函數(shù)對(duì)象
c++中函數(shù)名后的()稱為函數(shù)調(diào)用運(yùn)算符。函數(shù)調(diào)用運(yùn)算符也可以重載，如果某個(gè)類重載了函數(shù)調(diào)用運(yùn)算符，則該類的實(shí)例就是一個(gè)函數(shù)對(duì)象。函數(shù)對(duì)象本身并不是很有用，但他們使得算法操作的參數(shù)化策略成為可能，使通用性算法變得更加通用(讓函數(shù)作為參數(shù)還可以通過函數(shù)指針)實(shí)例
class Add{ double Operator()(double x,double y) { return x+y; }};Add plus; //plus就是一個(gè)函數(shù)對(duì)象cout<<plus(1.2,3.4)<<endl;//通過函數(shù)對(duì)象調(diào)用重載函數(shù)cout<<Add() ()(1.2,3.4)<<endl; //Add()會(huì)創(chuàng)建一個(gè)臨時(shí)對(duì)象學(xué)習(xí)代碼
#include <iostream>#include <vector>#include <list>#include <algorithm>using namespace std;/*class absInt {};*/ //class和struct都是定義類，struct成員默認(rèn)屬性為publicvoid PRint(double i){ cout << i << " ";}void myforeach(vector<double>::iterator & t1, vector<double>::iterator & t2, void(*fun)(double i))//可以通過函數(shù)指針將一個(gè)函數(shù)作為另一個(gè)函數(shù)的參數(shù){ while (t1 != t2) { fun(*t1); ++t1; }}struct absInt { //重載操作符() int operator()(int val) { return val < 0 ? -val : val; }};template <typename elementType>void FuncDisplayElement(const elementType & element){ cout << element << " " ;}template <typename elementType>struct DisplayElement { //存儲(chǔ)狀態(tài) int m_nCount; DisplayElement() { m_nCount = 0; } void operator()(const elementType & element) { ++m_nCount; cout << element << " "; }};int main(){ absInt absObj;//函數(shù)對(duì)象 int i = -2; unsigned int ui = absObj(i);//通過函數(shù)對(duì)象調(diào)用函數(shù) cout << ui << endl; vector<int> a; for (int i = 0; i < 10; i++) { a.push_back(i); } DisplayElement<int> mResult; mResult = for_each(a.begin(), a.end(), mResult);//把函數(shù)對(duì)象作為參數(shù)傳遞給另一個(gè)函數(shù) cout << endl; cout << "數(shù)量" << mResult.m_nCount << endl; list<char> b; for (char c = 'a'; c < 'k'; ++c) { b.push_back(c); } for_each(b.begin(), b.end(), DisplayElement<char>());//DisplayElement<char>()會(huì)創(chuàng)建一個(gè)臨時(shí)對(duì)象 cout << endl; vector<double> vec = { 76,92,86,74,95 }; cout << "vec里的類容為:" << endl; for_each(vec.begin(), vec.end(), print); cout << "vec里的內(nèi)容為" << endl; myforeach(vec.begin(), vec.end(), print); getchar(); return 0;}新聞熱點(diǎn)
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