Zodiac Wang

二维数组动态初始化以及二维vector的初始化

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可以

int a[3][3];

但不可以

int a[n][m];

所以有动态初始化的需求 使用 new 实现

messet

void * memset ( void * ptr, int value, size_t num );

为特定内存块设置值

erase注意注意事项

vector 或者 string 等 STL 容器，如果调用 erase 方法将其中的某个值删除的话，后序的元素会自动补上前面的空位。

vector::erase

iterator erase (const_iterator position);
iterator erase (const_iterator first, const_iterator last);

参数必须是 iterator 删除 vector 中特定项

#include <iostream>
#include <vector>

using namespace std;

//二维数组初始化
int initialize_dynamic_2d_array()
{
    int n = 3, m = 3;
    int** arr = new int*[n];
    for (int i = 0; i != m; i++)
    {
        arr[i] = new int[m];
        memset(arr[i], 0, m * sizeof(int));//并非必须
    }

    for (int i = 0; i != n; i++)
    {
        for (int j = 0; j != m; j++)
        {
            arr[i][j] = n * i + j;
        }
    }

    for (int i = 0; i != n; i++)
    {
        for (int j = 0; j != m; j++)
        {
            cout << arr[i][j];
        }
    }
    cout << endl << endl;

    return 0;
}


//二维 vector 初始化方法
int initialize_2dvector()
{
    int row = 5, col = 3;
    vector<vector<int>> arr(row);
    for (int i = 0; i != row; i++)
    {
        arr[i].resize(col);
    }

    arr[1][0] = 10;
    //输出2d vector
    for (int i = 0; i != row; i++)
    {
        for (int j = 0; j != col; j++)
        {
            cout << arr[i][j];
        }
    }
    cout << endl << endl;
    return 0;
}

//vector erase 测试
int vector_erase_test()
{
    vector<int> arr_1(10);
    for (int i = 0; i < 10; i++) arr_1[i] = i;
    arr_1.erase(arr_1.begin() + 3);
    for (vector<int>::iterator iter = arr_1.begin(); iter != arr_1.end(); iter++)
    {
        cout << *iter;
    }
    cout << endl << endl;

    int row = 3, col = 3;
    vector<vector<int>> arr_2(row);
    for (int i = 0; i != row; i++)
    {
        arr_2[i].resize(col);
        for (int j = 0; j != arr_2[i].size(); j++)
        {
            arr_2[i][j] = row * i + j;
        }
    }
    cout << "arr_2 size " << arr_2.size() << endl;
    arr_2.erase(arr_2.begin());
    //arr_2 size 实时变小
    arr_2[0].erase(arr_2[0].begin());
    for (int i = 0; i != arr_2.size(); i++)
    {
        for (int j = 0; j != arr_2[i].size(); j++)
        {
            cout << arr_2[i][j];
        }
    }
    cout << endl << "arr_2 size " << arr_2.size();
    cout << endl << endl;

    return 0;
}


int main()
{
    initialize_dynamic_2d_array();
    initialize_2dvector();
    vector_erase_test();
    system("pause");
    return 0;
}

012345678

0001000000000000

012456789

arr_2 size 3 45678 arr_2 size 2

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