csv 文件中 C++ 中多维数组的总和

Question

Would anyone be able to help me, I am trying to make a C++ program which reads values from csv file and prints them(there are going to be three 4 rows, 3 columns). I want to know how can I add the rows (like the sum of the first row =? the sum of second-row =?...)

The matrix looks like this:

And my program looks like:

#include <iostream>
#include <fstream>

using namespace std;

int main() {
    
    ifstream sumCol;
    sumCol.open("Col.csv");
    
    string line;
    int sum;
    
    cout << "The entered matrix: " << endl;
    while(sumCol.good()){
        string line;
        getline(sumCol, line, ',');
        cout << line << "  ";
    }

    while(sumCol.good()){
        getline(sumCol, line, ',');
        int i = stoi(line);
        cout << endl; 
        cout << i;
    }
    
    
  while(getline(sumCol, line, ',')){
        int i = stoi(line);
        sum = sum + i;
        
        getline(sumCol, line, ',');
        i = stoi(line);
        sum = sum + i;
        
        getline(sumCol, line);
        i = stoi(line);
        sum = sum + i;
    }
    
    cout << sum << endl;
    
    return 0;
}

Answer 1

Next try. Very simple answer with just basic constructs.

12 statements. But 2 for loops, nested and hardcoded magic numbers for rows and columns.

Please see the below well commented source code:

#include <iostream>
#include <fstream>

int main() {

    // Open file 
    std::ifstream csv("col.csv");

    // and check, if it could be opened
    if (csv) {

        // Now the file is open. We have 3 rows and 4 columns
        // We will use 2 nested for loops, one for the rows and one for the columns

        // So, first the rows
        for (int row = 0; row < 3; ++row) {

            // Every row has a sum
            int sumForOneRow = 0;

            // And every row has 4 columns. Go through all coulmns of the current row.
            for (int col = 0; col < 4; ++col) {

                // Read an integer value from the current line
                int integerValue;
                csv >> integerValue;

                // Show it on the screen
                std::cout << integerValue << ' ';

                // Update the sum of the row
                sumForOneRow = sumForOneRow + integerValue;
            }
            // Now, the inner for loop for the 4 columns is done. Show sum to user
            std::cout << " --> " << sumForOneRow << '\n';

            // Line activities are done now for this line. Go on with next line
        }

    }
    else std::cerr << "\n*** Error: Could not open 'col.csv'\n";
    return 0;
}

Answer 2

Third try.

Obviously the matrix, shown in the question, does not reflect the real data. The real data might look like that:

9, 1, 2, 4
9, 2, 8, 0 
3, 3, 3, 3

Without using std::getline we can do like the below:

#include <iostream>
#include <fstream>

int main() {

    // Open file 
    std::ifstream csv("r:\\col.csv");

    // and check, if it could be opened
    if (csv) {

        // Now the file is open. We have 3 rows and 4 columns
        // We will use 2 nested for loops, one for the rows and one for the columns

        // So, first the rows
        for (int row = 0; row < 3; ++row) {

            // Every row has a sum
            int sumForOneRow = 0;

            // And every row has 4 columns. Go through all coulmns of the current row.
            for (int col = 0; col < 4; ++col) {

                // Read an integer value from the current line
                int integerValue;
                char c; // for the comma

                // The last value, the value in column 3 (We start counting with 0) is not followed by a comma
                // Therefore we add special treatment for the last column
                if (col == 3)
                    csv >> integerValue; // Read just the value
                else
                    csv >> integerValue >> c; // Read value and comma

                // Show it on the screen
                std::cout << integerValue << ' ';

                // Update the sum of the row
                sumForOneRow = sumForOneRow + integerValue;
            }
            // Now, the inner for loop for the 4 columns is done. Show sum to user
            std::cout << " --> " << sumForOneRow << '\n';

            // Line activities are done now for this line. Go on with next line
        }

    }
    else std::cerr << "\n*** Error: Could not open 'col.csv'\n";
    return 0;
}

Answer 3

4th try. Based on the evolution of this thread and the request of the OP to use std::getline

#include <iostream>
#include <fstream>
#include <string>

int main() {

    // Open file 
    std::ifstream csv("r:\\col.csv");

    // and check, if it could be opened
    if (csv) {

        // Now the file is open. We have 3 rows and 4 columns
        // We will use 2 nested for loops, one for the rows and one for the columns

        // So, first the rows
        for (int row = 0; row < 3; ++row) {

            // Every row has a sum
            int sumForOneRow = 0;

            // And every row has 4 columns. Go through all coulmns of the current row.
            for (int col = 0; col < 4; ++col) {

                // Read a substring up to the next comma or end of line
                std::string line;

                // Special handling for last column. This is not followed by a comma
                if (col == 3)
                    std::getline(csv, line);
                else
                    std::getline(csv, line, ',');

                // Convert string to line
                int integerValue = std::stoi(line);

                // Show it on the screen
                std::cout << integerValue << ' ';

                // Update the sum of the row
                sumForOneRow = sumForOneRow + integerValue;
            }
            // Now, the inner for loop for the 4 columns is done. Show sum to user
            std::cout << " --> " << sumForOneRow << '\n';

            // Line activities are done now for this line. Go on with next line
        }

    }
    else std::cerr << "\n*** Error: Could not open 'col.csv'\n";
    return 0;
}

IMHO this is more complicated than 3rd try

Answer 4

Yes, I can help you with a piece of code, but I am not sure, if you will understand the more modern C++ language elements.

So, what do we need to do?

• Read line by line of the source csv string
• Get all integer values for this line
• The interger values are arranged in columns and separated by white space
• Show the values and the screen
• Sum up the values in onbe line and show the sum

And in the resulting code, we will do exactly that.

So, first, we open the file, and check, it it could be opened. Then, in a simple for loop, we read all lines that are present in the source code. Line by line.

In the body of the for loop, we take the current line that we just read, and put it into an std::istringstream . We do that to make extraction of the integer value simpler. And for the extraction, we use the std::istream_iterator . This will iterate over all integers in the line and return them.

We will store the values temporary in a std::vector . We use the range constructor of the std::vector . The begin iterator is the std::istream_iterator for the data type int and and for our std::istringstream . The end iterator is the default constructed std::istream_iterator , so, simply {}. This will copy all values into the std::vector

That is a powerful and compact on-liner.

We copy the values in the std::vector , so, the integer values of one line to the console.

Then, we add up all values in the std::vector (all integers from one line) and show the result on the screen.

And the beauty of it: It doesn't matter, how many rows and columns are present. It will work always. The only thing we need is space separated integer values in lines.

And all this can be done with just 7 statements. . .

Please see:

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
#include <numeric>

int main() {
    // Open file and check, if it could be opened
    if (std::ifstream csv{ "col.csv" }; csv) {

        // Read all lines from the source file
        for (std::string line{}; std::getline(csv, line); ) {

            // Put the current line in a stringstream for better extraction
            std::istringstream iss{ line };

            // Exctract all integer values from this line and put them int a vector
            std::vector values(std::istream_iterator<int>(iss), {});

            // Show values on display
            std::copy(values.begin(), values.end(), std::ostream_iterator<int>(std::cout, " "));

            // Claculate the sum for one line on show on display.
            std::cout << " --> " << std::accumulate(values.begin(), values.end(), 0) << '\n';
        }
    }
    else std::cerr << "\n*** Error: Could not open 'col.csv'\n";
    return 0;
}

Language is C++ 17