read csv string into vector C++

Question

There are many options of csv to vector, including read a csv file and and add its all data into vector in c++ however I want to something a bit above or below csv -> vector. Instead, I have a CURL function that loads csv data into a std::string in the format of

col1,col2,col3
abc,2,ghi
jkl,2,pqr

which, each row is separated by \n. How can I parse data in this given structure into a std::vector<data>

Where data would look something like

struct data
{
  std::string col1, col3;
  int col2;
};

Answer 1

If it is only parser you need to crate in your application, you can build some simple streaming recursive parser like this:

#include <cctype>
#include <cstring>
#include <vector>
#include <string>
#include <iostream>

struct data
{
  std::string col1;
  int col2;
  std::string col3;
};

std::ostream& operator<<(std::ostream& to,const data& d)
{
    to << d.col1 << ',';
    to << d.col2 << ',';
    to << d.col3;
    return to;
}

static char* skip_spaces(const char* csv)
{
  constexpr const char* WHITESPACE = "\t\n\v\f\r ";
  return const_cast<char*>( csv + std::strspn(csv,WHITESPACE) );
}


static const char* parse_csv_line(const char* csv, data& to)
{
  char* b = skip_spaces(csv);
  char* e = std::strchr(b,',');
  to.col1 = std::string(b,e);
  b = skip_spaces(e+1);
  e = std::strchr(b,',');
  to.col2 = std::strtol(b,&e,10);
  b = skip_spaces(e+1);
  e = std::strchr(b,'\n');
  if(nullptr == e) {
    e = b + std::strlen(b);
  }
  to.col3 = std::string(b,e);
  return ('\0' == *e) ? nullptr : e + 1;
}

std::vector<data> parse_csv(const char* csv)
{
  std::vector<data> ret;
  // skip header
  csv = std::strchr(csv,'\n');
  while(nullptr !=  csv) {
    data next;
    csv = parse_csv_line(csv, next);
    ret.push_back( next );
  }
  return ret;
}


int main(int argc, const char** argv)
{
  const char* CSV = "col1,col2,col3,\r\nabc,2,ghi\r\njkl,2,pqr";
  std::vector<data> parsed = parse_csv(CSV);
  for(auto d: parsed) {
    std::cout << d << std::endl;
  }
  return 0;
}

If you need something much more complex, i.e. handling errors etc use some CSV parsing library