Predicate concept
concept:
A functor that returns a bool type is called a predicate
If operator() accepts a parameter, it is called a unary predicate
If operator() accepts two parameters, it is called a binary predicate
Unary predicate
Code example:
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
//仿函数 返回值类型是bool数据类型，称为谓词
//一元谓词
class GreaterFive
{
public:
bool operator()(int val)
{
return val > 5;
}
};
void test01()
{
vector<int>v;
for (int i = 0; i < 10; i++)
{
v.push_back(i);
}
//查找容器中 有没有大于5的数字
//GreaterFive（）匿名函数对象
vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive());
if (it == v.end())
{
cout << "未找到" << endl;
}
else
{
cout << "找到了大于5的数字为：" << *it << endl;
}
}
int main()
{
test01();
system("pause");
return 0;
}
Summary: The parameter has only one predicate, called a unary predicate
Example of binary predicate code:
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
//二元谓词
class MyCompare
{
public:
bool operator()(int val1, int val2)
{
return val1 > val2;
}
};
void test01()
{
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 << " ";
}
cout << endl;
//使用函数对象，改变算法策略，变为排序规则为从大到小
sort(v.begin(), v.end(), MyCompare());
cout << "-----------------------------" << endl;
for (vector<int>::iterator it = v.begin(); it != v.end(); it++)
{
cout << *it << " ";
}
cout << endl;
}
int main()
{
test01();
system("pause");
return 0;
}
Summary: A predicate with only two parameters is called a binary predicate