LinuxQuestions.org - why am i getting a segmentation fault in c++ when i am just copying vectors?

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why am i getting a segmentation fault in c++ when i am just copying vectors?

This is really weird. If you look at the bolded line, that is the one causing the segmentation fault. What I am trying to do in this program is take in a text file with about 100 lines of text and separate them into words. I need to get a vector with all the words in them so I can then count how many of each word appears....any help is appreciated. Thanks!!!!!

#include <fstream> /
#include <sstream>
#include <string>
#include <iomanip>
#include <cstring>
#include <iostream>
#include <vector>

using namespace std;

int main(int argc, char* argv[])
{
ifstream datafile;
char filename[80];
cout << "Enter file: ";
cin >> filename;
string line;

datafile.open(filename);
if (datafile.is_open());
{

while (! datafile.eof())
{

vector<string> tokens;
getline (datafile, line);
vector<string> returned_strings;
char* current_token =strtok(const_cast<char*>(line.c_str()), " ");

while (current_token != NULL)
{
returned_strings.push_back(string(current_token));
current_token = strtok(NULL, " ");
}

for (int i = 0; i < returned_strings.size(); ++i)
{
cout << returned_strings[i] << endl;
tokens[i]=returned_strings[i];

}

}

datafile.close();
}

return 0;
}

why not use the old fashion char *

Quote:

Originally Posted by Clarislock (Post 3702088)

the bolded line, that is the one causing the segmentation fault.

Vectors don't work that way.
tokens[i] is only valid if the vector is already big enough that element i exists. If the vector is not big enough, that usage does not extend the vector, it seg faults (as you have observed).

Hello.

1.

Code:

vector<string> tokens;

You are not providing an initial "capacity" parameter to the constructor. You should be using push_back(). Oddly enough, you do this for returned_strings..

2. Why not use tokens = returned_strings ?

3. tokens is not used until -after- returned_strings is "filled", and the two vectors appear to have the same scope. Why not postpone the definition and then use a copy constructor?

4. Here is something hastily adapted from some code pieces present in "The C++ Programming Language - 3rd edition" [Bjarne Stroustrup]:

Code:

#include <algorithm>

#include <fstream>

#include <iostream>

#include <iterator>

#include <map>





std::map<std::string, int> histogram;





void record(const std::string &s)

{

        histogram[s]++;

}



void print(const std::pair<const std::string, int> &r)

{

        std::cout << r.first << ' ' << r.second << '\n';

}



int main()

{

        std::ifstream is("data.in");

        std::istream_iterator<std::string> ii(is);

        std::istream_iterator<std::string> eos;



        for_each(ii, eos, record);

        for_each(histogram.begin(), histogram.end(), print);

}

Does it do what you need? The above mentioned book is pretty instructive, consider reading it.