sizeof

原文链接： http://www.cnblogs.com/RascallySnake/p/3185071.html 在掌握了socket相关的一些函数后，套接字编程还是比较简单的，日常工作中碰到很多的问题就是客户端/服务器模型中，如何让服务端在同一时间高效的处理多个客户端的连接，我们的处理办法可能会是在服务端不停的监听客户端的请求，有新的请求到达时，开辟一个新的线程去和该客户端进行后续处理，但是这样针对每一个客户端都需要去开辟一个新的线程，效率必定底下。 其实，socket编程提供了很多的模型来处理这种情形，我们只要按照模型去实现我们的代码就可以解决这个问题。主要有select模型和重叠I/o模型，以及完成端口模型。这次，我们主要介绍下select模型，该模型又分为普通select模型，wsaasyncselect模型，wsaeventselect模型。我们将通过样例代码的方式逐一介绍。 一、select模型 使用该模型时，在服务端我们可以开辟两个线程，一个线程用来监听客户端的连接 请求，另一个用来处理客户端的请求。主要用到的函数为select函数。如： 全局变量： fd_set g_fdClientSock; 线程1处理函数： SOCKET listenSock = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP ); sockaddr_in

I know that the C++ standard explicitly guarantees the size of only char , signed char and unsigned char . Also it gives guarantees that, say, short is at least as big as char , int as big as short etc. But no explicit guarantees about absolute value of, say, sizeof(int) . This was the info in my head and I lived happily with it. Some time ago, however, I came across a comment in SO (can't find it) that in C long is guaranteed to be at least 4 bytes, and that requirement is "inherited" by C++. Is that the case? If so, what other implicit guarantees do we have for the sizes of arithmetic types

From [5.3.3/1] , I found that: The sizeof operator shall not be applied to an expression that has function or incomplete type From [3.9/5] I found that: Incompletely-defined object types and cv void are incomplete types Anyway, for sizeof does not evaluate it's operands, I would have said that sizeof(void()) was a legal expression (actually GCC compiles it and the result is 1). On the other side, from here , void is not mentioned while discussing sizeof , neither when the types having size 1 are mentioned, nor in the list of the ones having an implementation defined size. The question is thus:

1 题目描述 　　求1+2+3+...+n，要求不能使用乘除法、for、while、if、else、switch、case等关键字及条件判断语句（A?B:C）。 2 思路和方法 　　（1）递归，不能使用if等条件判断语句，可以使用&&逻辑运算符的短路特性实现。 当n=0时，不进行后一个判断的计算，作为递归终止 。 　　（2）利用sizeof(a)计算bool数组的字节数，bool类型在C++中占一个字节。bool a = [n][n+1]; 因一共有n*(n+1)个1，下三角或者上三角，第一行：[1]和为1；第二行：[1][1] 和为2；第三行：[1][1][1]和为3，……。bool类型的数据a，sizeof(a)=n*(n+1)，所以1+2+3+...+n=sizeof(a)=n*(n+1)/2，或者是sizeof(a)>>1。 3 C++核心代码 1 #include<iostream> 2 3 #include<vector> 4 5 using namespace std; 6 7 class Solution { 8 public: 9 int Sum_Solution(int n) { 10 int sum = n; 11 sum && (sum += Sum_Solution(n - 1));// 利用前一个判断短路；当n=0时，不进行后一个判断的计算，作为递归终止

// 面试题23：链表中环的入口结点 // 题目：一个链表中包含环，如何找出环的入口结点？例如，在图3.8的链表中， // 环的入口结点是结点3。 ListNode* FindFirstNode(ListNode* HeadNode) { if(!HeadNode) return nullptr; ListNode* FastNode = HeadNode; ListNode* SlowNode = HeadNode; while(FastNode&(FastNode->NextPoint)) { SlowNode = SlowNode->NextPoint; FastNode = SlowNode->NextPoint; if(FastNode == SlowNode) { SlowNode = HeadNode; while(FastNode != SlowNode) { FastNode = FastNode->NextPoint; SlowNode = SlowNode->NextPoint; } return SlowNode; } } return nullptr; } //找到链表中环形链表的入口点 ListNode* FindTheFirstNode(ListNode* Node) { if(Node ==nullptr) return nullptr;

1，结构体中内存的对齐 #include "pch.h" #include <iostream> struct Test { int a; // 4 short b; // 2 char c; // 1 double d; // 8 }; int main() { Test t; t.a = 100; t.b = 200; t.c = 'c'; t.d = 10.11; printf("sizeof(Test) = %d\n",sizeof(t)); std::cout << "Hello World!\n"; } 将结构体中数据位置换一下： #include "pch.h" #include <iostream> struct Test { int a; // 4 double d; // 8 short b; // 2 char c; // 1 }; int main() { Test t; t.a = 100; t.b = 200; t.c = 'c'; t.d = 10.11; printf("sizeof(Test) = %d\n",sizeof(t)); std::cout << "Hello World!\n"; } 2，结构体中含有结构体的内存对齐 3，含有位域的内存对齐 　　 每个特定平台上的编译器都有自己的默认“对齐系数”(也叫对齐模数)。

Possible Duplicates: Empty class in C++ What is the size of an empty struct in C? I read somewhere that size of an empty struct in C++ is 1. So I thought of verifying it. Unfortunately I saved it as a C file and used <stdio.h> header and I was surprised to see the output. It was 0. That means struct Empty { }; int main(void) { printf("%d",(int)sizeof(Empty)); } was printing 0 when compiled as a C file and 1 when compiled as a C++ file. I want to know the reason. I read that sizeof empty struct in c++ is not zero because if the size were 0 two objects of the class would have the same address