a, b);
return 0;
}
the compiler gives a warning that left shift length is more than or equal to
type width.
the result is:
a = 9223372036854775808
b = 4611686018427387904
a = 0
b = 0
use gdb, "p/t 1<<63", the result is
1000000000000000000000000000000000000000000000000000000000000000, this is
right
"p a = 1<<63", then a is
1000000000000000000000000000000000000000000000000000000000000000
i don't know why i cannot get 1<<63 in my c program.
if change the type "unsigned long long" to "unsigned int", the result is ok.
--
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