How can I read and manipulate CSV file data in C++?


Question

Pretty self-explanatory, I tried google and got a lot of the dreaded expertsexchange, I searched here as well to no avail. An online tutorial or example would be best. Thanks guys.

1
51
1/19/2009 6:52:37 AM

Accepted Answer

If what you're really doing is manipulating a CSV file itself, Nelson's answer makes sense. However, my suspicion is that the CSV is simply an artifact of the problem you're solving. In C++, that probably means you have something like this as your data model:

struct Customer {
    int id;
    std::string first_name;
    std::string last_name;
    struct {
        std::string street;
        std::string unit;
    } address;
    char state[2];
    int zip;
};

Thus, when you're working with a collection of data, it makes sense to have std::vector<Customer> or std::set<Customer>.

With that in mind, think of your CSV handling as two operations:

// if you wanted to go nuts, you could use a forward iterator concept for both of these
class CSVReader {
public:
    CSVReader(const std::string &inputFile);
    bool hasNextLine();
    void readNextLine(std::vector<std::string> &fields);
private:
    /* secrets */
};
class CSVWriter {
public:
    CSVWriter(const std::string &outputFile);
    void writeNextLine(const std::vector<std::string> &fields);
private:
    /* more secrets */
};
void readCustomers(CSVReader &reader, std::vector<Customer> &customers);
void writeCustomers(CSVWriter &writer, const std::vector<Customer> &customers);

Read and write a single row at a time, rather than keeping a complete in-memory representation of the file itself. There are a few obvious benefits:

  1. Your data is represented in a form that makes sense for your problem (customers), rather than the current solution (CSV files).
  2. You can trivially add adapters for other data formats, such as bulk SQL import/export, Excel/OO spreadsheet files, or even an HTML <table> rendering.
  3. Your memory footprint is likely to be smaller (depends on relative sizeof(Customer) vs. the number of bytes in a single row).
  4. CSVReader and CSVWriter can be reused as the basis for an in-memory model (such as Nelson's) without loss of performance or functionality. The converse is not true.
9
1/6/2009 5:41:55 AM

More information would be useful.

But the simplest form:

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

int main()
{
    std::ifstream  data("plop.csv");

    std::string line;
    while(std::getline(data,line))
    {
        std::stringstream  lineStream(line);
        std::string        cell;
        while(std::getline(lineStream,cell,','))
        {
            // You have a cell!!!!
        }
    }
 }

Also see this question: CSV parser in C++


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