整数除法在C ++ 11 [英] Integer Division in C++11

问题描述

我注意到C ++ 11的第5.6节的一些措辞更改。 （我正在查看草案C ++标准N3242，日期2011-02-28。）新的（草案）标准包括句子：

I was noticing some wording changes to section 5.6 for C++11. (I'm looking at the draft C++ standard N3242, dated 2011-02-28.) The new (draft) standard includes the sentence:

对于整数操作数/操作符产生代数商，任何小数部分都被丢弃;

"For integral operands the / operator yields the algebraic quotient with any fractional part discarded;"

这个语句不是03标准的5.6（ISO-IEC-14882-2003）不认为这是一个变化，是吗？这是C和C ++如何工作多年，除非我失去了我的想法（这可能已经发生了）。

This statement is not in 5.6 of the 03 standard (ISO-IEC-14882-2003), but I don't think this is a change, is it? This is how C and C++ has worked for years unless I've lost my mind (which may have happened anyway).

推荐答案

5.6 / 4 的脚注说：

[C ++ 03 footnote 74]：根据修订版本
C，用于整数除法的优选算法遵循在ISO Fortran标准ISO / IEC 1539：1991中定义的
规则，其中，商品总是舍入为零。

[C++03 footnote 74]: According to work underway toward the revision of ISO C, the preferred algorithm for integer division follows the rules defined in the ISO Fortran standard, ISO/IEC 1539:1991, in which the quotient is always rounded toward zero.

在C ++ 11中，这种行为是明确需要的，而不是preferred。更改列在兼容性部分中：

In C++11 this behaviour is explicitly required rather than being "preferred"; the change is listed in the compatibility section:

[C ++ 11：C.2.2] code>

更改：为整数 / 和％的结果指定舍入 对原始功能的影响使用整数除法的有效C ++ 2003代码
将结果四舍五入到0或负无穷大，而这个
国际标准总是将结果四舍五入到0.

[C++11: C.2.2]:
Change: Specify rounding for results of integer / and %
Rationale: Increase portability, C99 compatibility.
Effect on original feature: Valid C++ 2003 code that uses integer division rounds the result toward 0 or toward negative infinity, whereas this International Standard always rounds the result toward 0.

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