cout string and vector in the same line

Question

Whenever I put a string and a vector in the same line, the string becomes empty. In my code I have,

string line, s1, s2; 
vector<pair<string,int> > binaryvector;
ifstream filename(uncompr_filename.c_str());

If I do

while(getline(filename, line))
{
    s1 = line.c_str();
    s2 = binaryvector[0].first.c_str();
    cout << s1 << endl;
    cout << s2 << endl;
}

it prints both the values of s1 and s2. But if I do,

while(getline(filename, line))
{
    s1 = line.c_str();
    s2 = binaryvector[0].first.c_str();
    cout << s1 << s2 << endl;
}

it prints just the s2 string. Where am I going wrong? This is just to illustrate the problem. What I am actually trying to do is to compare s1 and s2 using if(s1 == s2). But if I do that it returns false because s1 does not seem to have anything and is not equal to the s2 string.

Complete Code.

#include <iostream>
#include <fstream>
#include <algorithm>
#include <string>
#include <map>
#include <vector>
#define DICTIONARYSIZE 4

using namespace std;
typedef map<string,int> Instruction_Binaries;
struct val_greaterthan : binary_function < pair<string,int>, pair<string,int>, bool >
{
        bool operator() (const pair<string,int>& x, const pair<string,int>& y) const
        {return x.second > y.second;}
}val_gt;

int main(int argc, char *argv[])
{
    int c, i;
    Instruction_Binaries binary_count;
    string uncompr_filename, compr_filename, outfilename;

        if(argc <= 3)
        {
                cout << "Format is \"./SIM -c original.txt cout.txt\" or \"./SIM -d compressed.txt dout.txt\"" << endl;
                return 1;
        }
    while ((c = getopt (argc, argv, "c:d:")) != -1)
        switch (c)
        {
                case 'c':
                        (uncompr_filename=optarg);
                        break;
                case 'd':
                        (compr_filename=optarg);
                        break;
                default:
                        cout << "Format is \"./SIM -c original.txt cout.txt\" or \"./SIM -d compressed.txt dout.txt\"" << endl;
                        abort ();
                        break;
        }

    ifstream ifile(uncompr_filename.c_str());
    string binary, Directory_Index;

    while (ifile >> binary){
        int index;
        ++binary_count[binary];
    }

    vector<pair<string,int> > binaryvector;
    copy(binary_count.begin(), binary_count.end(), back_inserter(binaryvector));
    sort(binaryvector.begin(), binaryvector.end(), val_gt);

    while(ifile >> binary){
        int flag = 0;
        for(i=0; i<4; ++i){
                if(i==0) Directory_Index = "00";
                else if(i==1) Directory_Index = "01";
                else if(i==2) Directory_Index = "10";
                else if(i==3) Directory_Index = "11";
                if(binary == binaryvector[i].first){
                        cout << "001" << Directory_Index << endl;
                        flag=1;
                        break;
                }
        }
    if(flag == 0)
                cout << binary << endl;
    }
    return 0;
}

Answer 1

The problem is somewhere else in your code, as this works:

#include <iostream>
#include <vector>
#include <string>
#include <utility>
#include <fstream>

using namespace std;

int main()
{
    string line, s1, s2; 
    vector<pair<string,int> > binaryvector;
    binaryvector.push_back({"heya", 5});
    ifstream filename("input.txt");

    while(getline(filename, line))
    {
        s1 = line.c_str();
        s2 = binaryvector[0].first.c_str();
        cout << s1 << s2 << endl;
    }
    return 0;
}

I ran this over on http://www.compileonline.com/compile_cpp11_online.php with an input file that looked like this:

This is the file you can use to provide input to your program and later on open it inside your program to process the input.
second line
third line

After a blank line!  Booya!
and a line without "ending" it

The output looked like this:

This is the file you can use to provide input to your program and later on open it inside your program to process the input.
heya
second line
heya
third line
heya
heya
After a blank line! Booya!
heya
and a line without "ending" itheya

This means that there is no problem with cout, but you're doing something else horribly wrong somewhere, since the "minimal" program I just made works 100% with your "constrained" problem.