问题描述
虽然clang编译了以下行，但g ++ 6.1抱怨数字分隔符(请参阅Coliru上的实时示例) :
While clang compiles the following line, g++ 6.1 complains about the digit separator (see live example on Coliru):
auto time = 01'23s;
哪个编译器(如果有)根据C ++ 14标准(N3796)是正确的?
Which compiler, if any, is correct according to the C++14 standard (N3796)?
否则，是否允许数字分隔符(第2.14.2节)只是<chrono>库(第20.12.5.8节)的用户定义文字(第2.14.8节)中的实现细节?恕我直言，不应该这样，因为这些文字是在unsigned long long参数上定义的.
Otherwise, is allowing digit separators (§2.14.2) just an implementation detail in the user-defined literals (§2.14.8) of the <chrono> library (§20.12.5.8)? IMHO it should be not, since these literals are defined on unsigned long long parameters.
我记得Howard Hinnant在 CppCon 2016演讲中以10'000s为例<chrono>教程" (在他的演讲中大约有42分钟的时间.)
I remember Howard Hinnant using 10'000s as an example during his CppCon 2016 talk "A <chrono> tutorial" (at about 42 minutes in his talk).
(请注意，我不打算编写"1分23秒"的代码，这只是偶然地纠正，因为八进制字面0123是64 + 16 + 3 == 83为此，我应该写
(Please note, that I did not intend to code "1 minute and 23 seconds", which is only correct by accident, since the octal literal 0123 is 64 + 16 + 3 == 83. For that purpose I should write
auto time = 1min + 23s;
但是可能的误导性解释不是问题的一部分.)
but that possible misleading interpretation is not part of the question.)
推荐答案
如果您查看语法，则 user-defined-integer-literal 可以是 octal-literal ud-suffix ，而八进制被定义为0或八进制'八进制.
If you look at the grammar, user-defined-integer-literal can be octal-literal ud-suffix, and octal-literal is defined as either 0 or octal-literal ’ octal-digit.
用户定义的文字:
- 用户定义的整数文字
- [...]
- user-defined-integer-literal
- [...]
用户定义的整数文字:
- 八进制文字ud后缀
- [...]
- octal-literal ud-suffix
- [...]
八进制:
-
0 - 八进制文字‘八进制数字
0- octal-literal ’ octal-digit
所以01'23s是完全有效的文字.
So 01'23s is a perfectly valid literal.
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