c - C 中 ={0} 的长版本是什么？

Question

我被问到这个问题：

= { 0 }是什么更长的代码的“捷径”？

因此，经过多次搜索和翻阅我的 C 书籍后，我知道它对聚合初始化所做的一切，但如果我想编写这段代码的更长版本怎么办。这是程序中的实际代码，以防万一

static char vid[25][100] = { 0 } ;

Answer 1

长版本（你会很难变长）：

static const char vid[25][100] =
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};

也就是说，decl 是静态的，因此一开始就放在零初始化内存中，所以这有点多余，但至少你知道它是什么样子的。

Answer 2

该标准没有定义如何进行归零，因此它是特定于实现的。在实践中，对于局部变量，编译器一般会生成一个memset// RtlZeroMemoryetc。为了这。对于静态/全局变量，不需要代码，因为变量将被放入零初始化内存中。

Answer 3

它一次性将数组的所有元素初始化为 0。否则，您可以想象应变对所有元素单独进行。

Answer 4

长版本是一个初始化数组所有成员的循环：

for (int i = 0; i < ARRAY_SIZE; ++i)
{
    myArray[i] = 0;
}

编译器可能会生成对该函数的调用，该memset函数可能包含也可能不包含此幼稚循环的更优化版本。

但就像迪特里希指出的那样，在您在问题中显示的示例中，您正在声明一个static数组。这让事情变得有点复杂。未初始化的静态数据放置在可执行文件的一个特殊部分中，称为该.bss部分，并且 C 和 C++ 标准都要求将其默认初始化为零。如果显式初始化数据，链接器会将其放入.data可执行文件的部分。显式初始化为 0 有点特殊。智能链接器将省略显式初始化程序并将数据放在.bss节中。哑链接器仍可能将数据放在.data节中。所以最好不要用静态链接显式地对对象进行零初始化。

Answer 5

“大约”你正在做的“非常长”的版本是：

static char vid[25][100];
static firstTime = 1;

if(firstTime) {
  int ii, jj;

  for(ii = 0; i < 25; ii++) {
    for (jj = 0; jj < 100; jj++) {
      vid[ii][jj] = 0;
    }
  }
  firstTime = 0;
}

这考虑到这应该只在第一次完成，因为变量被声明为static. 实际上，正如评论中所指出的，static关键字意味着初始化为零，并映射到称为.bss段的特殊区域。main()在被调用之前，程序加载器或其他一些机制将其设置为零。因此，运行的代码看起来不像上面的代码（内存块归零可以在大多数处理器上非常有效地完成，并且不涉及在多个维度上循环！）。

但：

main初始化是在调用函数之前发生的事情，而我的“近似等效”代码实际上是在执行期间运行的；所以，正如 Jens 所指出的，这并不是一回事。WhozCraig 实际上显示了{0}简写形式的显式启动；这是最好的答案。