将数组的所有元素初始化为C++中的一个默认值? [英] Initialization of all elements of an array to one default value in C++?

问题描述

C++ Notes: Array Initialization 有一个很好的列表数组的初始化.我有一个

C++ Notes: Array Initialization has a nice list over initialization of arrays. I have a

int array[100] = {-1};

期望它充满 -1 但不是，只有第一个值是，其余的都是 0 与随机值混合.

expecting it to be full with -1's but its not, only first value is and the rest are 0's mixed with random values.

代码

int array[100] = {0};

工作正常并将每个元素设置为 0.

works just fine and sets each element to 0.

我在这里遗漏了什么.如果值不为零，就不能初始化它吗?

What am I missing here.. Can't one initialize it if the value isn't zero ?

还有 2:默认初始化(如上)是否比通常循环遍历整个数组并赋值更快，还是做同样的事情?

And 2: Is the default initialization (as above) faster than the usual loop through the whole array and assign a value or does it do the same thing?

推荐答案

使用你使用的语法，

int array[100] = {-1};

表示将第一个元素设置为 -1，其余元素设置为 0"，因为所有省略的元素都设置为 0.

says "set the first element to -1 and the rest to 0" since all omitted elements are set to 0.

在 C++ 中，要将它们全部设置为 -1，您可以使用类似 std::fill_n(来自<algorithm>):

In C++, to set them all to -1, you can use something like std::fill_n (from <algorithm>):

std::fill_n(array, 100, -1);

在便携式 C 中，您必须滚动自己的循环.有编译器扩展，或者如果可以接受的话，您可以依赖实现定义的行为作为捷径.

In portable C, you have to roll your own loop. There are compiler-extensions or you can depend on implementation-defined behavior as a shortcut if that's acceptable.

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