new对象和delete

base/new/placenew.cpp

@@ -0,0 +1,67 @@
+//
+// Created by zhuyijun on 2021/8/20.
+//
+
+#include <iostream>
+#include <string>
+#include <new>
+
+using namespace std;
+const int BUF = 512;
+
+class JustTesting {
+private:
+    string words;
+    int number;
+public:
+    JustTesting(const string &s = "JustTesting", int n = 0) {
+        words = s;
+        number = n;
+        cout << words << " constructed" << endl;
+    }
+
+    ~JustTesting() {
+        cout << words << " destroyed" << endl;
+    }
+
+    void Show() const {
+        cout << words << ", " << number << endl;
+    }
+};
+
+int main() {
+    char *buffer = new char[BUF];
+    JustTesting *pc1, *pc2;
+    pc1 = new(buffer)JustTesting;
+    pc2 = new JustTesting("Heap1", 20);
+
+    cout << "Memory block addresses:\n" << "buffer: " << (void *) buffer << " heap: " << pc2 << endl;
+    cout << "Memory contents: \n";
+    cout << pc1 << ": ";
+    pc1->Show();
+    cout << pc2 << ": ";
+    pc2->Show();
+
+    JustTesting *pc3, *pc4;
+//    pc3 = new(buffer)JustTesting("Bad Idea",6);
+    pc3 = new(buffer + sizeof(JustTesting))JustTesting("Bad Idea", 6);
+    pc4 = new JustTesting("Heap2", 10);
+
+    cout << "Memory contents: \n";
+    cout << pc3 << ": ";
+    pc3->Show();
+    cout << pc4 << ": ";
+    pc4->Show();
+
+    //free Heap1
+    delete pc2;
+    //free Heap2
+    delete pc4;
+    //调用析构函数
+    pc3->~JustTesting();
+    pc1->~JustTesting();
+    //free buffer
+    delete[] buffer;
+    cout << "Dome\n";
+    return 0;
+}

base/new/saystring.cpp

@@ -0,0 +1,54 @@
+//
+// Created by zhuyijun on 2021/8/20.
+//
+
+
+#include "string.h"
+
+const int ArSize = 10;
+const int MaxLen = 81;
+
+int main() {
+
+    using std::cout;
+    using std::cin;
+    using std::endl;
+    String name;
+    cout << "Hi, what's your name?\n>> ";
+    cin >> name;
+    cout << name << ", Please enter up to " << ArSize << "shart sayings < empty line to quit:" << endl;
+    String sayings[ArSize];
+    char temp[MaxLen];
+    int i;
+    for (i = 0; i < ArSize; ++i) {
+        cout << i + 1 << ": ";
+        cin.get(temp, MaxLen);
+        while (cin && cin.get() != '\n')
+            continue;
+        if (!cin || temp[0] == '\0')
+            break;
+        else
+            sayings[i] = temp;
+    }
+    int total = i;
+    if (total > 0) {
+        cout << "Here are your sayings: \n";
+        for (i = 0; i < total; ++i) {
+            cout << sayings[i][0] << ": " << sayings[i] << endl;
+        }
+        int shortest = 0;
+        int first = 0;
+        for (i = 1; i < total; ++i) {
+            if (sayings[i].length() < sayings[shortest].length())
+                shortest = i;
+            if (sayings[i] < sayings[first])
+                first = i;
+        }
+        cout << "Shortest saying:\n" << sayings[shortest] << endl;
+        cout << "First alphabetically: \n" << sayings[first] << endl;
+        cout << "This program used " << String::HowMany() << " String object. Bye. " << endl;
+    } else
+        cout << "No input ! Bye." << endl;
+    return 0;
+}
+

base/new/string.cpp

@@ -0,0 +1,86 @@
+//
+// Created by zhuyijun on 2021/8/20.
+//
+
+#include <cstring>
+#include "string.h"
+
+using std::cin;
+using std::cout;
+using std::endl;
+int String::num_strings = 0;
+
+int String::HowMany() {
+    return num_strings;
+}
+
+String::String() {
+    len = 4;
+    str = new char[1];
+    str[0] = '\0';
+    num_strings++;
+}
+
+String::String(const char *s) {
+    len = std::strlen(s);
+    str = new char[len + 1];
+    std::strcpy(str, s);
+    num_strings++;
+}
+
+String::~String() {
+    --num_strings;
+    delete[] str;
+}
+
+String &String::operator=(const String &st) {
+    if (this == &st) {
+        return *this;
+    }
+    delete[] str;
+    len = st.len;
+    str = new char[len + 1];
+    std::strcpy(str, st.str);
+    return *this;
+}
+
+String &String::operator=(const char *s) {
+    delete[] str;
+    len = std::strlen(s);
+    str = new char[len + 1];
+    std::strcpy(str, s);
+    return *this;
+}
+
+char &String::operator[](int i) {
+    return str[i];
+}
+
+const char &String::operator[](int i) const {
+    return str[i];
+}
+
+bool operator<(const String &st, const String &st2) {
+    return (std::strcmp(st.str, st2.str) < 0);
+}
+
+bool operator>(const String &st1, const String &st2) {
+    return (std::strcmp(st1.str, st2.str) < 0);
+}
+
+bool operator==(const String &st, const String &st2) {
+    return (std::strcmp(st.str, st2.str) == 0);
+}
+
+std::ostream &operator<<(std::ostream &os, const String &st) {
+    os << st.str;
+    return os;
+}
+
+std::istream &operator>>(std::istream &is, String &st) {
+    char temp[String::CINLIM];
+    is.get(temp, String::CINLIM);
+    if (is) st = temp;
+    while (is && is.get() != '\n') continue;
+    return is;
+}

base/new/string.h

@@ -0,0 +1,57 @@
+//
+// Created by zhuyijun on 2021/8/20.
+//
+
+#ifndef BASE_STRING_H
+#define BASE_STRING_H
+
+#include <iostream>
+
+using std::ostream;
+using std::istream;
+
+class String {
+private:
+    char *str;
+    int len;
+    static int num_strings;
+    static const int CINLIM = 80;
+public:
+    String(const char *s);
+
+    String();
+
+    String(const String &);
+
+    ~String();
+
+    int length() const {
+        return len;
+    }
+
+    //运算符重载
+    String &operator=(const String &);
+
+    String &operator=(const char *);
+
+    char &operator[](int i);
+
+    const char &operator[](int i) const;
+
+    //友元
+    friend bool operator<(const String &st, const String &st2);
+
+    friend bool operator>(const String &st1, const String &st2);
+
+    friend bool operator==(const String &st, const String &st2);
+
+    friend ostream &operator<<(ostream &os, const String &st);
+
+    friend istream &operator>>(istream &is, String &st);
+
+    //静态函数
+    static int HowMany();
+};
+
+
+#endif //BASE_STRING_H

base/new/stringbad.cpp

@@ -33,6 +33,17 @@ StringBad::~StringBad() {
     delete[] str;
 }
 
+StringBad &StringBad::operator=(const StringBad &st) {
+    if (this == &st) {
+        return *this;
+    }
+    delete[] str;
+    len = st.len;
+    str = new char[len + 1];
+    std::strcpy(str, st.str);
+    return *this;
+}
+
 std::ostream &operator<<(std::ostream &os, const StringBad &st) {
     os << st.str;
     return os;

base/new/stringbad.h

@@ -4,19 +4,26 @@
 
 #ifndef BASE_STRINGBAD_H
 #define BASE_STRINGBAD_H
+
 #include <iostream>
 
 class StringBad {
 
 private:
-    char * str;
+    char *str;
     int len;
     static int num_strings;
 public:
-    StringBad(const char * s);
+    StringBad(const char *s);
+
     StringBad();
+
     ~StringBad();
-    friend std::ostream & operator<<(std::ostream & os,const StringBad & st);
+
+    StringBad &operator=(const StringBad &);
+
+    friend std::ostream &operator<<(std::ostream &os, const StringBad &st);
+
 };