标签：value bsp bit highlight cout return err inter pre
#include <bits/stdc++.h> using namespace std; char cnt = 0; struct A { A() { *reinterpret_cast<char*>(this) = ++cnt; cout << "construct: " << this << endl; } A(const A &a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(const_cast<A*>(&a)); cout << "copy construct: " << &a << "->" << this << endl; } A(A &&a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(&a); cout << "move construct: " << &a << "->" << this << endl; } A operator=(const A &a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(const_cast<A*>(&a)); cout << "copy assignment: " << &a << "->" << this << endl; return *this; } A operator=(A &&a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(&a); cout << "move assignment: " << &a << "->" << this << endl; return *this; } A get_rvalue() { return *this; } void print() const { cout << "[" << this << "," << (int)*reinterpret_cast<char*>(const_cast<A*>(this))<< "]" << endl; } A& get_lvalue() { return *this; } }; int main() { A a; A &&b = a.get_rvalue(); const A &&c = a.get_rvalue(); // A &d = a.get_rvalue(); // error const A &e = a.get_rvalue(); cout << "-" << endl; a.print(); b.print(); c.print(); e.print(); // A &&f = a; // error // const A &&g = a; // error // A &&h = a.get_lvalue(); // error // const A &&i = a.get_lvalue(); // error A &j = a.get_lvalue(); const A &k = a.get_lvalue(); cout << "--" << endl; j.print(); k.print(); A l; j = l; cout << "---" << endl; l.print(); j.print(); j = b; cout << "----" << endl; b.print(); j.print(); j = c; c.print(); j.print(); return 0; }
输出结果为：
construct: 0x7ffee6778878 copy construct: 0x7ffee6778878->0x7ffee6778868 copy construct: 0x7ffee6778878->0x7ffee6778858 copy construct: 0x7ffee6778878->0x7ffee6778848 - [0x7ffee6778878,1] [0x7ffee6778868,1] [0x7ffee6778858,1] [0x7ffee6778848,1] -- [0x7ffee6778878,1] [0x7ffee6778878,1] construct: 0x7ffee6778830 copy assignment: 0x7ffee6778830->0x7ffee6778878 copy construct: 0x7ffee6778878->0x7ffee6778828 --- [0x7ffee6778830,2] [0x7ffee6778878,2] copy assignment: 0x7ffee6778868->0x7ffee6778878 copy construct: 0x7ffee6778878->0x7ffee6778820 ---- [0x7ffee6778868,1] [0x7ffee6778878,1] copy assignment: 0x7ffee6778858->0x7ffee6778878 copy construct: 0x7ffee6778878->0x7ffee6778818 [0x7ffee6778858,1] [0x7ffee6778878,1]
#include <bits/stdc++.h> using namespace std; char cnt = 0; struct A { A() { *reinterpret_cast<char*>(this) = ++cnt; cout << "construct: " << this << endl; } A(int i) { *reinterpret_cast<char*>(this) = i; cout << "construct(int): " << this << endl; } A(const A &a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(const_cast<A*>(&a)); cout << "copy construct: " << &a << "->" << this << endl; } A(A &&a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(&a); cout << "move construct: " << &a << "->" << this << endl; } A operator=(const A &a) { cout << "enter copy assignment" << endl; *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(const_cast<A*>(&a)); cout << "copy assignment: " << &a << "->" << this << endl; return *this; } A operator=(A &&a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(&a); cout << "move assignment: " << &a << "->" << this << endl; return *this; } A get_rvalue() { return *this; } void print() const { cout << "[" << this << "," << (int)*reinterpret_cast<char*>(const_cast<A*>(this))<< "]" << endl; } A& get_lvalue() { return *this; } ~A() { cout << "destruct: " << this << endl; } }; void test() { A &&a = -1; cout << &a << endl; } void test2() { A &&a = -1; cout << &a << endl; a = -2; cout << &a << endl; } int main() { test();
cout << endl; test2(); return 0; }
输出结果为：
construct(int): 0x7ffee8a8b850 0x7ffee8a8b850 destruct: 0x7ffee8a8b850
construct(int): 0x7ffee8a8b850 0x7ffee8a8b850 construct(int): 0x7ffee8a8b838 move assignment: 0x7ffee8a8b838->0x7ffee8a8b850 copy construct: 0x7ffee8a8b850->0x7ffee8a8b840 destruct: 0x7ffee8a8b840 destruct: 0x7ffee8a8b838 0x7ffee8a8b850 destruct: 0x7ffee8a8b850
拷贝了一次。
#include <bits/stdc++.h> using namespace std; char cnt = 0; struct A { A() { *reinterpret_cast<char*>(this) = ++cnt; cout << "construct: " << this << endl; } A(int i) { *reinterpret_cast<char*>(this) = i; cout << "construct(" << i << "): " << this << endl; } A(const A &a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(const_cast<A*>(&a)); cout << "copy construct("<< (int)*reinterpret_cast<char *>(this) << "): " << &a << "->" << this << endl; } A(A &&a) { *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(&a); cout << "move construct("<< (int)*reinterpret_cast<char *>(this) << "): " << &a << "->" << this << endl; } A operator=(const A &a) { cout << "enter copy assignment" << endl; *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(const_cast<A*>(&a)); cout << "copy assignment("<< (int)*reinterpret_cast<char *>(this) << "): " << &a << "->" << this << endl; return *this; } A operator=(A &&a) { cout << "enter move assignment" << endl; *reinterpret_cast<char *>(this) = *reinterpret_cast<char *>(&a); cout << "move assignment("<< (int)*reinterpret_cast<char *>(this) << "): " << &a << "->" << this << endl; return *this; } A get_rvalue() { return *this; } void print() const { cout << "[" << this << "," << (int)*reinterpret_cast<char*>(const_cast<A*>(this))<< "]" << endl; } A& get_lvalue() { return *this; } ~A() { cout << "destruct: " << this << endl; } }; void test() { A &&a = -1; cout << &a << endl; } void test2() { A &&a = -1; cout << &a << endl; a = -2; cout << &a << endl; } void test3() { A &&a = -1; cout << &a << endl; (a = -2) = -3; cout << &a << endl; } int main() { test3(); return 0; }
输出结果为：
construct(-1): 0x7ffeeef72850 0x7ffeeef72850 construct(-3): 0x7ffeeef72838 construct(-2): 0x7ffeeef72828 enter move assignment move assignment(-2): 0x7ffeeef72828->0x7ffeeef72850 copy construct(-2): 0x7ffeeef72850->0x7ffeeef72830 enter move assignment move assignment(-3): 0x7ffeeef72838->0x7ffeeef72830 copy construct(-3): 0x7ffeeef72830->0x7ffeeef72840 destruct: 0x7ffeeef72840 destruct: 0x7ffeeef72830 destruct: 0x7ffeeef72828 destruct: 0x7ffeeef72838 0x7ffeeef72850 destruct: 0x7ffeeef72850
标签：value bsp bit highlight cout return err inter pre
原文地址：https://www.cnblogs.com/rongminglu/p/12989882.html
