在以下情况下，如何计算按位运算符结果的总和？

Question

The code is as follows:

#include <stdio.h>
int main()
{
    int a = 512,b = 32;
    int c = a>>2 + b<<2;
    printf("%d",c);

    return 0;
}

The result I'd expect isn't 512 and rather 128 (a>>2) + 128 (b<<2) as the result. Why is the output 512? I understand that arithmetic + operator has higher precedence but where does the brackets land? Any help is appreciated, thanks.

Answer 1

Operator precedence in C states that additive operators have a higher precedence than shifting operators, if you want the expected output of 256 you will need to use parenthesis to force shifting to take place first. So, int c = a>>2 + b<<2; becomes int c = (a>>2) + (b<<2);

As stated in the comments (by @Eugene Sh.), currently it is evaluated as (a>>(2+b)) << 2) and that is undefined behavior, as you are shifting more than the type width.