向左移位 3 如何得到以字节为单位的位数？

Question

我正在学习位打包和位缓冲区，我遇到了这行代码

int NumBits = sizeof(float) << 3

现在输出是正确的，浮点数是 4 个字节，当你将其转换为位时，它是 32 位，这就是

NumBits

的值

我的问题是向左移位 3 位如何给出正确的值？

他们也可以用相反的方式做到这一点，将实际的

NumBits

向右移动 3

int numbytes = NumBits >> 3;

Answer 1

sizeof(float) 返回浮点数的大小（以字节为单位）。在大多数系统（例如 PC）中，一个 float 为 4 个字节，因此 sizeof(float) 等于 4。

<< operator is the left shift operator. When you left-shift a value by a certain number of bits, you effectively multiply the value by 2 raised to the power of the number of bits shifted. In this case, you are left-shifting by 3 bits, so it's equivalent to multiplying by 2^3, which is 8.

所以，sizeof(float) << 3 is equivalent to 4 << 3, which is equal to 32. In summary, shifting to the left by 3 is same as multiplying with 8, which gives the number of bits.