0是十进制文字还是八进制文字？

Question

零永远是零，所以没关系。但是在最近与一位朋友的讨论中，他说八进制文字如今几乎没有使用。†然后我发现实际上我的代码中几乎所有整数文字都是八进制的，即0。

0根据C ++语法，八进制文字是否正确？标准怎么说？

†我知道的唯一真正用途是用于UNIX文件权限

Answer 1

是的，0是C ++中的八进制文字。根据C ++标准：2.14.2整数文字[lex.icon]integer-literal:&nbsp;&nbsp;&nbsp; &nbsp; decimal-literal integer-suffixopt&nbsp;&nbsp;&nbsp; &nbsp; octal-literal integer-suffixopt&nbsp;&nbsp;&nbsp; &nbsp; hexadecimal-literal integer-suffixopt&nbsp;&nbsp;decimal-literal:&nbsp;&nbsp;&nbsp; &nbsp; nonzero-digit&nbsp;&nbsp;&nbsp; &nbsp; decimal-literal digit&nbsp;&nbsp;octal-literal:&nbsp;&nbsp;&nbsp; &nbsp; 0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<--------------------<Here>&nbsp; &nbsp; octal-literal octal-digit

Answer 2

任何带前缀的整数值0都是八进制值。即：01是八进制数1，010是八进制数10，即十进制数8，而0是八进制数0（即十进制数，其他为0）。所以是的，“ 0”是八进制。那是@Als的答案中语法片段的简单英语翻译:-)一个整数前缀0x是没有前缀0。0x是一个明显不同的前缀。显然有些人无法做出这种区分。按照相同的标准，如果我们继续：&nbsp;integer-literal:&nbsp; &nbsp; &nbsp;decimal-literal integer-suffixopt&nbsp; &nbsp; &nbsp;octal-literal integer-suffixopt&nbsp; &nbsp; &nbsp;hexadecimal-literal integer-suffixopt&nbsp;decimal-literal:&nbsp; &nbsp; &nbsp;nonzero-digit&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<<<---- That's the case of no prefix.&nbsp; &nbsp; &nbsp;decimal-literal digit-separatoropt digit&nbsp;octal-literal:&nbsp; &nbsp; &nbsp;0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <<<---- '0' prefix defined here.&nbsp; &nbsp; &nbsp;octal-literal digit-separatoropt octal-digit <<<---- No 'x' or 'X' is&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; allowed here.&nbsp;hexadecimal-literal:&nbsp; &nbsp; &nbsp;0x hexadecimal-digit&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<<<---- '0x' prefix defined here&nbsp; &nbsp; &nbsp;0X hexadecimal-digit&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<<<---- And here.&nbsp; &nbsp; &nbsp;hexadecimal-literal digit-separatoropt hexadecimal-digit

Answer 3

显然所有以零开头的整数文字都是八进制的。这意味着它也包括0。由于零为零，因此差异不大。但是不知道这个事实会伤害您。当我尝试编写将二进制数字转换为十进制和十六进制输出的程序时，我意识到了这一点。每当我给出从零开始的数字时，我都会得到错误的输出（例如012 = 10，而不是12）。很高兴知道这些信息，这样您就不会犯同样的错误。