#48. 注意避免移位过大

片段

  1 #include <stdio.h>
  2
  3 int main( int argc , char **argv )
  4 {
  5 unsigned int w = 32;
  6         printf("1U << w : 0x%x\n" , 1U << w );
  7
  8         return 0;
  9 }
 10

在x86上 , 根据编译时是否进行优化 , 运行结果也不同

05:21:30-xuk@localhost:~/svn/goodbyeworld/binary-hacks/48$gcc main.c
05:21:46-xuk@localhost:~/svn/goodbyeworld/binary-hacks/48$./a.out
1U << w : 0x1


05:22:14-xuk@localhost:~/svn/goodbyeworld/binary-hacks/48$gcc -O2 main.c
05:22:54-xuk@localhost:~/svn/goodbyeworld/binary-hacks/48$./a.out
1U << w : 0x0