我在使用msdev 2010时遇到了一些__int64类型的奇怪行为。是否有人能够告诉我发生了什么? 我猜这里有两个问题,首先是如何显示64位整数,其次是行为-即为什么看起来像__int64实际上是32位整数...
#include <stdio.h>
int main()
{
int vl_idx;
unsigned __int64 vl_64;
unsigned __int64 vl_64_test;
for (vl_idx = 0; vl_idx < 64; vl_idx++)
{
vl_64 = 1 << vl_idx;
printf ("vl_64 (%d) = %I64u\n", vl_idx, vl_64);
printf ("vl_64 (%d) = %llu\n", vl_idx, vl_64);
printf ("vl_64 (%d) = %lu\n", vl_idx, vl_64);
}
vl_64_test = 1 << 31;
if (vl_64 > vl_64_test)
printf ("greater\n");
if (vl_64 == vl_64_test)
printf ("equal\n");
if (vl_64 < vl_64_test)
printf ("less\n");
return 0;
}
前30次迭代的输出结果如预期:
vl_64 (0) = 1
vl_64 (0) = 1
vl_64 (0) = 1
vl_64 (1) = 2
vl_64 (1) = 2
vl_64 (1) = 2
...
vl_64 (30) = 1073741824
vl_64 (30) = 1073741824
vl_64 (30) = 1073741824
vl_64 (31) = 18446744071562067968
vl_64 (31) = 18446744071562067968
vl_64 (31) = 2147483648
vl_64 (32) = 1
vl_64 (32) = 1
vl_64 (32) = 1
vl_64 (33) = 2
vl_64 (33) = 2
vl_64 (33) = 2
...
vl_64 (62) = 1073741824
vl_64 (62) = 1073741824
vl_64 (62) = 1073741824
vl_64 (63) = 18446744071562067968
vl_64 (63) = 18446744071562067968
vl_64 (63) = 2147483648
equal
但是,在第32次迭代时,事情发生了“溢出”。这可能只是一个显示问题,但结尾处的比较表明情况并非如此。
这是使用msdev 2010 cl(64位版本)编译,并在64位Windows操作系统上运行(具有64位CPU)。有什么建议可以解释为什么比较会认为1<<31 == 1<<63?
感谢任何建议,
Jim