read-numbers-in-a-text-file-into-an-array.md

Multi-Dimensional Arrays

1D vector

#include <stdio.h>
#include <vector>

using namespace std;
int main() {
    vector<int> inputValues = {1,2,3,4}; 
    // Display the vector 方法一
    for (int count = 0; count < inputValues.size(); count++){
        printf("%d ", inputValues[count]);
    }
    printf("\n---------------------------------\n");
    // Display the vector 方法二
    for (int x : inputValues)
        printf("%d ", x);
    printf("\n");
}

輸出結果:

1 2 3 4
---------------------------------
1 2 3 4

2D vector

可以建立一個二維 vector 並給予初值，直接透過 {} 將維度內的元素進行區隔。

#include <stdio.h>
#include <vector>

using namespace std;
#define HEIGHT 2
#define WIDTH 3
int main() {
  vector<vector<int>> inputValues
    {
        {1, 2, 3},
        {4, 5, 6}
    };
          
   // Display the vector 方法一
    for (int i = 0; i < HEIGHT; i++)
        for (int j = 0; j < WIDTH; j++)
            printf("%d ", inputValues[i][j]);
    printf("\n---------------------------------\n");
    // Display the vector 方法二
    for (vector<int> vect1D : inputValues)
    {
        for (int x : vect1D)
        {
            printf("%d ", x);
        }    
    }
    printf("\n");
}

輸出結果:

1 2 3 4 5 6 
---------------------------------
1 2 3 4 5 6 

又或者可以先手動 resize 接著逐一的透過迴圈塞入數值:

#include <stdio.h>
#include <vector>

using namespace std;
#define HEIGHT 2
#define WIDTH 3
int main() {
  vector<vector<float> > array2D;

  // Set up sizes. (HEIGHT x WIDTH)
  array2D.resize(HEIGHT);
  for (int i = 0; i < HEIGHT; i++)
    array2D[i].resize(WIDTH);
  // Insert values
  int index = 0;
  vector<float> inputValues = {1,2,3,4,5,6}; 
  for (int i = 0; i < HEIGHT; i++)
      for (int j = 0; j < WIDTH; j++)
          array2D[i][j] = inputValues[index++];
          
   printf("%f\n", array2D[1][2]); // print last one

}

讀取 txt 數值並儲存陣列

首先建立一個 data.txt 文件，透過空白或換行區隔每個數字。

1 2 3 4 5 6

接著在 main.cpp 中透過 fstream 讀檔，並依序的讀取每個數值並塞入到 vector 陣列中。

#include <stdio.h>
#include <vector>
#include <fstream>

using namespace std;
int main() {
    vector<float> inputValues; 
    std::ifstream file("./data.txt"); 
    while(!file.eof()) 
    {
        double i; 
        file >> i; 
        inputValues.emplace_back(i); 
    }
    // Display the numbers read
    for (int count = 0; count < inputValues.size(); count++){
        printf("%f\n", inputValues[count]);
    }
}

Reference

• 2D Vector In C++ With User Defined Size
• Multi-Dimensional Arrays
• How can I read numbers in a text file into an array in C++?