用C未初始化结构 [英] Uninitialized Structures in C

问题描述

在C全局或静态结构的成员的保证被自动初始化为零，在同样的方式，<一href=\"http://stackoverflow.com/questions/1597405/what-happens-to-a-declared-uninitialized-variable-in-c-does-it-have-a-value\">uninitialized全局或静态变量的？

Are the members of a global or static structure in C guaranteed to be automatically initialized to zero, in the same way that uninitialized global or static variables are?

推荐答案

从C99标准6.7.8 / 10初始化：

From the C99 standard 6.7.8/10 "Initialization":

如果具有自动的对象
  存储期未初始化
  明确地说，它的值是
  不定。如果具有一个对象
  静态存储持续时间不
  显式初始化，则：

If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate. If an object that has static storage duration is not initialized explicitly, then:

- 如果它有指针的类型，它是
  初始化为空指针;结果
     - 如果
  它具有算术类型，它是
  初始化为（正或无符号的）
  零;结果
     - 如果它是一个聚合，每
  成员被初始化（递归）
  根据这些规则;结果
    - 如果是
  工会，第一个命名成员
  （递归）根据初始化
  这些规则

— if it has pointer type, it is initialized to a null pointer;
— if it has arithmetic type, it is initialized to (positive or unsigned) zero;
— if it is an aggregate, every member is initialized (recursively) according to these rules;
— if it is a union, the first named member is initialized (recursively) according to these rules

由于全局和静态结构具有静态存储持续时间，答案是肯定的 - 它们是零初始化（在该结构的指针将被设置为NULL指针值，这通常是零比特，但严格来说并不需要定）。

Since globals and static structures have static storage duration, the answer is yes - they are zero initialized (pointers in the structure will be set to the NULL pointer value, which is usually zero bits, but strictly speaking doesn't need to be).

在C ++ 2003标准也有类似的规定（3.6.2非本地对象的初始化）：

The C++ 2003 standard has a similar requirement (3.6.2 "Initialization of non-local objects"):

与静态存储时间（3.7.1）的对象应是零初始化（8.5）之前的任何其他初始化发生。

Objects with static storage duration (3.7.1) shall be zero-initialized (8.5) before any other initialization takes place.

有时是零初始化发生之后，构造函数的调用（如果该对象有一个构造函数）下支配这些电话的时间和顺序的较为复杂的规则。

Sometime after that zero-initialization takes place, constructors are called (if the object has a constructor) under the somewhat more complicated rules that govern the timing and ordering of those calls.

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