c++ - 诠释 x;整数y;诠释*ptr；不是初始化吧？

Question

我正在阅读 J. P. Mueller 和 J. Cogswell 的“C++ All-in-One for Dummies”，偶然发现:

#include <iostream>
using namespace std;
int main()
{
    int ExpensiveComputer;
    int CheapComputer;
    int *ptrToComp;
...

This code starts out by initializing all the goodies involved — two integers and a pointer to an integer.

确认一下，这是一个错误，应该读作“...通过声明”，对吗？让我感到奇怪的是，这些基本错误仍然会出现在书籍中。

Answer 1

从语言的角度来看，这是default initialization .问题是，它们被初始化为不确定的值。

otherwise, nothing is done: the objects with automatic storage duration (and their subobjects) are initialized to indeterminate values.

Default initialization of non-class variables with automatic and dynamic storage duration produces objects with indeterminate values (static and thread-local objects get zero initialized)

请注意，任何读取这些不确定值的尝试都会导致 UB .

根据标准，[dcl.init]/7

To default-initialize an object of type T means:

• If T is a (possibly cv-qualified) class type ([class]), constructors are considered. The applicable constructors are enumerated([over.match.ctor]), and the best one for the initializer () is chosenthrough overload resolution ([over.match]). The constructor thusselected is called, with an empty argument list, to initialize theobject.

• If T is an array type, each element is default-initialized.

• Otherwise, no initialization is performed.