C++ Primer Plus 学习笔记第十四章 valarray类私有继承

我不是女神ヾ 2022-04-25 10:24 240阅读 0赞

Valarray类

模板类

格式：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70][]

基本函数：

![20190531133342880.png][]

![2019053114232643.png][]

![20190531142332947.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70 1][]

程序示例：

studentc.h 奇怪 为毛没有彩色

#ifndef STUDENTC_H_
    #define STUDENTC_H_
    
    #include <iostream>
    #include <string>
    #include <valarray>
    class Student
    {
      private:
        typedef std::valarray<double> ArrayDb;
        std::string name;
        ArrayDb scores;
        std::ostream & arr_out(std::ostream & os) const;
      public:
        Student() : name("Null Student"), scores() {}
        explicit Student(const std::string & s) : name(s), scores() {}
        explicit Student(int n) : name("Nully"), scores(n) {}
        Student(const std::string & s, int n) : name(s), scores(n) {}
        Student(const std::string & s, const ArrayDb & a) : name(s), scores(a) {}
        Student(const char* str, const double* pd, int n) : name(str), scores(pd, n) {}
        ~Student() {}
        double Average() const;
        const std::string & Name() const;
        double & operator[] (int i);
        double operator[] (int i) const;
    
        friend std::istream & operator >> (std::istream & is, Student & stu);
        friend std::istream & getline(std::istream & is, Student & stu);
        friend std::ostream & operator << (std::ostream & os, const Student & stu);
    };
    
    #endif

student.cpp

#include "studentc.h"
    using std::ostream;
    using std::endl;
    using std::istream;
    using std::string;
    
    double Student::Average() const
    {
      if (scores.size() > 0)
        return scores.sum() / scores.size();
      else
        return 0;
    }
    
    const string & Student::Name() const
    {
      return name;
    }
    
    double & Student::operator[](int i)
    {
      return scores[i];
    }
    
    double Student::operator[](int i) const
    {
      return scores[i];
    }
    
    ostream & Student::arr_out(ostream & os) const
    {
      int i;
      int lim = scores.size();
      if (lim > 0)
      {
        for (i = 0; i < lim; i++)
        {
          os << scores[i] << " ";
          if (i % 5 == 4)
            os <<endl;
        }
        if (i % 5 != 0)
          os << endl;
      }
      else
        os << "empty array ";
      return os;
    }
    
    istream & operator >>(istream & is, Student & stu)
    {
      is >> stu.name;
      return is;
    }
    istream & getline(istream & is, Student & stu)
    {
      getline(is, stu.name);
      return is;
    }
    
    ostream & operator<<(ostream & os, const Student & stu)
    {
      os << "Scores for " << stu.name << ":\n";
      stu.arr_out(os);
      return os;
    }

use\_stuc.cpp

#include <iostream>
    #include "studentc.h"
    using std::cout;
    using std::cin;
    using std::endl;
    
    
    void set(Student & sa, int n);
    const int pupils = 3;
    const int quizzes = 5;
    
    int main()
    {
      Student ada[pupils] =
        {Student(quizzes), Student(quizzes), Student(quizzes)};
    
      int i;
      for (i = 0; i < pupils; ++i)
        set(ada[i], quizzes);
      cout << "\nResults:";
      for ( i = 0; i < pupils; ++i)
      {
        cout << endl << ada[i];
        cout << "average: " << ada[i].Average() <<endl;
      }
      cout << "Done.\n";
      return 0;
    }
    
    void set(Student & sa, int n)
    {
      cout << "Please enter the student's name: ";
      getline(cin, sa);
      cout << "Please enter " << n << "quiz scores:\n";
      for ( int i = 0; i <n; i++)
        cin >> sa[i];
      while (cin.get() != '\n')
        continue;
    }

运行结果

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70 2][]

私有继承：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70 3][]

私有继承与包含的区别：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70 4][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70 5][]

如果需要调用基类的对象咋搞？

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70 6][]

在私有继承中，在没有显式类型转换的情况下，不能将指向派生类的对象或引用赋给基类引用或指针

还有一种情况是 多重继承 编译器无法确定要转换成哪个基类 因为都有operator<<()

私有继承的程序示例：

studenti.h

#ifndef STUDENTC_H_
    #define STUDENTC_H_
    
    #include <iostream>
    #include <string>
    #include <valarray>
    class Student : private std::string, private std::valarray<double>
    {
      private:
        typedef std::valarray<double> ArrayDb;
        std::ostream & arr_out(std::ostream & os) const;
      public:
        Student() : std::string("Null Student"), ArrayDb() {}
        explicit Student(const std::string & s) : std::string(s), ArrayDb() {}
        explicit Student(int n) : std::string("Nully"), ArrayDb(n) {}
        Student(const std::string & s, int n) : std::string(s), ArrayDb(n) {}
        Student(const std::string & s, const ArrayDb & a) : std::string(s), ArrayDb(a) {}
        Student(const char* str, const double* pd, int n) : std::string(str), ArrayDb(pd, n) {}
        ~Student() {}
        double Average() const;
        const std::string & Name() const;
        double & operator[] (int i);
        double operator[] (int i) const;
    
        friend std::istream & operator >> (std::istream & is, Student & stu);
        friend std::istream & getline(std::istream & is, Student & stu);
        friend std::ostream & operator << (std::ostream & os, const Student & stu);
    };
    
    #endif

studenti.cpp

#include "studenti.h"
    using std::ostream;
    using std::endl;
    using std::istream;
    using std::string;
    
    double Student::Average() const
    {
      if (ArrayDb::size() > 0)
        return ArrayDb::sum() / ArrayDb::size();
      else
        return 0;
    }
    
    const string & Student::Name() const
    {
      return (const string &) *this;
    }
    
    double & Student::operator[](int i)
    {
      return ArrayDb::operator[](i);
    }
    
    double Student::operator[](int i) const
    {
      return ArrayDb::operator[](i);
    }
    
    ostream & Student::arr_out(ostream & os) const
    {
      int i;
      int lim = ArrayDb::size();
      if (lim > 0)
      {
        for (i = 0; i < lim; i++)
        {
          os << ArrayDb::operator[](i) << " ";
          if (i % 5 == 4)
            os <<endl;
        }
        if (i % 5 != 0)
          os << endl;
      }
      else
        os << "empty array ";
      return os;
    }
    
    istream & operator >>(istream & is, Student & stu)
    {
      is >> (string &) stu;
      return is;
    }
    istream & getline(istream & is, Student & stu)
    {
      getline(is, (string &) stu);
      return is;
    }
    
    ostream & operator<<(ostream & os, const Student & stu)
    {
      os << "Scores for " << (string &) stu << ":\n";
      stu.arr_out(os);
      return os;
    }

use\_stui.cpp

#include <iostream>
    #include "studenti.h"
    using std::cout;
    using std::cin;
    using std::endl;
    
    
    void set(Student & sa, int n);
    const int pupils = 3;
    const int quizzes = 5;
    
    int main()
    {
      Student ada[pupils] =
        {Student(quizzes), Student(quizzes), Student(quizzes)};
    
      int i;
      for (i = 0; i < pupils; ++i)
        set(ada[i], quizzes);
      cout << "\nResults:";
      for ( i = 0; i < pupils; ++i)
      {
        cout << endl << ada[i];
        cout << "average: " << ada[i].Average() <<endl;
      }
      cout << "Done.\n";
      return 0;
    }
    
    void set(Student & sa, int n)
    {
      cout << "Please enter the student's name: ";
      getline(cin, sa);
      cout << "Please enter " << n << "quiz scores:\n";
      for ( int i = 0; i <n; i++)
        cin >> sa[i];
      while (cin.get() != '\n')
        continue;
    }

用包含还是用私有继承？

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70 7][]

完结

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[20190531133342880.png]: /images/20220125/0018fb47b53547168077b05cb6d4887b.png
[2019053114232643.png]: /images/20220125/810860789a99459db33241774682c1ba.png
[20190531142332947.png]: /images/20220125/026ec30a47e1418b98ecffe1ec92464f.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvdWx3eWI_size_16_color_FFFFFF_t_70 2]: /images/20220125/d92c4348a72b45f98b194e8dce652533.png
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