~

[Bitwise Operators]

描述

The bitwise NOT operator in C++ is the tilde character ~. Unlike & and |, the bitwise NOT operator is applied to a single operand to its right. Bitwise NOT changes each bit to its opposite: 0 becomes 1, and 1 becomes 0. For example:

0    1      operand1
———-
1    0      ~ operand1

範例程式碼

int a = 103;    // binary:  00000000000000000000000001100111
int b = ~a;     // binary:  11111111111111111111111110011000 = -104

Tips

You might be surprised to see a negative number like -104 as the result of this operation. This is because the highest bit in an int variable is the so-called sign bit. If the highest bit is 1, the number is interpreted as negative. This encoding of positive and negative numbers is referred to as two’s complement. For more information, see the Wikipedia article on two’s complement.

As an aside, it is interesting to note that for any integer x, ~x is the same as -x-1.

At times, the sign bit in a signed integer expression can cause some unwanted surprises.

參考

• [Example] BitMath Tutorial

語法參考主頁面

86Duino 參考的文本是根據 知識共享署名-相同方式分享 3.0 許可證，部分文本是從 Arduino 參考 修改的。 參考中的代碼示例已發佈到公共領域。