C++: why is vector implementation not yielding comma-delimited values? - c++

Question

I have a database.txt file with comma-separated values:
Name,ID,Year,Gender
I would like to extract each of these elements.
I've started with this code (I've already looked at all the other similar questions and implemented what they've suggested), but it's not printing each piece:
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <sstream>
using namespace std;
int main () {
string line;
ifstream myfile ("database.txt");
if (myfile.is_open())
{
while ( getline (myfile,line) )
{
std::string str = line;
std::vector<int> vect;
std::stringstream ss(str);
int i;
while (ss >> i)
{
vect.push_back(i);
if (ss.peek() == ',')
ss.ignore();
}
for (i=0; i< vect.size(); i++)
std::cout << vect.at(i)<<std::endl;
//cout << line << '\n';
}
myfile.close();
}
else cout << "Unable to open file";
return 0;
}
How can I modify it to be able to extract each value: name, ID, year, and gender? What am I doing wrong?

Answer 1

Use this function to split each line:
vector<string> split(const string &s, char delim) {
stringstream ss(s);
string item;
vector<string> tokens;
while (getline(ss, item, delim)) {
tokens.push_back(item);
}
return tokens;
}
and your code be like:
// reading a text file
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <sstream>
using namespace std;
int main () {
string line;
ifstream myfile ("database.txt");
if (myfile.is_open())
{
while ( getline (myfile,line) )
{
std::string str = line;
std::vector<string> vect;
vect = split(str, ',') ;
for (int i=0; i< vect.size(); i++)
std::cout << vect.at(i)<<std::endl;
//cout << line << '\n';
}
myfile.close();
}
else cout << "Unable to open file";
return 0;
}

Answer 2

With the help of a utility function and a data structure you can simplify this quite easily.
#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
std::vector<std::string> splitString( const std::string& stringToSplit, const std::string& delimiter, const bool keepEmpty ) {
std::vector<std::string> results;
if ( delimiter.empty() {
results.push_back( stringToSplit );
return results;
}
std::string::const_iterator itSubStrStart = stringToSplit.begin(), itSubStrEnd;
while( true ) {
itSubStrEnd = std::search( itSubStrStart, stringToSplit.end(), delimiter.begin(), delimiter.end() );
std::string temp( itSubStrStart, itSubStrEnd );
if ( keepEmpty || !temp.empty() )
results.push_back( temp );
if ( itSubStrEnd == stringToSplit.end() )
break;
itSubStrStart = itSubStrEnd + delimiter.size();
}
return results;
}
struct DataEntry {
std::string name;
unsigned id;
unsigned year;
std::string gender;
};
int main() {
std::string line;
std::fstream file;
file.open( "database.txt" );
std::vector<DataEntry> entries;
std::vector<std::string> elements;
while( file >> line ) {
elements = splitString( line, "," );
DataEntry entry;
entry.name = elements[0];
entry.id = std::stoul( elements[1] );
entry.year = std::stoul( elements[2] );
entry.gender = elements[3];
entries.push_back( entry );
}
file.close();
for ( auto& e : entries ) {
std::cout << e.name << " " << e.id << " "
<< e.year << " " << e.gender << '\n';
}
std::cout << "\nPress any key and enter to quit.\n";
std::cin.get();
return 0;
}
database.txt
John,12345,2010,M
Jane,54321,2012,F
output
John 12345 2010 M
Jane 54321 2012 F
This makes life it a lot easier just by reading in a single line first; then parsing that line of text and from there doing what you will with that data; either storing it to a struct, printing it, manipulating it etc.
Edit
You need to be aware of the fact that when reading in lines of text, and parsing them if you have something like this in your text file:
John Doe,12345,2010,M
It will not give you what you would expect. I'll leave that for you to figure out.