string - '0' 做什么(字符串是一个字符) [英] what does string - '0' do (string is a char)

问题描述

这是做什么的

while(*string) {
    i = (i << 3) + (i<<1) + (*string -'0');
    string++;
}

*string -'0'

the *string -'0'

它会删除字符值还是什么?

does it remove the character value or something?

推荐答案

这会从 string 指向的字符中减去字符 '0' 的 ASCII 码.所以，'0' - '0' 给你 0 等等，'9' - '0' 为您提供 9.

This subtracts from the character to which string is pointing the ASCII code of the character '0'. So, '0' - '0' gives you 0 and so on and '9' - '0' gives you 9.

整个循环基本上是手动"计算字符串string指向的十进制整数的数值.

The entire loop is basically calculating "manually" the numerical value of the decimal integer in the string string points to.

那是因为 i <<3 等价于 i * 8 和 i <<1 等价于 i * 2 并且 (i << 3) + (i<<1) 等价于 i *8 + i * 2 或 i * 10.

That's because i << 3 is equivalent to i * 8 and i << 1 is equivalent to i * 2 and (i << 3) + (i<<1) is equivalent to i * 8 + i * 2 or i * 10.

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