[C/C++标准库]_[初级]_[使用算法库函数时需要注意自定义BinaryPredicate和UnaryPredicate]

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:

http://en.cppreference.com/w/cpp/algorithm/replace

http://en.cppreference.com/w/cpp/algorithm/sort

http://en.cppreference.com/w/cpp/concept/Compare

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 properties
For all a, comp(a,a)==false
If comp(a,b)==true then comp(b,a)==false
if comp(a,b)==true and comp(b,c)==true then comp(a,c)==true

test.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