如何使用C ++从CSV文件读取某些列？

Question

I would like to know how to read information from an Excel file (saved as .csv) for then printing it into another file, using C++.

The input file has the data separated into columns. The first line of each column is the label of the column. Such as this:

|Column1|Column2|Column3|Column4|Column5|Column6
|char1.1|char2.1|       |       |       |char6.1
|char1.2|char2.2|int3.2 |char4.2|bool5.2|char6.2
|char1.3|char2.3|int3.3 |char4.3|bool5.3|char6.3
|char1.4|char2.4|       |       |       |char6.4
|char1.5|char2.5|       |       |       |char6.5
|char1.6|char2.6|int3.6 |char4.6|bool5.6|char6.6

So from this table, I would like to extract the columns 3, 4 and 5 (only when there is information, so lines 2,3 and 6) and print the information into another csv file, such as this:

|Column3|Column4|Column5|
|int3.2 |char4.2|bool5.2|
|int3.3 |char4.3|bool5.3|
|int3.6 |char4.6|bool5.6|

Answer 1

strtok is standard function to do that.

#include <stdio.h>
#include <string.h>

int main ()
{
// Read the file ----------
  FILE* fp = fopen("toto.csv", "rb");
  if (fp == NULL) return 0;
  fseek(fp, 0, SEEK_END);
  long size = ftell(fp);
  fseek(fp, 0, SEEK_SET);
  char *pData = new char[size + 1];
  fread(pData, sizeof(char), size, fp);
  fclose(fp);
// Read the file ----------

// Parse the file content ----------
  char* pch;
  pch = strtok (pData, "|");
  while (pch != NULL)
  {
    printf ("%s\n", pch);
    pch = strtok (NULL, "|");
  }
// Parse the file content ----------  
  return 0;
}

You're welcome ! If you want to filter on some columns, then, since strtok doesn't take in argument the column number, you will have to use a conditional statement like if, switch (for a specific treatment depending column etc)

For you example:

  char* pch;
  pch = strtok (pData, "|");
  int iCpt = 1;
  while (pch != NULL)
  {
    if (iCpt == 3 || iCpt == 4 || iCpt == 5)
    {
      printf ("%s\n", pch);
    }
    pch = strtok (NULL, "|");
    iCpt++;
  }

Or using switch, allowing a specific treatment on each column:

  char* pch;
  pch = strtok (pData, "|");
  int iCpt = 1;
  while (pch != NULL)
  {
    switch(iCpt)
    {
      case 3:
      case 4:
      case 5: printf ("%s\n", pch);
              break;
      default: // Nothing;
    }
    pch = strtok (NULL, "|");
    iCpt++;
  }

I hope you will happy with this ;)

Answer 2

#include <iostream>
#include <string>
#include <fstream>
#include <stdio.h>
#include <sstream>
int main(int argc, char* argv[])
{  
    std::string csv_File_name = argv[1];
    std::ifstream  data(csv_File_name);
    int row_count =0 ;


    std::string line;
    while(std::getline(data,line))
    {   
        row_count +=1;

        std::stringstream  lineStream(line);
        std::string        cell;
        int column_count = 0 ;

        while(std::getline(lineStream,cell,','))
        {
            column_count+=1;
            // You have a cell!!!!
            if ( column_count == 3 || column_count == 4 || column_count == 5){
                std::cout << cell <<" row " << row_count << " column "  << column_count<< std::endl;
            }
        }
    }

}