Error when attempting to input strings into dynamically allocated array

Question

I'm trying to code the following program to read a single word per line from a text document, then print the same words to another text document, but for some reason I am encountering a rather large error after adding in:

for(int i = 0; i < num_lines; i++)
{
    getline (myfile_in, line);
    stringstream(line) >> arr[i];
}

Im not sure why this is causing an error because I copied this loop from a program that I wrote previously. The error goes away once i remove the stringstream line, but as far as I'm aware, I need it in order to copy the contents over to the array. Any help would be greatly appreciated :)

#include <fstream>
#include <string>
#include <sstream>
#include <assert.h>

using namespace std;

int main(void)
{   
ifstream myfile_in;
myfile_in.open ("words_in.txt");
ofstream myfile_out;
myfile_out.open ("words_out.txt");

string line;
int num_lines = 0;
string *arr;

assert (!myfile_in.fail());
myfile_in >> line;

while (!myfile_in.eof())
{
    getline (myfile_in, line);
    num_lines++;
}

arr = new string[num_lines];

for(int i = 0; i < num_lines; i++)
{
    getline (myfile_in, line);
    stringstream(line) >> arr[i];
}

for(int i = 0; i < num_lines; i++)
{
    myfile_out << arr[i] << endl;
}

myfile_in.close();
myfile_out.close();
return 0;
}

while (!myfile_in.eof()) I believe you will read past the end of the file this way — SingerOfTheFall
– SingerOfTheFall, Commented Oct 15, 2015 at 7:53
Why aren't you using arr[i] = line or arr[i] = string(line) ? — malhotraprateek
– malhotraprateek, Commented Oct 15, 2015 at 7:57
@malhotraprateek shouldn't stringstream(line) >> arr[i] accomplish a similar thing? — Caleb Moriarty
– Caleb Moriarty, Commented Oct 15, 2015 at 8:03
Dont know :P never used that but it seems a tad complicated... — malhotraprateek
– malhotraprateek, Commented Oct 15, 2015 at 8:06

yzn-pku · Accepted Answer · 2015-10-15 07:51:49Z

1

Why not getline (myfile_in, arr[i]); ?

answered Oct 15, 2015 at 7:51

yzn-pku

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8 Comments

Caleb Moriarty Over a year ago

I just tried that, it doesn't crash when compiling, but it just prints blank lines in the output file.

yzn-pku Over a year ago

@CalebMoriarty That's because in while (!myfile_in.eof()) loop you had read all lines in the file. If you need to read them again, you can try reopening the file.

yzn-pku Over a year ago

@CalebMoriarty And I believe using a std::vector may be a better solution in your problem.

Caleb Moriarty Over a year ago

Im sure it would be, but I haven't learned about that in class yet haha.

yzn-pku Over a year ago

@CalebMoriarty lol. The solution is simple, add myfile_in.seekg(0) right after the while loop.

|

FedyuninV · Accepted Answer · 2015-10-15 08:03:10Z

1

Probably, after while loop you've already read whole file. And then in for loop you again trying to readline from this stream. I think, you should remove readline command from for loop.

answered Oct 15, 2015 at 8:03

FedyuninV

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