[英]Assignment operator - Self-assignment
Does the compiler generated assignment operator guard against self assignment? 编译器是否为自我赋值生成了赋值操作符?
class T {
int x;
public:
T(int X = 0): x(X) {}
};
int main()
{
T a(1);
a = a;
}
Do I always need to protect against self-assignment even when the class members aren't of pointer type? 即使班级成员不是指针类型,我是否总是需要防止自我分配?
Does the compiler generated assignment operator guard against self assignment?
编译器是否为自我赋值生成了赋值操作符?
No, it does not. 不,不是的。 It merely performs a member-wise copy, where each member is copied by its own assignment operator (which may also be programmer-declared or compiler-generated).
它仅执行成员方式的副本,其中每个成员都由其自己的赋值运算符(也可能是程序员声明的或编译器生成的)复制。
Do I always need to protect against self-assignment even when the class members aren't of pointer type?
即使班级成员不是指针类型,我是否总是需要防止自我分配?
No, you do not if all of your class's attributes (and therefore theirs) are POD-types . 不,如果您的所有类属性(以及它们的属性)都是POD类型 ,则不会。
When writing your own assignment operators you may wish to check for self-assignment if you want to future-proof your class, even if they don't contain any pointers, et cetera . 在编写自己的赋值运算符时,如果您希望在未来证明您的类,即使它们不包含任何指针,也可以检查自我赋值等等 。 Also consider the copy-and-swap idiom .
还要考虑复制和交换习语 。
This is an easy one to check empirically: 这是一个很容易根据经验检查:
#include <iostream>
struct A {
void operator=(const A& rhs) {
if(this==&rhs) std::cout << "Self-assigned\n";
}
};
struct B {
A a;
};
int main()
{
B b;
b = b;
}
class T {
int x;
public:
T(int X = 0): x(X) {}
// prevent copying
private:
T& operator=(const T&);
};
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