C ++代码中的这个struct X有什么问题? [英] What is wrong with this struct X in C++ code?
问题描述
我把这个问题作为家庭作业。
它按预期方式编译并运行,但是我应该发现它有问题,尽管与const无关。
I got this question as a homework assignment. It compiled and ran as expected and yet I'm supposed to find something wrong with it, though nothing to do with the const.
我知道这是一个结构,所以我的变量都是公共的-这不是问题。我认为这可能与构造函数中使用的新有关。
我很想听听您的想法。
I know this is a struct so my variables are all public - that is not the problem. I thought perhaps it is related to the "new" used in the constructor. I would love to hear your thoughts.
struct X
{
explicit X(int);
~X();
void Foo();
void Bar() const;
int m_a;
int *m_p;
};
X::X(int a_): m_a(a_), m_p(new int(a_)){}
X::~X()
{
delete m_p;
m_p = NULL;
}
void X::Foo()
{
++m_a;
--(*m_p);
}
void X::Bar() const
{
std::cout<<m_a<<std::endl;
std::cout<<*m_p<<std::endl;
std::cout<<m_p<<std::endl;
}
void Fifi(const X& x_)
{
x_.Bar();
}
int main (void)
{
X x1(1);
x1.Foo();
Fifi(x1);
return 0;
}
推荐答案
您的课程违反了三个规则。
完全按照书面规定它并没有什么坏处,但是涉及 X
的看起来无害的构造可能会导致神秘的错误(由于各种形式的不确定行为)。
Your class violates the rule of three.
Exactly as written it doesn't do anything bad, but seemingly harmless constructs involving X
may cause mysterious errors (due to various forms of undefined behaviour).
X a(1), b = a;
在我的机器上,上述行会导致
On my machine the above line causes
*** Error in `./a.out': double free or corruption (fasttop): 0x0000000000dfec20 ***
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