Two-dimensional array piecemeal knowledge sorting

Table of Contents

Foreword

Structures of one- and two-dimensional arrays

2. Arrays as function parameters

1. One-dimensional array parameter transfer

2. Two-dimensional array parameter transfer

Three, use pointer to control two-dimensional array

Summary

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Foreword

Hello, everyone.The structure of two-dimensional arrays in C language is more complicated, especially after combining with pointers.Since I have been learning C++ recently, I feel unfamiliar with some knowledge of two-dimensional arrays, so I wrote a blog to summarize this knowledge.

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Structure of one- and two-dimensional arrays

We can understand a two-dimensional array as a one-dimensional array first, and then the element type of the one-dimensional array is also a one-dimensional array, that is, a nested array in an array.

Understand each row as an independent array, arr[i] selects the array in row i, and arr[i][j] selects the jth element in row i.

How is the two-dimensional array distributed in memory?

int main(){int arr[3][3] = { {1,2,3},{4,5,6},{7,8,9} };for (int i = 0; i < 3; i++){for (int j = 0; j< 3; j++){printf("%p\n", &arr[i][j]);}}}

After printing, it is found that the two-dimensional array is continuously distributed in the memory, but for the convenience of understanding, we imagine it as two-dimensional.

2. Arrays as function parameters

1. One-dimensional array parameter transfer

Let's take a look at one-dimensional array parameters first.

int size(int arr[]) //int size(int* arr){return sizeof(arr);}int main(){int arr[3];int size1=sizeof(arr);int size2 = size(arr);printf("%d %d", size1,size2);}

It can be seen from the results that when an array is used as a function parameter, the function will not stupidly copy the entire array, but will take the address of the first element of the array.Therefore, the parameters of the one-dimensional array parameter transfer function can be written as either an array or a pointer. Anyway, the address of the first element is passed in the past.

2. Two-dimensional array parameter transfer

In the one-dimensional array arr, arr is equivalent to the address of the first element, which is equivalent to &arr[0].And &arr is equivalent to the address of the entire array, dereferencing the entire array is equal to the address of the first element (to be honest, I don't know why, but the syntax is so prescribed), if you want to accept the address of the entire element, you must use the array pointer.

In the two-dimensional array arr, analogous to a one-dimensional array, arr is the address of the first element, and the first element of the two-dimensional array is the first row of the array, so arr is the address of the entire first row of the array.Therefore, the two-dimensional array parameter is received by a two-dimensional array or by an array pointer.

void test1(int arr[][3])//It is the same as when the two-dimensional array is defined, the number of row elements can be omitted, and the column cannot be{}void test2(int(*p)[3]){}int main(){int arr[3][3];test1(arr);test2(arr);}

Third, use a pointer to control a two-dimensional array

For the two-dimensional array arr, arr is the address of the first row of the array, arr+i is the address of the i-th row array, and *(arr+i) is the address of the first element of the i-th row array (mentioned above, the address dereference of an array is equal to the address of the first element).So *(*(arr+i)+j) gets the element arr[i][j].

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Summary

That's all for today.This article mainly explains some confusing pieces of knowledge about two-dimensional arrays, hoping to help you.Thank you for reading, I have a long time in Japan, and I look forward to seeing you next time.