从零开始的数字有什么特别之处？ [英] What is special about numbers starting with zero?

问题描述

这是一个愚蠢的问题，但对我来说很有趣）

This is kinda stupid question, but it's interesting for me )

这是我在Visual Studio 2013中得到的东西

This is what i get with visual studio 2013

int i = 07;     // i == 7
int i = 16;     // i == 16
int i = 00016;  // i == 14, why?
int i = 05016;  // i == 2574, wow )
int i = 08;     // compile error, compiler expects octal number...

如果数字以零开头且包含8，这是编译错误。这正常吗？以及如果00016 == 14，编译器到底从零开始做什么？

If number starts with zero and contains 8, it's compile error. Is this normal? And what exactly compiler does with starting zeros if 00016 == 14?

感谢所有人））

推荐答案

是的，这是预期的。

[C ++ 11：2.14 .2 / 1]： 整数文字是没有句号或指数部分的数字序列。整数文字可以具有指定其基数的前缀和指定其类型的后缀。数字序列的词法上的第一个数字是最高有效的。 十进制整数文字（以10为底）以非0的数字开头，并由一系列十进制数字组成。 八进制整数文字（以8为底）以数字0开头，由八进制数字序列组成。 ²² 一个十六进制整数文字（基数为16）以0x或0X开头，由一系列十六进制数字组成，其中包括十进制数字以及字母a至f和a至f，十进制值为10至15。 [示例：可以将数字十二写为12、014或0XC。 -结束示例]

[C++11: 2.14.2/1]: An integer literal is a sequence of digits that has no period or exponent part. An integer literal may have a prefix that specifies its base and a suffix that specifies its type. The lexically first digit of the sequence of digits is the most significant. A decimal integer literal (base ten) begins with a digit other than 0 and consists of a sequence of decimal digits. An octal integer literal (base eight) begins with the digit 0 and consists of a sequence of octal digits.²² A hexadecimal integer literal (base sixteen) begins with 0x or 0X and consists of a sequence of hexadecimal digits, which include the decimal digits and the letters a through f and A through F with decimal values ten through fifteen. [ Example: the number twelve can be written 12, 014, or 0XC. —end example ]

^{22 数字8和9不是八进制数字。}

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