当二维数组和多维数组作为C语言函数参数 [英] When two-dimensional array and multidimensional array as function parameters in C language

问题描述

可能重复：结果
  如何使用数组在C ++？

一维数组作为函数参数：

One dimensional array as a function parameter:

#include <stdio.h>
#include <string.h>

int func(int a[], int n)
{
    int i;
    for(i = 0; i < n; i++)
        printf("%d ", a[i][j]);
}

int main(void)
{   
    int a[2] = {1,2};
    func(a, 2);
}

它编译并运行正常。

it compiles and runs correctly.

但是，当一个二维阵列作为函数参数：

But when a two-dimensional array as a function parameter:

#include <stdio.h>
#include <string.h>

int func(int a[][], int n)
{
    int i, j;
    for(i = 0; i < n; i++)
        for(j = 0 ; j < n; j++)
            printf("%d ", a[i][j]);
        printf("\n");
}

int main(void)
{   
    int a[2][2] = {{1,2}, {3,4}};
    func(a, 2);
}

它不能正确编译。我必须修改code是这样的：

it can not compile correctly. I must modify the code like this:

#include <stdio.h>
#include <string.h>

int func(int a[][2], int n)
{
    int i, j;
    for(i = 0; i < n; i++)
        for(j = 0 ; j < n; j++)
            printf("%d ", a[i][j]);
        printf("\n");
}

int main(void)
{   
    int a[2][2] = {{1,2}, {3,4}};
    func(a, 2);
}

我不知道为什么？任何人都可以解释它如何工作？非常感谢。

I do not know why? Anybody can explain how it works? Many thanks.

推荐答案

阵列（两者之一，多维c）中驻留在连续的内存块。这意味着，当你定义字符一个[3] ，该数组在内存布局是这样的（原谅我的可怕的ASCII艺术技能）：

Arrays (both one and multidimensional) in c reside in continuous memory blocks. This means that when you define char a[3], the array is laid out in memory like this (forgive my terrible ascii art skills):

| a[0] | a[1] | a[2] |

对于一个二维数组一个烧焦[2] [3] ，布局是这样的：

| a[0][0] | a[0][1] | a[0][2] | a[1][0] | a[1][1] | a[1][2] |  
                              ^
                              +--- first row ends here

因此​​，当您索引到一个二维数组 A [I] [J] ，编译器生成code等价于：

Therefore, when you index into a two-dimensional array a[i][j], the compiler generates code equivalent to this:

*(a + i*3 + j)

这可以理解为跳过我行采取行小区j。要做到这一点，编译器必须知道该行的长度（这是第二维）。这意味着，第二个维度是类型定义的一部分！

Which can be read as "skip i rows and take cell j in that row". To accomplish this, the compiler must know the length of the row (which is the second dimension). This means that the second dimension is a part of the type definition!

因此​​，当你想传递一个二维数组到一个函数，你必须指定类型定义所需要的尺寸。

As such when you want pass a 2d array into a function, you must specify the needed dimension for the type definition.

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