zoukankan      html  css  js  c++  java
  • c++ / c 数值类型的一些感悟

    Contrary to the other answers, there is no undefined behavior here, and there is no overflow. Unsigned integers use modulo 2n arithmetic.

    Section 4.7 paragraph 2 of the standard says "If the destination type is unsigned, the resulting value is the least unsigned integer congruent to the source integer (modulo 2n where n is the number of bits used to represent the unsigned type)." This dictates that -1 is equal to the largest possible unsigned int (modulo 2n).

    Section 3.9.1 paragraph 4 says "Unsigned integers, declared unsigned, shall obey the laws of arithmetic modulo 2n where n is the number of bits in the value representation of that particular size of integer." To make it clear what this means, the footnote to this clause says "This implies that unsigned arithmetic does not overflow because a result that cannot be represented by the resulting unsigned integer type is reduced modulo the number that is one greater than the largest value that can be represented by the resulting unsigned integer type."


    In other words, converting -1 to 4294967295 is not just defined behavior, it is required behavior (assuming 32 bit integers). Similarly, adding 3 to that value and yielding 2 as a result is also required behavior. In this case, the value of n is irrelevant. The third value printed by hello() must be 2 or the implementation is not compliant with the standard.

  • 相关阅读:
    深入理解PHP原理之变量作用域
    深入理解PHP原理之变量分离/引用
    关于哈希表
    foreach 相关
    Scrapyd-Client的安装
    Scrapyd API的安装
    scrapyd的安装
    快手的小视频爬取
    实现单例模式的几种方式
    京东图书分布式爬虫
  • 原文地址:https://www.cnblogs.com/yetanghanCpp/p/8945109.html
Copyright © 2011-2022 走看看