c++拷贝构造函数事例

以下是一个C++拷贝构造函数的例子：

#include <iostream>
#include <cstring>

using namespace std;

class StringBad {
private:
    char *str;
    int len;
    static int num;
public:
    StringBad(const char *s) {
        len = strlen(s);
        str = new char[len + 1];
        strcpy(str, s);
        num++;
        cout << "调用了构造函数" << endl;
    }
    StringBad(const StringBad &st) {
        str = new char[strlen(st.str) + 1];
        strcpy(str, st.str);
        len = st.len;
        num++;
        cout << "调用了拷贝构造函数" << endl;
    }
    ~StringBad() {
        cout << "调用了析构函数" << endl;
        delete [] str;
        num--;
    }
    StringBad & operator=(const StringBad &st) {
        if (this == &st) {
            return *this;
        }
        delete [] str;
        str = new char[strlen(st.str) + 1];
        strcpy(str, st.str);
        len = st.len;
        cout << "调用了赋值运算符" << endl;        return *this;
    }
    friend ostream & operator<<(ostream &os, const StringBad &st) {
        os << st.str;
        return os;
    }
};

int StringBad::num = 0;

int main() {
    StringBad s1("hello");
    StringBad s2(s1);
    StringBad s3 = s1;
    StringBad s4("world");
    s2 = s4;
    cout << s1 << endl;
    cout << s2 << endl;
    cout << s3 << endl;
    cout << s4 << endl;
    cout << "当前对象数量：" << StringBad::num << endl;
    return 0;
}