初始化阴影变量

问题描述

标准中是否有定义从其隐藏的变量中初始化变量的任何内容?

Is there anything in the standard that defines initialing a variable from the variable it shadows?

例如:

int i = 7;
{
    int i = i;
}

Visual Studio 2013允许这样做而不会发出警告，并且可以按预期工作.内部的i变量是7.Clang和GCC但是给我一个警告，关于从其自身进行初始化的初始化变量将不会被初始化.

Visual Studio 2013 allows this without a warning and works as expected. The inner i variable is 7. Clang and GCC however give me a warning about a initializing variable initializing from itself will be uninitialized.

推荐答案

标准说:

1 名称的声明点紧随其完整的声明符之后 (第8条)及其初始化器(如果有)之前，除非另有说明. [示例:

1 The point of declaration for a name is immediately after its complete declarator (Clause 8) and before its initializer (if any), except as noted below. [ Example:

int x = 12;
{ int x = x; }

这里第二个x被初始化 具有自己的(不确定的)价值. —完示例]

Here the second x is initialized with its own (indeterminate) value. —end example ]

这正是您的情况.该程序通过访问未初始化的对象表现出未定义的行为.

This is precisely your case. The program exhibits undefined behavior by way of accessing an uninitialized object.

我的VS2013副本为此代码报告了error C4700: uninitialized local variable 'i' used.不确定为什么您的副本会表现出不同的行为.

My copy of VS2013 reports error C4700: uninitialized local variable 'i' used for this code. Not sure why your copy behaves differently.

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