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update: more explaination on move proposal

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Changkun Ou
2019-06-05 14:11:55 +02:00
parent 07badc85f7
commit 5c37806f62
2 changed files with 33 additions and 14 deletions
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22
book/zh-cn/03-runtime.md
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@@ -267,16 +267,26 @@ int main()
class A {
public:
int *pointer;
A():pointer(new int(1)) { std::cout << "构造" << pointer << std::endl; }
A(A& a):pointer(new int(*a.pointer)) { std::cout << "拷贝" << pointer << std::endl; } // 无意义的对象拷贝
A(A&& a):pointer(a.pointer) { a.pointer = nullptr;std::cout << "移动" << pointer << std::endl; }
~A(){ std::cout << "析构" << pointer << std::endl; delete pointer; }
A():pointer(new int(1)) {
std::cout << "构造" << pointer << std::endl;
}
A(A& a):pointer(new int(*a.pointer)) {
std::cout << "拷贝" << pointer << std::endl;
} // 无意义的对象拷贝
A(A&& a):pointer(a.pointer) {
a.pointer = nullptr;
std::cout << "移动" << pointer << std::endl;
}
~A(){
std::cout << "析构" << pointer << std::endl;
delete pointer;
}
};
// 防止编译器优化
A return_rvalue(bool test) {
A a,b;
if(test) return a;
else return b;
if(test) return a; // 等价于 static_cast<A&&>(a);
else return b; // 等价于 static_cast<A&&>(b);
}
int main() {
A obj = return_rvalue(false);

23
code/3/3.4.cpp
View File

@@ -10,22 +10,31 @@
class A {
public:
int *pointer;
A():pointer(new int(1)) { std::cout << "构造" << pointer << std::endl; }
A(A& a):pointer(new int(*a.pointer)) { std::cout << "拷贝" << pointer << std::endl; } // 无意义的对象拷贝
A(A&& a):pointer(a.pointer) { a.pointer = nullptr;std::cout << "移动" << pointer << std::endl; }
~A(){ std::cout << "析构" << pointer << std::endl; delete pointer; }
A():pointer(new int(1)) {
std::cout << "构造" << pointer << std::endl;
}
A(A& a):pointer(new int(*a.pointer)) {
std::cout << "拷贝" << pointer << std::endl;
} // 无意义的对象拷贝
A(A&& a):pointer(a.pointer) {
a.pointer = nullptr;
std::cout << "移动" << pointer << std::endl;
}
~A(){
std::cout << "析构" << pointer << std::endl;
delete pointer;
}
};
// 防止编译器优化
A return_rvalue(bool test) {
A a,b;
if(test) return a;
else return b;
if(test) return a; // 等价于 static_cast<A&&>(a);
else return b; // 等价于 static_cast<A&&>(b);
}
int main() {
A obj = return_rvalue(false);
std::cout << "obj:" << std::endl;
std::cout << obj.pointer << std::endl;
std::cout << *obj.pointer << std::endl;
return 0;
}