C++ text file based database read - c++

Question

I need simple program in C++ that will open text file and going line by line find second argument by knowing first in list.
Content of text file:
1, red
2, blue
3, green
4, orange
So I need a program that will go line by line and each line turn into array ( of two elements ) and then compare first element with user interactively inserted number.
So if user insert 2, it goes line by line, comparing first element of array-ed line and if it matches, it prints second element in array ( blue ), and if user type 3, it prints green...
I have always working in PHP, and it's much easier than this, so I am stuck a little bit with this now... :/

Answer 1

Here you go:
#include <iostream>
#include <fstream>
#include <map>
#include <sstream>
int main(int argc, char* argv[]) {
if (argc != 2) {
std::cerr << "Usage: test [inputfile]" << std::endl;
return 1;
}
std::fstream stream(argv[1]);
if (!stream.good()) {
std::cerr << "Error: could not open file: " << argv[1] << std::endl;
return 2;
}
std::string line;
std::map<int, std::string> map;
while (std::getline(stream, line)) {
std::string::size_type pos = line.find(',');
std::stringstream sstream(line.substr(0, pos));
int index;
sstream >> index;
map[index] = line.substr(pos+2);
}
int in;
while (std::cin >> in) {
std::map<int, std::string>::iterator i = map.find(in);
if (i == map.end())
std::cerr << "index not found" << std::endl;
else
std::cout << i->second << std::endl;
}
return 0;
}

Answer 2

Q1: How do you open text file in C++ ?
Q2: How do you read file line by line?
C++ Input/Output with files
Q3: How do you turn string with "," into array based on that delimiter?
How to split a string in C++?

Answer 3

This is probably not helpful, except for me; I get to practice using Spirit parsing (and karma output generation as a bonus):
#include <boost/spirit/include/karma.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/fusion/include/std_pair.hpp>
#include <fstream>
#include <map>
namespace qi = ::boost::spirit::qi;
namespace karma = ::boost::spirit::karma;
typedef std::map<int, std::string> index_t;
index_t read_index(const char* filename)
{
using boost::spirit::istream_iterator;
using namespace qi;
index_t result;
std::ifstream ifs(filename);
ifs.unsetf(std::ios::skipws);
istream_iterator begin(ifs), end;
if (!parse(begin, end, (int_ >> omit[lit(',') >> *char_(" \t")] >> *(char_ - eol)) % eol, result))
{
throw std::runtime_error("Unable to read/parse index file ");
}
return result; // http://en.wikipedia.org/wiki/Return_value_optimization
}
int main()
{
index_t index = read_index("input.txt");
using namespace karma;
std::cout << format(('[' << int_ << ": " << *char_ << ']') % eol, index) << std::endl;
for (int i=0; i<10; i++)
{
int lookup=rand()%6;
std::cout << "Random lookup: " << lookup << ": " << index[lookup] << std::endl;
}
return 0;
}
Oh, sample output:
[1: red]
[2: blue]
[3: green]
[4: orange]
Random lookup: 1: red
Random lookup: 4: orange
Random lookup: 3: green
Random lookup: 1: red
Random lookup: 5:
Random lookup: 1: red
Random lookup: 4: orange
Random lookup: 0:
Random lookup: 3: green
Random lookup: 1: red