场景:
1. 算法库的函数参数大部分都定义了一个回调, 用来作为比较判断,排序等,比如replace_if 和 sort.
2. 大部分算法库里的函数基本都需要数据结构是已排序的.
3. 使用某个函数时,如何快速写出比较函数(类型)很重要,因为快速写出比较类型可以省很多时间.比如UnaryPredicate 和BinaryPredicate类型.
参考:
需要注意的是: strict weak ordering 顺序需要遵守以下规则:
Establishes strict weak ordering relation with the following propertiesFor all a, comp(a,a)==falseIf comp(a,b)==true then comp(b,a)==falseif comp(a,b)==true and comp(b,c)==true then comp(a,c)==truetest.cpp// test.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <algorithm>#include <math.h>#include <ctype.h>#include <assert.h>#include <Windows.h>#include <string>#include <iostream>#include <vector>//UnaryPredicate 一元比较//template <typename T>//struct MyUnaryPredicate//{//bool operator()(const T& t)//{//if(isdigit((unsigned char)t))//{//return true;//}//return false;//}//};// 除了以上声明类之外,也可以使用函数,C++函数也是一种模板类型template <typename T>static bool MyUnaryPredicate(const T& t){if(isdigit((unsigned char)t)){return true;}return false;}void TestMyUnaryPredicate(){std::cout << "======TestMyUnaryPredicate=================" << std::endl;std::string str("hsdfasd1asdfas2sadfas3");//MyUnaryPredicate<char> pre;std::replace_if(str.begin(),str.end(),MyUnaryPredicate<char>,’#’);std::cout << str << std::endl;std::wstring wstr(L"hsdfasd1asdfas2sadfas3");//MyUnaryPredicate<wchar_t> wpre;std::replace_if(wstr.begin(),wstr.end(),MyUnaryPredicate<wchar_t>,L’#’);std::wcout << wstr << std::endl;}//BinaryPredicate, 二元比较//template <typename T>//struct MyBinaryPredicate//{//bool operator()(const T& val1,const T& val2)//{//if(val1 < val2)//{//return true;//}//return false;//}//};template <typename T>bool MyBinaryPredicate(const T& val1,const T& val2){if(val1 < val2){return true;}return false;}void TestMyBinaryPredicate(){std::string str("asaisyfoasvzxlpqwobri");//MyBinaryPredicate<char> up;std::sort(str.begin(),str.end(),MyBinaryPredicate<char>);std::cout << "======TestMyBinaryPredicate=================" << std::endl;std::cout << str << std::endl;}template <typename T>bool MatchInvalidCharPredicate(const T& t){unsigned char t1 = (unsigned char)t;if(t1 <= 0x1F || t1 == 0x7F || t1 == 0x5C|| t1 == 0x2F|| t1 == 0x3A|| t1 == 0x2A|| t1 == 0x3F|| t1 == 0x22|| t1 == 0x3C|| t1 == 0x7C){return true;}return false;}template<typename C,class T> void FilterInvalidFileNameChar(T& c){std::replace_if(c.begin(),c.end(),MatchInvalidCharPredicate<C>,L’_’);}inline char* Unicode2Ansi(const wchar_t* unicode){int len;len = WideCharToMultiByte(CP_ACP, 0, unicode, -1, NULL, 0, NULL, NULL);char *szUtf8 = (char*)malloc(len + 1);memset(szUtf8, 0, len + 1);WideCharToMultiByte(CP_ACP, 0,unicode, -1, szUtf8, len, NULL,NULL);return szUtf8;} void TestFilterInvalidFileNameChar(){std::wstring wss(L"/as中国fasdfas?asdfas*dfa.txt");FilterInvalidFileNameChar<wchar_t>(wss);std::cout << "======TestFilterInvalidFileNameChar=================" << std::endl;std::wcout << Unicode2Ansi(wss.c_str()) << std::endl;}int _tmain(int argc, _TCHAR* argv[]){TestMyUnaryPredicate();TestMyBinaryPredicate();TestFilterInvalidFileNameChar();system("pause");return 0;}
输出:
======TestMyUnaryPredicate=================hsdfasd#asdfas#sadfas#hsdfasd#asdfas#sadfas#======TestMyBinaryPredicate=================aaabfiiloopqrsssvwxyz======TestFilterInvalidFileNameChar=================_as中国fasdfas_asdfas_dfa.txt
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