二維陣列
初始化
初始化方法1
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int arr[2][3] = { {1,2,3}, {4,5,6} };
cout << "arr[0][0] = " << arr[0][0] << endl;
cout << "arr[0][1] = " << arr[0][1] << endl;
cout << "arr[0][2] = " << arr[0][2] << endl;
cout << "arr[1][0] = " << arr[1][0] << endl;
cout << "arr[1][1] = " << arr[1][1] << endl;
cout << "arr[1][2] = " << arr[1][2] << endl;
arr[0][0] = 1
arr[0][1] = 2
arr[0][2] = 3
arr[1][0] = 4
arr[1][1] = 5
arr[1][2] = 6
初始化方法2
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int arr[2][3] = {1,2,3,4,5,6};
cout << "arr[0][0] = " << arr[0][0] << endl;
cout << "arr[0][1] = " << arr[0][1] << endl;
cout << "arr[0][2] = " << arr[0][2] << endl;
cout << "arr[1][0] = " << arr[1][0] << endl;
cout << "arr[1][1] = " << arr[1][1] << endl;
cout << "arr[1][2] = " << arr[1][2] << endl;
初始化方法3
第1個[]中不用寫長度，第2個[]中要寫長度。
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int arr[][3] = {1,2,3,4,5,6};
cout << "arr[0][0] = " << arr[0][0] << endl;
cout << "arr[0][1] = " << arr[0][1] << endl;
cout << "arr[0][2] = " << arr[0][2] << endl;
cout << "arr[1][0] = " << arr[1][0] << endl;
cout << "arr[1][1] = " << arr[1][1] << endl;
cout << "arr[1][2] = " << arr[1][2] << endl;
C11之後不用有等號
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int arr[][3]{1,2,3,4,5,6};
以上印出結果都是一樣。
sizeof
sizeof在二維陣列的使用方式是取出陣列占記憶體全部的byte。
以下的例子二維陣列有6個元素，每個元素是整數4byte，所以陣列占的記憶體大小為6*4 = 24
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int arr[][3] {1,2,3,4,5,6};
cout << "arr size = " << sizeof(arr) << endl;
arr size = 24
二維陣列轉成一維陣列
- 2維陣列記憶體位址是連續
- 把陣列名指派給指標，是把陣列[0][0]的記憶體位址指派給指標
- 使用指標把連續的記憶體位址中的值印出來。
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#include <iostream>
using namespace std;
int main() {
//宣告陣列長度，初始化陣列全部元素為整數0
int arr[2][3] = {0};
//指派值到二維陣列
arr[0][0] = 1;
arr[0][1] = 2;
arr[0][2] = 3;
arr[1][0] = 4;
arr[1][1] = 5;
arr[1][2] = 6;
//印出值
cout << "arr[0][0] = " << arr[0][0] << endl;
cout << "arr[0][1] = " << arr[0][1] << endl;
cout << "arr[0][2] = " << arr[0][2] << endl;
cout << "arr[1][0] = " << arr[1][0] << endl;
cout << "arr[1][1] = " << arr[1][1] << endl;
cout << "arr[1][2] = " << arr[1][2] << endl;
//記憶體位址是連續
cout << "arr[0][0]位址 = " << (long long)&arr[0][0] << endl;
cout << "arr[0][1]位址 = " << (long long)&arr[0][1] << endl;
cout << "arr[0][2]位址 = " << (long long)&arr[0][2] << endl;
cout << "arr[1][0]位址 = " << (long long)&arr[1][0] << endl;
cout << "arr[1][1]位址 = " << (long long)&arr[1][1] << endl;
cout << "arr[1][2]位址 = " << (long long)&arr[1][2] << endl;
//因為記憶體位址都是連續的，把二維陣列[0][0]記憶體位址指派給指標p
int* p = (int*)arr;
//取得arr變數記憶體大小
int size = sizeof(arr) / sizeof(int);
for (int i = 0; i < size; i++) {
//使用指標運算印出每個元素的值
cout << "*(p + " << i << ") = " << *(p+i) << ",";
//使用索引方式印出值
cout << " [" << i << "] = " << p[i] << endl;
}
return 0;
}
arr[0][0] = 1
arr[0][1] = 2
arr[0][2] = 3
arr[1][0] = 4
arr[1][1] = 5
arr[1][2] = 6
arr[0][0]位址 = 140702053823568
arr[0][1]位址 = 140702053823572
arr[0][2]位址 = 140702053823576
arr[1][0]位址 = 140702053823580
arr[1][1]位址 = 140702053823584
arr[1][2]位址 = 140702053823588
*(p + 0) = 1, [0] = 1
*(p + 1) = 2, [1] = 2
*(p + 2) = 3, [2] = 3
*(p + 3) = 4, [3] = 4
*(p + 4) = 5, [4] = 5
*(p + 5) = 6, [5] = 6
從以上結果可以發現，記憶體位址的差距為4byte，而且是連續的。
可以使用指標把二維陣列轉成一維指標陣列，印出值。
指標指向二維陣列
二維陣列可以解釋為，一維陣列，裡面每一個元素又指向一維陣列。
宣告方式
資料類型 (*指標變數)[二維陣列每個元素所指向的一維陣列大小] = 二維陣列變數名;
使用二維陣列指標一定要把*指標變數用括號()包起來，因為有運算子優先順序的問題。
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int main() {
//[3]代表二維陣列每個元素是大小為3的一維陣列。
int arr[2][3] = { {1,2,3},{4,5,6} };
//[3]代表二維陣列每個元素是大小為3的一維陣列。
int (*p)[3] = arr;
return 0;
}
上一個程式碼例子 ，指標是指向二維陣列int[2][3]，無法轉成指向一維陣列的指標int*，所以要強制轉型成指向一維陣列的指標(int*)二維陣列變數名
以下程式碼原本指向一維陣列的指標，指向二維陣列會編譯錯誤。
//二維陣列
int arr[2][3] = {0};
//原本指向一維陣列的指標，直接指向二維陣列會編譯錯誤
int* p = arr;
Cannot initialize a variable of type ‘int *’ with an lvalue of type ‘int[2][3]’
二維陣列先轉成一維陣列，使用(int*)，再讓指標指向轉型成一維的陣列。
int arr[2][3] = {0};
int* p = (int*)arr;
二維陣列傳函式
方法有二種
- 指標方式 void func(int (*p)[3], int len);
- 陣列方式 void func(int p[][3], int len);
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#include <iostream>
using namespace std;
void func(int (*p)[3], int len) {
for (int i = 0; i < len; i++) {
for (int j = 0; j < 3; j++) {
cout << "p[" << i << "][" << i << "] = " << p[i][j] << "\t";
}
cout << endl;
}
}
int main() {
//[3]代表每個元素是大小為3的一維陣列。
int arr[2][3] = { {1,2,3},{4,5,6} };
func(arr, 2);
return 0;
}
p[0][0] = 1 p[0][0] = 2 p[0][0] = 3
p[1][1] = 4 p[1][1] = 5 p[1][1] = 6
指標指向三維陣列
宣告方式
資料類型 (*指標變數)[陣列個數][元素個數] = 三維陣列變數名;
三維陣列傳函式的方法有二種
- 指標方式
void func(int (*p)[2][3], int len);
- 陣列方式
void func(int p[][2][3], int len);
印出陣列元素
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#include <iostream>
using namespace std;
void func(int (*p)[2][3], int len) {
for (int i = 0; i < len; i++) {
for (int j = 0; j < 2; j++) {
for (int k = 0; k < 3; k++) {
cout << "p[" << i << "][" << j << "][" << k << "] = " << p[i][j][k] << "\t";
}
cout << endl;
}
cout << endl;
}
}
int main() {
int arr[2][2][3] =
{
{ {1,2,3}, {4,5,6} },
{ {7,8,9}, {10,11,12} }
};
func(arr, 2);
return 0;
}
p[0][0][0] = 1 p[0][0][1] = 2 p[0][0][2] = 3
p[0][1][0] = 4 p[0][1][1] = 5 p[0][1][2] = 6
p[1][0][0] = 7 p[1][0][1] = 8 p[1][0][2] = 9
p[1][1][0] = 10 p[1][1][1] = 11 p[1][1][2] = 12
修改陣列元素
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#include <iostream>
using namespace std;
const int firstMax = 2;
const int secondMax = 2;
const int thirdMax = 3;
void modifyArr(int p[][secondMax][thirdMax], int len) {
for (int i = 0; i < len; i++) {
for (int j = 0; j < secondMax; j++) {
for (int k = 0; k < thirdMax; k++) {
//修改指標記憶體位址的值
p[i][j][k] += 10;
}
}// end of j
}// end of i
}
void printArr(int (*p)[secondMax][thirdMax], int len) {
for (int i = 0; i < len; i++) {
for (int j = 0; j < secondMax; j++) {
for (int k = 0; k < thirdMax; k++) {
cout << "p[" << i << "][" << j << "][" << k << "] = " << p[i][j][k] << "\t";
}
cout << endl;
}// end of j
cout << endl;
}//end of i
}
int main() {
int arr[firstMax][secondMax][thirdMax] =
{
{ {1,2,3}, {4,5,6} },
{ {7,8,9}, {10,11,12} }
};
modifyArr(arr, firstMax);
printArr(arr, firstMax);
return 0;
}
p[0][0][0] = 11 p[0][0][1] = 12 p[0][0][2] = 13
p[0][1][0] = 14 p[0][1][1] = 15 p[0][1][2] = 16
p[1][0][0] = 17 p[1][0][1] = 18 p[1][0][2] = 19
p[1][1][0] = 20 p[1][1][1] = 21 p[1][1][2] = 22