Read file and input into vector - c++

Question

Given a text file with the following fixed contents (only two lines, nothing more):
43 65 123 13 41
83 67 22
I need it to turn into a vector array where I can apply the name.size() to find out the length of the array and also to make use of the integers inside for other purposes.
The result should be:
Array 1: 43 65 123 13 41
Array 2: 83 67 22
Array 1 Length: 5
Array 2 Length: 3
I have successfully read the text file and added the content using .push_back(). However when I cout the vector .size(), it returns 2 and I realised that it consider each line as an element in the array.
What is the approach to tackling this?
Edit:
Added snippet of the code:
vector <string> readFile(const string& fileName)
{
ifstream source;
source.open(filename);
vector <string> lines;
string line;
while(getline(source, line)
{
lines.push_back(line);
} return lines;
}
int main(int argc, char ** argv)
{
string inputFile(argv[1]);
vector <string> fileData = readFile(inputFile);
// Check vector
for(auto i : fileData)
cout << i << endl;
// Check vector length
cout << fileData.size() << endl;
}

Answer 1

As already mentioned, std::getline and std::istringstream are good starting points.
Then you can use std::istream_iterator to create the vectors directly using the iterator overload of the std::vector constructor.
Perhaps something like this:
std::vector<std::vector<int>> read_file(std::istream& input)
{
std::vector<std::vector<int>> lines;
std::string line;
while (std::getline(input, line))
{
std::istringstream line_stream(line);
lines.emplace_back(std::istream_iterator<int>(line_stream),
std::istream_iterator<int>());
}
return lines;
}
This handles an arbitrary number of lines containing an arbitrary number of integer values.
Can be used something like this:
int main(int, char* argv[])
{
std::ifstream input(argv[1]);
auto data = read_file(input);
std::cout << "First line of data: ";
for (auto value : data[0])
{
std::cout << value << ' ';
}
std::cout << '\n';
std::cout << "Second line of data: ";
for (auto value : data[1])
{
std::cout << value << ' ';
}
std::cout << '\n';
}
Important note: The example above lacks any kind of error or range checking. It's left as an exercise for the reader.

Answer 2

You could read each one as a text line, then extract the numbers from the text.
std::vector<std::vector<int>> database;
std::string text_line;
while (std::getline(cin, text_line))
{
std::vector<int> numbers_row;
std::istringstream number_stream(text_line);
int value;
while (number_stream >> value)
{
numbers_row.push_back(value);
}
database.push_back(numbers_row);
}
The inner loop creates a vector based on the numbers in that text line.
The outer loop creates vectors and appends them to the database.

Answer 3

The common way is to use std::getline to read line by line, to put it in a std::istringstream and then to use formatted input from that stream - but you've already gotten answers for that so I'll throw in an alternative.
This uses formatted input directly from the ifstream (or any istream descendant) and peek()s to see if a newline (\n) is the next character.
It could look like this:
#include <istream>
#include <vector>
std::vector<std::vector<int>> read_stream(std::istream& is) {
std::vector<std::vector<int>> res;
std::vector<int> cur;
int x;
while(true) {
if(is.peek() == '\n') {
// save what we've gotten on the current line
res.emplace_back(std::move(cur));
cur.clear();
}
if(is >> x) cur.push_back(x);
else break;
}
return res;
}