谓词是指普通函数或重载的operator()返回值是bool类型的函数对象(仿函数)。如果operator接受一个参数，那么叫做一元谓词,如果接受两个参数，那么叫做二元谓词，谓词可作为一个判断式。
class GreaterThenFive { public: bool operator()(int num) { return num > 5; } }; //一元谓词 void test01() { vector<int> v; for (int i = 0; i < 10;i ++) { v.push_back(i); } vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterThenFive()); if (it == v.end()) { cout << "没有找到" << endl; } else { cout << "找到了: " << *it << endl; } } //二元谓词 class MyCompare { public: bool operator()(int num1, int num2) { return num1 > num2; } }; void test02() { vector<int> v; v.push_back(10); v.push_back(40); v.push_back(20); v.push_back(90); v.push_back(60); //默认从小到大 sort(v.begin(), v.end()); for (vector<int>::iterator it = v.begin(); it != v.end();it++) { cout << *it << " "; } cout << endl; cout << "----------------------------" << endl; //使用函数对象改变算法策略，排序从大到小 sort(v.begin(), v.end(),MyCompare()); for (vector<int>::iterator it = v.begin(); it != v.end(); it++) { cout << *it << " "; } cout << endl; }
