Reading text file per line in C++, with unknown line length - c++

Question

I have a text file, that is formatted somewhat like this:
1 3 4 5 6
6 7 8
4 12 16 17 18 19 20
20
0
A line can contain 1 to 10000 integers. What I need to do, is read all of them line by line.
Pseudocode like this:
line=0;
i=0;
while(!file.eof()){
while(!endLine){
array[0][i++]=file.readChar();
}
line++;i=0;
}
So, I have an array , into which I would like to read every line, and each line would consist of each of these integers.
The problem I'm having, is how to check if the end of a line has come.
Note, I can't use strings.
Yes, This is for a homework, but the main task for the assignment is to build a tree and then transform it. I can do that, but I've no idea how to read the integers from the file.

Answer 1

Probably something like this:
after reading an int, I manually skip spaces, tabs, carriage return and end of line (for this one you'll have to implement your logic).
To read an int I read it directly using the C++ functions of ifstream. I don't read it character by character and then recompose it as a string :-)
Note that I skip \r as "spaces. The end of line for me is \n.
#include <iostream>
#include <fstream>
#include <vector>
int main()
{
std::ifstream file("example.txt");
std::vector<std::vector<int>> ints;
bool insertNewLine = true;
int oneInt;
//The good() here is used to check the status of
//the opening of file and for the failures of
//peek() and read() (used later to skip characters).
while (file.good() && file >> oneInt)
{
if (insertNewLine)
{
std::vector<int> vc;
ints.push_back(vc);
//With C++11 you can do this instead of the push_back
//ints.emplace_back(std::vector<int>());
insertNewLine = false;
}
ints.back().push_back(oneInt);
std::cout << oneInt << " ";
int ch;
while ((ch = file.peek()) != std::char_traits<char>::eof())
{
if (ch == ' '|| ch == '\t' || ch == '\r' || ch == '\n')
{
char ch2;
if (!file.read(&ch2, 1))
{
break;
}
if (ch == '\n' && !insertNewLine)
{
std::cout << std::endl;
insertNewLine = true;
}
}
else
{
break;
}
}
}
//Here we should probably check if we exited for eof (good)
//or for other file errors (bad! bad! bad!)
return 0;
}

Answer 2

There is a function called getline() which will read a whole line. Link

Answer 3

You need a function to read a value from a file or indicates an end of line or end of file condition, something like:
result_type GetNextValue (input_file, &value)
{
if next thing in file is a number, set value and return number_type
if next thing in file is an end of line, return end_of_line_type
if end of file found, return end_of_file_type
}
and then your array building loop becomes:
line = 0
item = 0
eof = false
while (!eof)
{
switch (GetNextValue (input_file, value))
{
case value_type:
array [line][item++] = value
case end_of_line_type:
line++;
item = 0;
case end_of_file_type:
eof = true
}
}
I'll leave the details to you as it's homework.

Answer 4

You could read the numbers in a char and check against carriage return. A snippet that I had just tried is given below:
ifstream ifile;
ifile.open("a.txt");
char ch;
while((ch = ifile.get()) != EOF)
{
std::cout<<ch<<"\n";
if (ch == '\n')
std::cout<<"Got New Line";
}
ifile.close();