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fa9377e4ae
- 新增现代 C++ 教程的 Preface 章节，包括英文和中文版本 - 添加 C++ Primer 练习代码 - 新增 Learn C++ 教程的 C++ 开发简介章节 - 添加头文件解析文档 - 更新 mkdocs.yml，包含新教程的目录结构 - 修改项目设置，使用 Python 3.10环境
129 lines
2.1 KiB
Markdown
129 lines
2.1 KiB
Markdown
# C++的谓词
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# 1. 简介
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① 返回bool类型的仿函数称为谓词。
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② 如果operator()接受一个参数，那么叫做一元谓词。
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③ 如果operator()接受两个参数，那么叫做二元谓词。
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# 2. 一元谓词
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```python
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#include<iostream>
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using namespace std;
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#include<vector>
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#include<algorithm>
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//仿函数 返回值类型是bool数据类型，称为谓词
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//一元谓词
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class GreaterFive
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{
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public:
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bool operator()(int val)
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{
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return val > 5;
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}
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};
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void test01()
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{
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vector<int>v;
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for (int i = 0; i < 10; i++)
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{
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v.push_back(i);
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}
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//查找容器中，有没有大于5的数字
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//GreaterFive() 匿名函数对象
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vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive());
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if (it == v.end())
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{
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cout << "未找到" << endl;
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}
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else
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{
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cout << "找到大于5的数字为：" << *it << endl;
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}
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}
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int main()
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{
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test01();
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system("pause");
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return 0;
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}
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```
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运行结果：
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- 找到大于5的数字为：6
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- 请按任意键继续. . .
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# 3. 二元谓词
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```python
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#include<iostream>
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using namespace std;
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#include<vector>
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#include<algorithm>
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//仿函数 返回值类型是bool数据类型，称为谓词
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//二元谓词
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class MyCompare
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{
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public:
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bool operator()(int val1,int val2)
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{
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return val1 > val2;
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}
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};
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void test01()
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{
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vector<int>v;
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v.push_back(10);
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v.push_back(40);
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v.push_back(50);
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v.push_back(20);
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v.push_back(30);
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sort(v.begin(), v.end());
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for (vector<int>::iterator it = v.begin(); it != v.end(); it++)
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{
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cout << *it << " ";
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}
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cout << endl;
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//使用函数对象，改变算法策略，变为排序规则为从大到小
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sort(v.begin(), v.end(), MyCompare()); //MyCompare()为函数对象，是匿名函数
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cout << "----" << endl;
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for (vector<int>::iterator it = v.begin(); it != v.end(); it++)
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{
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cout << *it << " ";
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}
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cout << endl;
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}
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int main() {
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test01();
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system("pause");
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return 0;
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}
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```
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运行结果：
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- 10 20 30 40 50
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- $----$
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- 50 40 30 20 10
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- 请按任意键继续. . .
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