如果取消引用new new int会发生什么? [英] What happens if you dereference `new int`?

问题描述

以下安全吗?

*(new int);

我得到的输出为0.

推荐答案

它是未定义的，因为您正在读取具有不确定值的对象.表达式new int()使用零初始化，保证零值，而new int(不带括号)使用默认初始化，为您提供不确定的值.这实际上与说:

It’s undefined because you’re reading an object with an indeterminate value. The expression new int() uses zero-initialisation, guaranteeing a zero value, while new int (without parentheses) uses default-initialisation, giving you an indeterminate value. This is effectively the same as saying:

int x;              // not initialised
cout << x << '\n';  // undefined value

但是，此外，由于您将立即将指针重新引用到刚刚分配的对象，并且不将指针存储在任何地方，因此会造成内存泄漏.

But in addition, since you are immediately dereferencing the pointer to the object you just allocated, and do not store the pointer anywhere, this constitutes a memory leak.

请注意，此类表达式的存在并不一定会使程序格式错误；这是一个非常有效的程序，因为它会在读取对象之前设置对象的值:

Note that the presence of such an expression does not necessarily make a program ill-formed; this is a perfectly valid program, because it sets the value of the object before reading it:

int& x = *(new int);  // x is an alias for a nameless new int of undefined value
x = 42;
cout << x << '\n';
delete &x;

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