strlen()和swap() 兩個函數的實現（特定條件下）。

/**************************@author: weedge@date: 21/07/2011@comment:1.不用局部變數和全域變數實現strlen；參考http://www.cppblog.com/ant/archive/2007/10/12/32886.html2.有2資料，寫一個交換資料的宏 *******************************************/ #include <iostream>using namespace std;//========================swap===================================/*不能處理浮點數*/#define swap1(a,b) {a=a^b;b=a^b;a=a^b;}/*會出現溢出情況*/#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;}/*單精確度浮點數情況*/#define US(x) (*(unsigned*)(&x)) //按無符號數讀取x所在記憶體單元。#define swap2(a,b) {US(a) = US(a) ^ US(b); US(b) = US(a) ^ US(b); US(a) = US(a) ^ US(b);}/*雙精確度浮點數情況。*/#define USLL(x) (*(unsigned long long*)(&x)) //按64位無符號數讀取x所在記憶體單元。#define swap3(a,b)\ { USLL(a) = USLL(a) ^ USLL(b);\USLL(b) = USLL(a) ^ USLL(b);\USLL(a) = USLL(a) ^ USLL(b);}/*用參數type宣告類型。*/#define swap4(type,a,b) {type temp;temp=a;a=b;b=temp;}/*用臨時記憶體空間儲存。根據不同處理WORD字大小機器而定。32位機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)); }/*用模板實現*/template <int N>struct traits                        //根據位元組數得到類型{    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)           //把變數x按另一種類型解釋，並返回引用{    return  reinterpret_cast<typename traits<sizeof(T)>::TYPE&>(x);}template <typename T>void myswap(T &a, T &b)                              //類型轉換{      Ref(a) = Ref(a) ^ Ref(b);      Ref(b) = Ref(a) ^ Ref(b);      Ref(a) = Ref(a) ^ Ref(b);}//========================strlen===================================/*遞迴實現*/int str_len(const char *str){if(*str == '\0') return 0;else return str_len(++str)+1;}/*非遞迴實現*/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;}