C++提高程式設計 4 STL -謂詞
阿新 • • 發佈:2022-03-01
4.2 謂詞
4.2.1 謂詞概念
概念:
返回bool型別的仿函式稱為謂詞(Pred)
返回operator()接受一個引數,那麼叫做一元謂詞
返回operator()接受兩個引數,那麼叫做兩元謂詞
4.2.2 一元謂詞
#include<iostream> using namespace std; #include<algorithm> #include<vector> //仿函式 返回值型別是bool資料型別,稱為謂詞 //一元謂詞 class GreaterFive { public: bool operator()(int val) {return val > 5; } }; void test1() { vector<int>v; for (int i = 0; i < 10; i++) { v.push_back(i); } //查詢容器中有沒有大於5的數字 //GreaterFive() 匿名物件 vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive()); if (it == v.end()) { cout<< "未找到" << endl; } else { cout << "找到了" << endl; //不用再用for迴圈遍歷了 因為此時的it已經是大於5的數字了 直接輸出*it即可 //for (vector<int>::iterator it = v.begin(); it != v.end(); it++) //{ // cout << *it << endl; //}cout << *it << endl; } } int main() { test1(); system("pause"); return 0; }
4.2.2 二元謂詞
#include<iostream> using namespace std; #include<algorithm> #include<vector> //二元謂詞 class myCompare { public: bool operator()(int val1, int val2) { return val1 > val2; } }; void test1() { vector<int>v; v.push_back(10); v.push_back(40); v.push_back(20); v.push_back(30); v.push_back(50); sort(v.begin(), v.end()); for (vector<int>::iterator it = v.begin(); it != v.end(); it++) { cout << *it << " "; // 10 20 30 40 50 } cout << endl; //使用函式物件 改變演算法策略,變為排序規則為從大到小 sort(v.begin(), v.end(), myCompare()); cout << "------------------" << endl; for (vector<int>::iterator it = v.begin(); it != v.end(); it++) { cout << *it << " "; // 50 40 30 20 10 } cout << endl; } int main() { test1(); system("pause"); return 0; }