C++ vector::resize()用法及代碼示例

向量被稱為動態數組，當插入或刪除元素時可以自動更改其大小。該存儲由容器維護。

vector::resize()

該函數通過插入或刪除容器中的元素來實際更改容器的內容。事情是這樣發生的，

如果給定的 n 值小於當前的大小，則多餘的元素將被拆除。
如果 n 大於容器的當前大小，則即將到來的元素將附加到向量的末尾。

用法:

vectorname.resize(int n, int val)

以下示例程序旨在說明該函數的工作原理

1.矢量容器的尺寸減小。

CPP


// resizing of the vector
#include <iostream>
#include <vector>
using namespace std;
int main()
{
    vector<int> vec;
    // 5 elements are inserted
    // in the vector
    vec.push_back(1);
    vec.push_back(2);
    vec.push_back(3);
    vec.push_back(4);
    vec.push_back(5);
    cout << "Contents of vector before resizing:"
         << endl;
     
    // displaying the contents of the
    // vector before resizing
    for (int i = 0; i < vec.size(); i++)
        cout << vec[i] << " ";
    cout << endl;
    // vector is resized
    vec.resize(4);
    cout << "Contents of vector after resizing:"
         << endl;
     
    // displaying the contents of the
    // vector after resizing
    for (int i = 0; i < vec.size(); i++)
        cout << vec[i] << " ";
    return 0;
}

輸出

Contents of vector before resizing:
1 2 3 4 5 
Contents of vector after resizing:
1 2 3 4

2.矢量容器的大小增加。

CPP


// resizing of the vector
#include <iostream>
#include <vector>
using namespace std;
int main()
{
    vector<int> vec;
    // 5 elements are inserted 
    // in the vector
    vec.push_back(1);
    vec.push_back(2);
    vec.push_back(3);
    vec.push_back(4);
    vec.push_back(5);
    cout << "Contents of vector before resizing:"
         << endl;
     
    // displaying the contents of the
    // vector before resizing
    for (int i = 0; i < vec.size(); i++)
        cout << vec[i] << " ";
    cout << endl;
    // vector is resized
    vec.resize(8);
    cout << "Contents of vector after resizing:"
         << endl;
    // displaying the contents of 
    // the vector after resizing
    for (int i = 0; i < vec.size(); i++)
        cout << vec[i] << " ";
    return 0;
}

輸出

Contents of vector before resizing:
1 2 3 4 5 
Contents of vector after resizing:
1 2 3 4 5 0 0 0

3.增加向量容器的大小，並使用指定值初始化新元素。

CPP


// resizing of the vector
#include <iostream>
#include <vector>
using namespace std;
int main()
{
    vector<int> vec;
    // 5 elements are inserted
    // in the vector
    vec.push_back(1);
    vec.push_back(2);
    vec.push_back(3);
    vec.push_back(4);
    vec.push_back(5);
    cout << "Contents of vector before resizing:"
         << endl;
    // displaying the contents of 
    // the vector before resizing
    for (int i = 0; i < vec.size(); i++)
        cout << vec[i] << " ";
    cout << endl;
    // vector is resized
    vec.resize(12, 9);
    cout << "Contents of vector after resizing:"
         << endl;
     
    // displaying the contents 
    // of the vector after resizing
    for (int i = 0; i < vec.size(); i++)
        cout << vec[i] << " ";
    return 0;
}

輸出

Contents of vector before resizing:
1 2 3 4 5 
Contents of vector after resizing:
1 2 3 4 5 9 9 9 9 9 9 9

如何在 2D 矢量(矢量的矢量)的情況下調整大小？

方法/遵循的步驟 - 種類 1：

我們可以先調整外容器向量<vector<int>>的大小
通過這樣做，我們把它變成了 { { }, { }, { } }
然後我們將初始化內部容器。

vector.resize(n, value);

C++


//Resizing a 2D Vector / Matrix
#include <bits/stdc++.h>
using namespace std;
void displayMatrix(vector<vector<int>> v){
    int N = v.size();
    int M = v[0].size();
    for(int i=0; i<N; i++){
        for(int j=0; j<M; j++){
            cout<<v[i][j]<<" ";
        }
        cout<<"\n";
    }
}
int main()
{
     
    vector<vector<int>> v;
     
    cout<<"N: "<<v.size()<<"\n"; //4
     
    v.resize(4, vector<int> (4, -1));
     
    cout<<"N: "<<v.size()<<" M: "<<v[0].size()<<"\n"; //4
    displayMatrix(v);
    return 0;
}
//Code done by Balakrishnan R (rbkraj000)

輸出

N: 0
N: 4 M: 4
-1 -1 -1 -1 
-1 -1 -1 -1 
-1 -1 -1 -1 
-1 -1 -1 -1

另一種方法 - Variety-2：

C++


//Resizing a 2D Vector / Matrix
#include <bits/stdc++.h>
using namespace std;
void displayMatrix(vector<vector<int> > v)
{
    int N = v.size();
    int M = v[0].size();
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
            cout << v[i][j] << " ";
        }
        cout << "\n";
    }
}
int main()
{
    vector<vector<int> > v;
    cout << "N: " << v.size() << "\n"; // 4
    v.resize(4);
    for (int i = 0; i < 4; i++)
        v[i].resize(4, -1);
    cout << "N: " << v.size() << " M: " << v[0].size()
         << "\n"; // 4
    displayMatrix(v);
    return 0;
}
//Code done by Balakrishnan R (rbkraj000)

輸出

N: 0
N: 4 M: 4
-1 -1 -1 -1 
-1 -1 -1 -1 
-1 -1 -1 -1 
-1 -1 -1 -1

本文中的上述 2 種方法由 Balakrishnan R. 貢獻。

相關用法

注：本文由純淨天空篩選整理自akash1295大神的英文原創作品 vector : : resize() in C++ STL。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。