2D array size problem loading from csv file

问题

int main()
{

    auto base_dir = fs::current_path();
    auto dataset_1 = data_names_1;
    auto dataset_name = base_dir / "NAimg_20101026_145727.csv";

    //double data[10][3];
    std::ifstream file(dataset_name);

    matrix<DataType> data_length;
    file >> data_length;
    
    auto pre_num_row = data_length.nc();
    static const int num_row = 73;//data_length.nr();
    static const int num_column = 74496; //data_length.nc();

    std::cout << num_row << "\n";
    std::cout << num_column << "\n";

    double data[73][74496];

    for (int row = 0; row < 73; ++row)
    {
        std::string line;
        std::getline(file, line);
        if (!file.good())
            break;

        std::stringstream iss(line);

        for (int col = 0; col < 74496; ++col)
        {
            std::string val;
            std::getline(iss, val, ',');
            if (!iss.good())
                break;

            std::stringstream convertor(val);
            convertor >> data[row][col];
        }
    }

    std::cout << data[1][1] << "\n";
  
}

Hello, My name is Q. I want to read a csv file (here the name of the file is NAimg_20101026_145727.csv) and load the data to data array. The size of row and column of the file is 73 and 74496. Therefore, I need double data[73][74496] array. It makes error. When I make a small array, for example, double data[10][20], there is no error. Do you know what is the problem?

I have one more issue. I want to read the size of row and column from csv file and automatically decide the size of double data[row][column]. Therefore, I tried to use data_length.nc(); to decide the row and column of the double data size. Do you know how to decide the size of double data[row][column] from csv file? Thanks

回答1:

It seems that you'd like to create your 2D array based on data_length.nr() and data_length.nc() that may only be known at runtime so you want dynamic allocation. One simple way to do this is to #include <vector> and create it like this:

#include <vector>

// ...

    // create a 2D vector from nr() and nc()
    std::vector<std::vector<double>> data(data_length.nr(), 
                                          std::vector<double>(data_length.nc()));
    
    // fill the 2D vector with data from the file using range-based for loops:
    // Assuming csv lines formatted like: 1,2,3,4,5<newline>6,7,8,9,10<newline> ...
    for(auto& row : data) {
        for(auto& col : row) {
            file >> col;
            file.ignore(); // ignore one char (commas and newlines)
        }
    }

    if(file) {
        // successfully read the data from the file
        std::cout << data[1][1] << '\n';

    } else {
        std::cout << "failed extracting data from file\n";
    }

回答2:

The data array is placed on the stack, which is limited in size. My version allocates the array on the heap. But I guess you could add c++ operators.

#include <iostream>

#include <stdlib.h>

typedef struct DoubleArray2D{
    int width = 0;
    int height = 0;
    double *data = NULL;
    void allocate(int rows, int columns){
        width = rows;
        height = columns;
        data = (double *)malloc(sizeof(double)*width*height);
    }
    void deallocate(){
        width = 0;
        height = 0;
        free(data);
    }

    double get(int row,int column){
        return data[column*height+row];
    }

    void set(int row, int column,double value){
        data[column*height+row] = value;
    }
}DoubleArray2D;
int main(){
    DoubleArray2D data;
    data.allocate(73,74496);

    data.set(1,1,20.0f);

    std::cout << data.get(1,1) << std::endl;
    data.deallocate();
}

来源：https://stackoverflow.com/questions/65499929/2d-array-size-problem-loading-from-csv-file