可是：

Question

我被问到这个问题：

= { 0 }是更长代码的“捷径”吗？

因此，经过我的C书的多次搜索和搜索之后，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较长版本会怎样。以下是程序中的实际代码，以防万一

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

Answer 1

长版本（你很难再延长版本）：

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};

也就是说，decl是静态的，因此首先放在零初始化的内存中，所以这有点多余，但至少你知道它看起来像什么。

Answer 2

标准没有定义如何进行归零，因此它的具体实现。实际上，对于局部变量，编译器通常生成memset / RtlZeroMemory /等。为了这。对于static / globals，不需要代码，因为变量将被置于零初始化内存中。

Answer 3

它将数组的所有元素一次性初始化为0.Else你可以想象为它们所有人单独做的压力。

Answer 4

long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memset函数的调用，该函数可能包含也可能不包含此天真循环的更优化版本。

但就像迪特里希指出的那样，在你在问题中展示的例子中，你宣布了一个static数组。这让事情变得复杂一些。未初始化的静态数据放在可执行文件的一个特殊部分，称为.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，链接器会将其放在可执行文件的.data部分中。显式初始化为0有点特殊情况。智能链接器将省略显式初始值设定项并将数据放在.bss部分中。愚蠢的链接器仍然可以将数据放在.data部分中。因此，使用静态链接显式零对象初始化可能更好 not 。

Answer 5

“近似”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。在main()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，运行的代码看起来并不像上面那样（在大多数处理器上可以非常有效地完成内存归零，并且不涉及多个维度的循环！）。

可是：

初始化是在调用main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所指出的那样，事实并非如此。 WhozCraig实际上显示了{0}是简写的显式首次启发;这是最好的答案。

C中= {0}的长版本是什么？

5 个答案:

可是：