粗略完成第十五章

practice/booknotes.md

@@ -4454,3 +4454,44 @@ C++提供了几种重用代码的手段。无论使用哪种继 承，基类的
 多重继承（MI）使得能够在类设计中重用多个类的代码。
 
 
+
+# 第十五章 友元、异常和其他
+
+本章内容包括：
+
+- 友元类；
+- 友元类方法；
+- 嵌套类；
+- 引发异常、`try`块和`catch`块；
+- 异常类；
+- 运行阶段类型识别（RTTI）；
+- `dynamic_cast` 和 `typeid`；
+- `static_cast`、`const_cast` 和 `reiterpret_cast`。
+
+
+![image-20210815204948714](https://static.fungenomics.com/images/2021/08/image-20210815204948714.png)
+
+2．bad_alloc异常和new
+
+对于使用new导致的内存分配问题，C++的**最新处理方式是让new引发bad_alloc异常**。头文件new包含bad_alloc类的声明，它是从exception 类公有派生而来的。但**在以前，当无法分配请求的内存量时，new返回 一个空指针**，然后我们可以 `exit(EXIT_FAILURE)`。
+
+
+## 15.6 总结
+
+友元使得能够为类开发更灵活的接口。类可以将其他函数、其他类 和其他类的成员函数作为友元。在某些情况下，可能需要使用前向声 明，需要特别注意类和方法声明的顺序，以正确地组合友元。
+
+嵌套类是在其他类中声明的类，它有助于设计这样的助手类，即实 现其他类，但不必是公有接口的组成部分。
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source/chapter15/constcast.cpp

@@ -0,0 +1,28 @@
+// constcast.cpp -- using const_cast<>
+#include <iostream>
+using std::cout;
+using std::endl;
+
+void change(const int * pt, int n);
+
+int main()
+{
+    int pop1 = 38383;
+    const int pop2 = 2000;
+
+    cout << "pop1, pop2: " << pop1 << ", " << pop2 << endl;
+    change(&pop1, -103);
+    change(&pop2, -103);
+    cout << "pop1, pop2: " << pop1 << ", " << pop2 << endl;
+    // std::cin.get();
+    return 0;
+}
+
+void change(const int * pt, int n)
+{
+    int * pc;
+
+    pc = const_cast<int *>(pt);
+    *pc += n;
+
+}

source/chapter15/error1.cpp

@@ -0,0 +1,30 @@
+//error1.cpp -- using the abort() function
+#include <iostream>
+#include <cstdlib>
+double hmean(double a, double b);
+
+int main()
+{
+    double x, y, z;
+
+    std::cout << "Enter two numbers: ";
+    while (std::cin >> x >> y)
+    {
+        z = hmean(x,y);
+        std::cout << "Harmonic mean of " << x << " and " << y
+            << " is " << z << std::endl;
+        std::cout << "Enter next set of numbers <q to quit>: ";
+    }
+    std::cout << "Bye!\n";
+    return 0;
+}
+
+double hmean(double a, double b)
+{
+    if (a == -b)
+    {
+        std::cout << "untenable arguments to hmean()\n";
+        std::abort();
+    }
+    return 2.0 * a * b / (a + b); 
+}

source/chapter15/error2.cpp

@@ -0,0 +1,38 @@
+//error2.cpp -- returning an error code
+#include <iostream>
+#include <cfloat>  // (or float.h) for DBL_MAX
+
+bool hmean(double a, double b, double * ans);
+
+int main()
+{
+    double x, y, z;
+
+    std::cout << "Enter two numbers: ";
+    while (std::cin >> x >> y)
+    {
+        if (hmean(x,y,&z))
+            std::cout << "Harmonic mean of " << x << " and " << y
+                << " is " << z << std::endl;
+        else
+            std::cout << "One value should not be the negative "
+                << "of the other - try again.\n";
+        std::cout << "Enter next set of numbers <q to quit>: ";
+    }
+    std::cout << "Bye!\n";
+    return 0;
+}
+
+bool hmean(double a, double b, double * ans)
+{
+    if (a == -b)
+    {
+        *ans = DBL_MAX;
+        return false;
+    }
+    else
+    {
+        *ans = 2.0 * a * b / (a + b);
+        return true;
+    }
+}

source/chapter15/error3.cpp

@@ -0,0 +1,34 @@
+// error3.cpp -- using an exception
+#include <iostream>
+double hmean(double a, double b);
+
+int main()
+{
+    double x, y, z;
+
+    std::cout << "Enter two numbers: ";
+    while (std::cin >> x >> y)
+    {
+        try {                   // start of try block
+            z = hmean(x,y);
+        }                       // end of try block
+        catch (const char * s)  // start of exception handler
+        {
+            std::cout << s << std::endl;
+            std::cout << "Enter a new pair of numbers: ";
+            continue;
+        }                       // end of handler
+        std::cout << "Harmonic mean of " << x << " and " << y
+            << " is " << z << std::endl;
+        std::cout << "Enter next set of numbers <q to quit>: ";
+    }
+    std::cout << "Bye!\n";
+    return 0;
+}
+
+double hmean(double a, double b)
+{
+    if (a == -b)
+        throw "bad hmean() arguments: a = -b not allowed";
+    return 2.0 * a * b / (a + b); 
+}

source/chapter15/error4.cpp

@@ -0,0 +1,60 @@
+//error4.cpp – using exception classes
+#include <iostream>
+#include <cmath> // or math.h, unix users may need -lm flag
+#include "exc_mean.h"
+// function prototypes
+double hmean(double a, double b);
+double gmean(double a, double b);
+int main()
+{
+    using std::cout;
+    using std::cin;
+    using std::endl;
+
+    double x, y, z;
+
+    cout << "Enter two numbers: ";
+    while (cin >> x >> y)
+    {
+        try {                  // start of try block
+            z = hmean(x,y);
+            cout << "Harmonic mean of " << x << " and " << y
+                << " is " << z << endl;
+            cout << "Geometric mean of " << x << " and " << y
+                << " is " << gmean(x,y) << endl;
+            cout << "Enter next set of numbers <q to quit>: ";
+        }// end of try block
+        catch (bad_hmean & bg)    // start of catch block
+        {
+            bg.mesg();
+            cout << "Try again.\n";
+            continue;
+        }                  
+        catch (bad_gmean & hg) 
+        {
+            cout << hg.mesg();
+            cout << "Values used: " << hg.v1 << ", " 
+                 << hg.v2 << endl;
+            cout << "Sorry, you don't get to play any more.\n";
+            break;
+        } // end of catch block
+    }
+    cout << "Bye!\n";
+    // cin.get();
+    // cin.get();
+    return 0;
+}
+
+double hmean(double a, double b)
+{
+    if (a == -b)
+        throw bad_hmean(a,b);
+    return 2.0 * a * b / (a + b);
+}
+
+double gmean(double a, double b)
+{
+    if (a < 0 || b < 0)
+        throw bad_gmean(a,b);
+    return std::sqrt(a * b); 
+}

source/chapter15/error5.cpp

@@ -0,0 +1,106 @@
+//error5.cpp -- unwinding the stack
+#include <iostream>
+#include <cmath> // or math.h, unix users may need -lm flag
+#include <string>
+#include "exc_mean.h"
+
+class demo
+{
+private:
+    std::string word;
+public:
+    demo (const std::string & str)
+    {
+
+        word = str;
+        std::cout << "demo " << word << " created\n";
+    }
+    ~demo()
+    {
+        std::cout << "demo " << word << " destroyed\n";
+    }
+    void show() const
+    {
+        std::cout << "demo " << word << " lives!\n";
+    }
+}; 
+
+// function prototypes
+double hmean(double a, double b);
+double gmean(double a, double b);
+double means(double a, double b);
+
+int main()
+{
+    using std::cout;
+    using std::cin;
+    using std::endl;
+
+    double x, y, z;
+	{
+        demo d1("found in block in main()");
+        cout << "Enter two numbers: ";
+        while (cin >> x >> y)
+        {
+               try {                  // start of try block
+                   z = means(x,y);
+                   cout << "The mean mean of " << x << " and " << y
+                           << " is " << z << endl;
+                   cout << "Enter next pair: ";
+               } // end of try block
+               catch (bad_hmean & bg)    // start of catch block
+               {
+                   bg.mesg();
+                   cout << "Try again.\n";
+                   continue;
+               }                  
+               catch (bad_gmean & hg) 
+               {
+                   cout << hg.mesg();
+                   cout << "Values used: " << hg.v1 << ", " 
+                           << hg.v2 << endl;
+                   cout << "Sorry, you don't get to play any more.\n";
+                   break;
+               } // end of catch block
+        }
+        d1.show();
+    }
+    cout << "Bye!\n";
+    // cin.get();
+    // cin.get();
+    return 0;
+}
+
+double hmean(double a, double b)
+{
+    if (a == -b)
+        throw bad_hmean(a,b);
+    return 2.0 * a * b / (a + b);
+}
+
+double gmean(double a, double b)
+{
+    if (a < 0 || b < 0)
+        throw bad_gmean(a,b);
+    return std::sqrt(a * b); 
+}
+
+double means(double a, double b)
+{
+    double am, hm, gm;
+    demo d2("found in means()");
+    am = (a + b) / 2.0;    // arithmetic mean
+    try 
+    {
+        hm = hmean(a,b);
+        gm = gmean(a,b);
+    }
+    catch (bad_hmean & bg) // start of catch block
+    {
+        bg.mesg();
+        std::cout << "Caught in means()\n";
+        throw;             // rethrows the exception 
+    }          
+    d2.show();
+    return (am + hm + gm) / 3.0;
+}

source/chapter15/exc_mean.h

@@ -0,0 +1,32 @@
+// exc_mean.h  -- exception classes for hmean(), gmean()
+#include <iostream>
+
+class bad_hmean
+{
+private:
+    double v1;
+    double v2;
+public:
+    bad_hmean(double a = 0, double b = 0) : v1(a), v2(b){}
+    void mesg();
+};
+
+inline void bad_hmean::mesg()
+{   
+    std::cout << "hmean(" << v1 << ", " << v2 <<"): "
+              << "invalid arguments: a = -b\n";
+}
+
+class bad_gmean
+{
+public:
+    double v1;
+    double v2;
+    bad_gmean(double a = 0, double b = 0) : v1(a), v2(b){}
+    const char * mesg();
+};
+
+inline const char * bad_gmean::mesg()
+{  
+    return "gmean() arguments should be >= 0\n";
+}