Question

I’m trying to load each line from a file in to a 2D string vector, but I keep getting a segmentation fault. Can someone show me what’s going wrong? Thanks in advance.

Printing lcount was just a way to verify that all lines were loaded (190k lines).

#include <iostream>
#include <string>
#include <fstream>
#include <vector>
using namespace std;

int loadVector(ifstream& fh, vector< vector<string> >& v);

int main(int argc, char *argv[])
{
   ifstream fh1(argv[1]);
   ifstream fh2(argv[2]);

   vector< vector<string> > v1;
   vector< vector<string> > v2;

   int v1_lines = loadVector(fh1, v1);
   int v2_lines = loadVector(fh2, v2);

   cout << "v1: " << v1_lines << "\n";
   cout << "v2: " << v2_lines << "\n";
}

int loadVector(ifstream& fh, vector< vector<string> >& v){
   int lcount = 0;
   while (fh.good() && fh){
      string line = "";
      getline(fh, line);
      v[lcount].push_back(line);
      ++lcount;
   }
   fh.close();
   return lcount+1;
}

Answer 1

The line:

 v[lcount].push_back(line);

will seg fault because you’re accessing v[lcount] before putting any vector elements into vector v. Do v.push_back(vector()) to give that element a vector, and then fill in the inner vector with the line above.

Remember, it’s a vector of vectors. The first vector contains vectors, but if it doesn’t contain any yet then accessing its [0]’th element is undefined behavior because you’re accessing uninitialized memory. The [0]th element only exists once you’ve pushed an element (your 2nd dimension vector) into it the first time.

PS: I don’t think you need a 2-d vector here, you can just do a vector of strings from the look of it.