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unique_ptr的大小探讨

news 2025/7/23 14:34:48

unique_ptr大小和删除器有很大关系，具体区别看如下代码的分析。不要让unique_ptr占用的空间太大，否则不会达到裸指针同样的效果。

#include <iostream>
#include <memory>
using namespace std;class Widget {int m_x;int m_y;int m_z;public:Widget(int x, int y, int z) :m_x(x), m_y(y), m_z(z){}void print() {cout << m_x << "," << m_y << "," << m_z << endl;}~Widget(){cout << "Widget dtor" << endl;}
};struct DeleteWithLog {void operator()(Widget* w) {data++;delete w;cout << "------ DeleteWithLog delete w" << endl;}int data;
};void deleteFunction(Widget* w) {delete w;cout << "------ deleteFunction delete w" << endl;
}int main()
{{unique_ptr<Widget> w1(new Widget(1, 2, 3));w1->print();cout <<"sizeof(w1) = " <<sizeof(w1) << endl;cout << "------ default delete" << endl;}{DeleteWithLog dw;unique_ptr<Widget, DeleteWithLog> w2(new Widget(10, 20, 30));w2->print();cout << "sizeof(w2) = " << sizeof(w2) << endl;}int data1, data2, data3;{auto lambda = [=](Widget * w) {cout << data1 << data2 << data3 << endl;delete w;cout << "------ lambda delete w" << endl;};unique_ptr<Widget, decltype(lambda)> w3(new Widget(100, 200, 300), lambda);w3->print();cout << "sizeof(w3) = " << sizeof(w3) << endl;}{unique_ptr<Widget, void(*)(Widget*)>w4(new Widget(1000, 2000, 3000), deleteFunction);w4->print();cout << "sizeof(w4) = " << sizeof(w4) << endl;}system("pause");
}