[英]What does “<<” (double angle brackets) mean in C/C++ enum?
enum ofp10_port_state {
OFPPS10_STP_LISTEN = 0 << 8, /* Not learning or relaying frames. */
OFPPS10_STP_LEARN = 1 << 8, /* Learning but not relaying frames. */
OFPPS10_STP_FORWARD = 2 << 8, /* Learning and relaying frames. */
OFPPS10_STP_BLOCK = 3 << 8, /* Not part of spanning tree. */
OFPPS10_STP_MASK = 3 << 8 /* Bit mask for OFPPS10_STP_* values. */
};
Its a left bit shift operator. 它是一个左移位运算符。 Meaning it shifts the bits left the indicated number of bits: 这意味着它将位移位指定的位数:
say that the value is: 说价值是:
0x0F or 00001111
0x0F << 4 = 0xF0 or 11110000
In microsoft c++ shifts right (>>) keep the sign (or the most significant digit, the one on the far left) depending on if the number is signed or unsigned 在microsoft c ++中右移(>>)保留符号(或最高位数,最左边的数字),具体取决于数字是有符号还是无符号
(assuming size of a byte): (假设一个字节的大小):
signed integer (an int for example):
0x80 or 10000000
0x80 >> 7 = 11111111
0x10 or 00010000
0x10 >> 4 = 00000001
if its unsigned (a uint):
0x80 or 10000000
0x80 >> 7 = 00000001
0x10 or 00010000
0x10 >> 4 = 00000001
<<
is a left bitshift operator. <<
是左移位运算符。
If you have a bit pattern like 0010
(2 in decimal) and shift it to the left by 2 like so 0010<<2
, you get 1000
(8 in decimal). 如果你有一个比特模式,如0010
(十进制2),并将它向左移动2,像0010<<2
,你得到1000
(十进制8)。
An enum is simply an integer that is large enough to hold at least an int
. 枚举只是一个足以容纳至少int
。 Thus we can directly assign int
values like 0, 1, etc. to it. 因此,我们可以直接为其分配0,1等int
值。
In this case, we are assigning things like 1 << 8
to it (which yields 100000000
or 256 in decimal). 在这种情况下,我们将1 << 8
分配给它(它产生100000000
或十进制的256)。
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