指针运算和C 2-D数组？ [英] Pointer arithmetic and 2-D array in c?

问题描述

我是新的C和被困的如何多维数组传递给函数。我也明白，你必须通过列大小，这样，如果你想从走了[0] [0] 到 A [1] [ 0] 它可以计算一维数组的大小，可以跳过去。

I am new to C and got stuck on "How to pass multidimensional array to a function". I do understand that you have to pass column size so that if you want to go from a[0][0] to a[1][0] it can calculate the size of 1-D array and can jump over it.

我已经写了一个小程序：

I have written a small program:

#include<stdio.h>
void foo(char[][2]);
int main()
{
     char arr[2][2] = {'a','b','c','d'};

     foo(arr);
     return 0;
}

void foo(char temp[][2])
{
      temp++;
      printf("%c",*temp);
}

我预计这一code将打印的信 C ，因为温度最初指向'A'，一旦我们增加它，它会跳过第一个一维数组，然后转到第二个1-D数组的第一个元素是'C 。但它不是这样的，我猜。

I expected that this code will print the letter c, since temp initially points to 'a' and once we increment it, it will skip over first 1-d array and go to first element of second 1-d array which is 'c'. But it does not work that way I guess.

请解释编译器如何计算这些地址。

Please explain the how compiler computes these addresses.

推荐答案

有关函数的参数字符临时[] [2] ，温度衰变为指针。但仅用于第一（外）尺寸。因此，它实际上是一个的指针数组 [2] 字符的的

For function argument char temp[][2], temp decays to a pointer. But only for the first (outer) dimension. So it is effectively a pointer to array [2] of char.

递增指针将其推进到一个新的外部指标，因为你已经承担。

Incrementing the pointer will advance it to the next outer index, as you already assumed.

所以，你要么必须使用（*临时）[0] 或 **温度来获得第一个元素。 **温度的作品，因为 *温度本身就是一个数组，所以它衰变为指针的第一个元素内部数组。第二个（左） * 然后取消引用该指针： C

So, you either have to use (*temp)[0] or **temp to get the first element. **temp works, because *temp is an array itself, so it decays to a pointer to the first element of the inner array. The second (left) * then dereferences this pointer: c.

需要注意的是，它allthough使用相同的语法像的char **温度，它们是根本不同的。指针是不是一个数组，在这里，递增温度将仅由一个指针的大小，这是不是你想要的进步。

Note that, allthough it uses the same syntax like char **temp, they are fundamentally different. A pointer is not an array and here, incrementing temp will only advance by the size of a pointer, which is not what you want.

注意，初始化将更好地根据2 simensional性质是：

Note that the initializer would better be according to the 2-simensional nature:

{ { 'a', 'b' } , { 'c', 'd' } }

这确保您获得正确的值的内部数组，是很好的做法。在非嵌套形式省略值将导致错误的序列用于内阵列。当已启用推荐的警告（ -Wall ）的至少，GCC发出警告缺少括号。

This ensures you get the correct values for the inner arrays and is good practice. Omitting a value in the non-nested form will result in wrong sequence for the inner array. When having enabled the recommended warnings (-Wall) at least, gcc warns about missing braces.

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