Question

My code opens a text file, counts the number of lines, allocates an array to store all lines and then calls a function to fill this array with each line. This function file.getline calls return empty strings:

Here’s the code:

typedef char* line;

…

char* filename=new char[256];
cout << "Type a file name: " << endl;
cin.ignore();
cin.getline(filename,255);

ifstream iFile(filename);

int nLines=CountLines(iFile);

line* LineArray = new line[nLines];
ReadLines(LineArray,iFile);

CountLines function:

int CountLines(ifstream &file)
{
line templine=new char[64];
int nLines=0;

while (!file.eof())
{
    file.getline(templine,64);

    if (*templine != '\n')
        nLines++;

}
delete [] templine;

return nLines;
}

This works properly. ReadLines however does not:

void ReadLines(line* LineArray, ifstream &file)
{
    line templine=new char[64];

file.seekg(0,ios::beg);

int i = 0;
while (!file.eof())
{

    if (*templine != '\n')
    {
        LineArray[i]=templine;
        i++;
    }

}
delete [] templine;
}

I have a feeling that it has something to do with the ‘\n’ issue of getline but as I set the get pointer to 0 and the file starts with normal text and not a line, I can’t understand why it fills templine with empty strings.

Answer 1

There are too many bugs in your code.

• Parameters for istream::getline() is wrong
• You need clear eof flag after CountLines()
• Wrong memory free operation.
• blah blah …

Pointers are not toys, you’d better go with Tino Didriksen’s solution.

If you really like char and pointers, it should look like this:

#include <iostream>
#include <fstream>
#include <cassert>

using namespace std;

int CountLines(ifstream &fin) {
  char templine[1024];      // no need for dynamic allocation.
  int count = 0;
  while (fin.getline(templine, 1024))
    count++;
  return count;
}

void ReadLines(char** lines, int count, ifstream &fin) {
  fin.seekg(0, ios::beg);
  for (int i = 0; i < count; i++) {
    lines[i] = new char[1024];      // you need dynamic allocation here.
    fin.getline(lines[i], 1024);
    assert(fin.gcount() < 1024);    // assure the line is shorter than 1023 chars
  }
}

int main() {

  char filename[256];         // no need for dynamic allocation.
  cin.getline(filename, 256); // second parameter should be the same size of your buffer.

  ifstream fin(filename);

  int count = CountLines(fin);
  char** lines = new char*[count];

  // After CountLines() called, fin.eof is set, you need to clear it.
  // Otherwise fin.getline() won't do a thing.
  fin.clear();
  ReadLines(lines, count, fin);

  // When every thing is done, you need to free all the memory.
  for (int i = 0; i < count; i++)
    delete[] lines[i];
  delete[] lines;

}