Question

#include <stdio.h>

int main(void) {
    for (int i = 0; i < 5; i++) {
        int arr[5] = {0};
        // arr gets zeroed at runtime, and on every loop iteration!
        printf("%d %d %d %d %d
", arr[0], arr[1], arr[2], arr[3], arr[4]);
        // overwrite arr with non-zero crap!
        arr[0] = 3;
        arr[1] = 5;
        arr[2] = 2;
        arr[3] = 4;
        arr[4] = 1;
    }
    return 0;
}

很明显,这项工作:

> gcc -Wall -Wextra -pedantic -std=c99 -o test test.c;./test
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0

但:

What s going on under the hood?
Is this guaranteed to work for arrays of any size?
Have I found the most elegant way of zeroing an array on every iteration of a loop?

Answer 1

此前已经回答:

how does array[100] = {0} set the entire array to 0?

谁在hood?

汇编者将产生相当于肉类的代码(详情见系列图会议。

这是否保证为任何规模的阵列工作?

在你的可用体积限度内,是。

我是否找到了一种最合适的办法,在 lo的每一个角落 zero一阵?

我这样说:

Answer 2

您正在每座播种中建立一个<><>><>>>新><>>>>>>>阵容,因此没有重新开始。

Answer 3

See according to me whenever you are iterating over a loop, then whatever variables you are declaring inside the loop are local to that loop. So at the end of the loop they are getting destroyed, and when the loop is again starting then they are being created again. So, 1. answered above; 2. yes this should work for array of any size; 3. no...

Answer 4

The variable arr is created and initialized on every iteration of the loop because that s what you wrote. In your example, the code does something analogous to memset() to set the array to zero, but possibly more efficiently and inline. You could write a non-zero initializer too.

是的,它针对的是任何大小的阵容。如果阵列越大, lo就将放慢。

这是实现这一效果的非常明智的方法。汇编者将尽快这样做。如果你能够写一份更快捷的职能要求,汇编者作者就已经宣誓就职。

Answer 5

是的,《标准》保证,你的阵列 el在每一处 lo上都是零的。如果你只想将其一度 zero灭,使阵列静态,即:

static int arr[5] = {0};

在此情况下,你可以删除<代码>={0},因为静态数据必须初步化,因为如果没有初始器,所有要素都被分配到0(或UNL为点人,或为浮动点值分配0.0),则重新计算。

请注意,如果您使用less initializers 而不是阵列,则其余部分被分配为零。 So

int arr[5] = {42, 0xdead};

is equivalent to

int arr[5] = {42, 0xdead, 0, 0, 0};

采用单一0办法只是这一规则的一个特殊案例。

Answer 6

我不想忽略该法典的逻辑错误(每个版本都采用)。这是经过尝试和测试的方法,幸运的是,在几乎所有的汇编实施过程中,这些方法都是作为药剂运作的。

MemCpy Example

因此,将采用你的法典;

int a[5]; 
memset(a,0,<number of bytes to be set to> sizeof(int)*5);

请读一下文件,以说明为什么会很快,你将享有......

EDIT Sorry and Thanks for all the down voters / commentors... I corrected the answer...

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