/**************************@author: weedge@date: 21/07/2011@comment:1.不用局部变量和全局变量实现strlen；参考http://www.cppblog.com/ant/archive/2007/10/12/32886.html2.有2数据，写一个交换数据的宏 *******************************************/ #include <iostream>using namespace std;//========================swap===================================/*不能处理浮点数*/#define swap1(a,b) {a=a^b;b=a^b;a=a^b;}/*会出现溢出情况*/#define swap11(a,b) {a=a+b;b=a-b;a=a-b;}#define swap111(a,b) {a=a+b;b=a-b;a=a-b;}/*单精度浮点数情况*/#define US(x) (*(unsigned*)(&x)) //按无符号数读取x所在内存单元。#define swap2(a,b) {US(a) = US(a) ^ US(b); US(b) = US(a) ^ US(b); US(a) = US(a) ^ US(b);}/*双精度浮点数情况。*/#define USLL(x) (*(unsigned long long*)(&x)) //按64位无符号数读取x所在内存单元。#define swap3(a,b)\ { USLL(a) = USLL(a) ^ USLL(b);\USLL(b) = USLL(a) ^ USLL(b);\USLL(a) = USLL(a) ^ USLL(b);}/*用参数type声明类型。*/#define swap4(type,a,b) {type temp;temp=a;a=b;b=temp;}/*用临时内存空间存储。根据不同处理WORD字大小机器而定。32位机sizeof(long double)：12*/#define swap5(a,b) \{ char tempBuf[12];\memcpy(tempBuf,&a,sizeof(a));\memcpy(&a,&b,sizeof(b));\memcpy(&b,tempBuf,sizeof(b)); }/*用模板实现*/template <int N>struct traits //根据字节数得到类型{ typedef void TYPE;};template <>struct traits<sizeof(float)> //模板特化{ typedef unsigned TYPE;};template<>struct traits<sizeof(double)> //模板特化{ typedef unsigned long long TYPE;};template <typename T>typename traits<sizeof(T)>::TYPE &Ref(T &x) //把变量x按另一种类型解释，并返回引用{ return reinterpret_cast<typename traits<sizeof(T)>::TYPE&>(x);}template <typename T>void myswap(T &a, T &b) //类型转换{ Ref(a) = Ref(a) ^ Ref(b); Ref(b) = Ref(a) ^ Ref(b); Ref(a) = Ref(a) ^ Ref(b);}//========================strlen===================================/*递归实现*/int str_len(const char *str){if(*str == '\0') return 0;else return str_len(++str)+1;}/*非递归实现*/char * ToEnd(char * p) { while(*p != '\0') p++; return p; }int mystr_len(char *p) { return ToEnd(p)-p; } int main(){int a = 1;int b = 2;float aa = 1.1;float bb = 2.2;double aaa = -1.11111;double bbb = 2.22222;swap1(a,b); swap2(aa,bb);swap3(aaa,bbb);cout<<a<<" "<<b<<endl;cout<<aa<<" "<<bb<<endl;cout<<aaa<<" "<<bbb<<endl;myswap(a,b);myswap(aa,bb);myswap(aaa,bbb);cout<<a<<" "<<b<<endl;cout<<aa<<" "<<bb<<endl;cout<<aaa<<" "<<bbb<<endl;char *str = "12345";std::cout<<mystr_len(str)<<std::endl;//cout<<"sizeof(long double):"<<sizeof(long double)<<endl;return 0;}
