Read file (containing int, string) to vector of pairs using ifstream

Question

I'm trying to read a text file into a vector of pairs. The text file contains the following: The first line tells, how many strings there are. The second line is an int, telling how many characters there are in the (first) string. And then, the third line contains the string itself. After that, the next "pattern" follows (again with int how many characters and then string itself). For example:

2
3
ABC
4
CDEF

My idea was, to read the first line separately (which works fine). Then create pairs for each int and string. The second part, somehow, doesn't work, so I would really appreciate if someone could help me find the mistake.

So here's my code:

#include <iostream>
#include <stdlib.h>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <utility>

using namespace std;

int main(int argc, char *argv[])
{

if (argv[1]) 
{some code here...}

// arg[2] is formatted in some manner of the example above

if (argv[2])
{

//Declare Variables:
    string buffer;
    string temporary;
    vector <pair <int, string> >  patVec;
    pair <int, string> patPair;

// Ifstream first txt File = (argv[2]

        ifstream ifile2(argv[2]);

// Get first line and store in variable number of Patterns --> This works fine

        getline(ifile2, temporary);
        int numberOfPatterns = atoi(temporary.c_str());
// Process rest of file

       int i;
       for (patVec[i=0]; i <= numberOfPatterns - 1; i++)
        {
         getline(ifile2, buffer);

         stringstream strs(buffer);

 // Fill up the Vector with pairs
            strs >> patPair.first;
            strs >> patPair.second;

            patVec.push_back(patPair);
        }
    }
 }

So here's the corrected version of the relevant part, works now: Thanks for the hints;)

    //Declare Variables
    string buffer;
    string temporary;
    vector <pair <int, string> >  patVec;
    pair <int, string> patPair;
    int plength;
    string pCharacters;

    // Get first line and store in variable number of Patterns

    getline(ifile2, temporary);

    int numberOfPatterns = atoi(temporary.c_str());

    cout << "The number of Patterns is " << numberOfPatterns << endl;


    // Process rest of file

    for (int i=0; i <= numberOfPatterns - 1; i++)
    {

       // stringstream strs(buffer);

        // Fill up the Vector with pairs
        getline(ifile2, buffer);
        stringstream int_reader(buffer);
        int_reader >> plength;

        getline(ifile2, buffer);
        stringstream str_reader(buffer);
        str_reader >> pCharacters;


        patPair = make_pair (plength, pCharacters);

        patVec.push_back(patPair);

        cout << "length of pattern " << i << " is " << plength << endl;
        cout << " characters are: " << pCharacters << endl;

    }

        ifile2.close();

    }

Why don't you just drop the first and every even line thereafter? If you read all odd line text into a vector, the other values will be obvious from the length of the vector and the length of the individual strings. — nvoigt, Nov 04 '14 at 12:56
You didn't actually ask for this but... If you're using a plain text file, why store the string size?. Just read the whole line into a std::string and If you ever happen to need its's lentgh just do line.size(). You don't even have to store how many lines are there: read until EOF is reached. — The Marlboro Man, Nov 04 '14 at 12:57
some notes: 1. Please include a self-contained, reproducing example - not what you think are only the relevant parts - see http://shadow.cat/blog/matt-s-trout/show-us-the-whole-code/ ; 2. Don't do "using namespace std;" - it's a bad idea. — Shlomi Fish, Nov 04 '14 at 13:17

score 0 · Answer 1 · answered Nov 04 '14 at 13:30

Here is a corrected program. It still suffers from some issues such as:

Predeclaration of variables.
No typedef for the pair.

But it appears to work nicely.

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

int main(int argc, char * argv[])
{
    //Declare Variables:


    std::string buffer;
    std::string temporary;
    std::vector <std::pair <int, std::string> >  patVec;
    std::pair <int, std::string> patPair;

    // Ifstream first txt File = (argv[2]

    std::ifstream ifile2((const char *)(argv[2]));

    // Get first line and store in variable number of Patterns --> This works fine

    getline(ifile2, temporary);
    int numberOfPatterns = atoi(temporary.c_str());
    // Process rest of file

    for (int i = 0 ; i <= numberOfPatterns - 1; i++)
    {
        getline(ifile2, buffer);

        std::stringstream int_reader(buffer);

        // Fill up the Vector with pairs
        int_reader >> patPair.first;

        getline(ifile2, buffer);
        std::stringstream str_reader(buffer);
        str_reader >> patPair.second;

        patVec.push_back(patPair);
    }

    return 0;
}

Read file (containing int, string) to vector of pairs using ifstream

So here's the corrected version of the relevant part, works now: Thanks for the hints;)

1 Answers1