STD矢量C ++ - 深或浅的拷贝(std vector C++

我不知道是否复制载体，我与它的值复制向量（而这是不具有阵列工作，并深拷贝需要一个循环或memcpy的）。

你可以暗示解释？

问候

Answer 1:

你是一个深拷贝复制的向量的任何时间。但是，如果你的载体是你所得到的指针的副本指针的载体，而不是值指出，

例如：

std::vector<Foo> f;
std::vector<Foo> cp = f; //deep copy. All Foo copied

std::vector<Foo*> f;
std::vector<Foo*> cp = f; //deep copy (of pointers), or shallow copy (of objects).
//All pointers to Foo are copied, but not Foo themselves

Answer 2:

矢量将调整到有物体足够的空间。然后，它会通过对象迭代，并调用默认的拷贝操作为每个对象。

通过这种方式，载体的副本是“深”。向量中的每个对象的副本无论是用于默认复印操作员定义。

在示例中......这是不好的代码：

#include <iostream>
#include <vector>

using namespace std;

class my_array{
public:
    int *array;
    int size;
    my_array(int size, int init_val):size(size){
        array = new int[size];
        for(int i=0; i<size; ++i)
            array[i]=init_val;
    }
    ~my_array(){
        cout<<"Destructed "<<array[0]<<endl;
        if(array != NULL)
            delete []array;
        array = NULL;
        size = 0;
    }

};

void add_to(vector<my_array> &container){
    container.push_back(my_array(4,1));
}

int main(){

    vector<my_array> c;
    {
        my_array a(5,0);
        c.push_back(a);
    }
    add_to(c);
    //At this point the destructor of c[0] and c[1] has been called.
    //However vector still holds their 'remains'
    cout<<c[0].size<<endl; //should be fine, as it copies over with the = operator
    cout<<c[0].array[0]<<endl;//undefined behavior, the pointer will get copied, but the data is not valid
    return 0;
}

这是更好的代码：

#include <iostream>
#include <vector>

using namespace std;

class my_array{
public:
    int *array;
    int size;
    my_array(int size, int init_val):size(size){
        cout<<"contsructed "<<init_val<<endl;
        array = new int[size];
        for(int i=0; i<size; ++i)
            array[i]=init_val;
    }
    my_array(const my_array &to_copy){
        cout<<"deep copied "<<to_copy.array[0]<<endl;
        array = new int[to_copy.size];
        size = to_copy.size;
        for(int i=0; i<to_copy.size; i++)
            array[i]=to_copy.array[i];
    }

    ~my_array(){
        cout<<"Destructed "<<array[0]<<endl;
        if(array != NULL)
            delete []array;
        array = NULL;
        size = 0;
    }

};

void add_to(vector<my_array> &container){
    container.push_back(my_array(4,1));
}

int main(){

    vector<my_array> c;
    {
        my_array a(5,0);
        c.push_back(a);
    }
    add_to(c);
    //At this point the destructor of c[0] and c[1] has been called.
    //However vector holds a deep copy'
    cout<<c[0].size<<endl; //This is FINE
    cout<<c[0].array[0]<<endl;//This is FINE
    return 0;
}