c - 三元运算符

Question

unsigned char result= 0x0;
int maxX,maxY;
maxX = maxY = 0;
printf("enter input\n");
scanf("%d",&maxX);
scanf("%d",&maxY);
(maxX < 200)?(result | (1 )) :0;
(maxX > 1500)?(result | (1 <<1  )) :0;
(maxY < 200)?(result | (1 <<2  )) :0;
(maxY > 1500)?(result | (1 << 3)) :0;

printf("Result is %d\n",result);

为什么无论 maxX 和 maxY 输入如何，result 始终为零？

Answer 1

您正在计算三元运算符，但没有将它们分配给任何东西。这:

(result | (1 ))

获取 result 并将其与 1 进行或运算，但不对结果执行任何操作。

如果你用-Wall -Wextra编译，它会警告你:

/tmp/x1.c: In function ‘main’:
/tmp/x1.c:12: warning: statement with no effect
/tmp/x1.c:13: warning: statement with no effect
/tmp/x1.c:14: warning: statement with no effect
/tmp/x1.c:15: warning: statement with no effect

如果您希望获取该结果并将其分配回 result，请执行以下操作:

result |= (maxX < 200)?(1) :0;
result |= (maxX > 1500)?(1 <<1 ) :0;
result |= (maxY < 200)?(1 <<2 ) :0;
result |= (maxY > 1500)?(1 << 3) :0;