可变长数组的 OO 实现

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
using namespace std;
class CArray {
private:
    int size;
    int *ptr;
public:
    CArray (int s = 0);
    CArray (CArray & a);
    ~CArray ();
    //  必须有的函数 否则就会有莫名的错误。
    void push_back (int v);
    CArray & operator = (const CArray & a);
    int length () {return size;}
    int & operator [] (int i) {return ptr[i];}
    void print ();
};

CArray :: CArray(int s): size(s){
    if (s == 0) {
        ptr = NULL;
    }
    else {
        ptr = new int [s];
    }
}

CArray :: CArray (CArray & a) {
    if (!a.ptr) {
        ptr = NULL;
        size = 0;
        return ;
    }
    size = a.length();
    ptr = new int[size];
    for (int i = 0;i < size; ++ i) {
        ptr[i] = a[i];
    }
}

CArray :: ~CArray () {
    if (size) {
        delete []ptr;
    }
}

CArray & CArray :: operator = (const CArray & a) {
    if (ptr == a.ptr) {
        return *this;
    }
    if (a.ptr == NULL) {
        if (ptr) {
            delete []ptr;
            ptr = NULL;
            size = 0;
            return *this;
        }
    }
    size = a.size;
    delete []ptr;
    ptr = new int[size];
    for (int i = 0;i < size; ++ i) ptr[i] = a.ptr[i];
    return *this;
}

void CArray:: push_back(int v) {
    if (ptr) {
        int * temp = new int[size + 1];
        memcpy (temp,ptr,size * (sizeof (int)));
        delete [] ptr;
        ptr = temp;
    }
    else {
        ptr = new int[1];
    }
    ptr[size ++] = v;
}

void CArray:: print () {
    for (int i = 0;i < size; ++ i) {
        cout << ptr[i] << ' ';
    }
    cout << endl;
}

int main () {
    ios_base :: sync_with_stdio(false);
    CArray a(0);
    for (int i = 0;i < 5; ++ i) {
        a.push_back (i);
    }
    CArray a2(0),a3(0);
    a2 = a;
    a2.print();
    a2 = a3;
    a2.print();
    a[3] = 100;
    CArray a4(a);
    a4.print ();
    return 0;
}