c++ - 具有负值的模运算符

Question

这个问题已经有答案了:

Why does C++ output negative numbers when using modulo? (4 个回答)

已关闭 4 年前。

为什么要进行这样的操作:

std::cout << (-7 % 3) << std::endl;
std::cout << (7 % -3) << std::endl;

给出不同的结果？

-1
1

Answer 1

来自 ISO14882:2011(e) 5.6-4:

The binary / operator yields the quotient, and the binary % operatoryields the remainder from the division of the first expression by thesecond. If the second operand of / or % is zero the behavior isundefined. For integral operands the / operator yields the algebraic quotient with any fractional part discarded; if the quotient a/b isrepresentable in the type of the result, (a/b)*b + a%b is equal to a.

剩下的就是基本数学:

(-7 / 3) => -2
-2 * 3   => -6
so a % b => -1

(7 / -3) => -2
-2 * -3  => 6
so a % b => 1

请注意

If both operands are nonnegative then the remainder is nonnegative; ifnot, the sign of the remainder is implementation-defined.

ISO14882:2003(e) 中的内容不再出现在 ISO14882:2011(e) 中