c++ - "<<"(双尖括号)在 C/C++ 枚举中是什么意思？

Question

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. */

};

Answer 1

它是一个左移位运算符。这意味着它将位向左移动指定的位数:

假设值为:

0x0F or 00001111
0x0F << 4 = 0xF0 or 11110000

在 Microsoft C++ 中，右移 (>>) 保留符号(或最重要的数字，最左边的数字)取决于数字是有符号还是无符号

(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