Example
In the example below we use std::string and operator>> to read items from the file.
std::ifstream file("file3.txt");
std::vector<std::string> v;
std::string s;
while(file >> s) // keep reading until we run out
{
v.push_back(s);
}
In the above example we are simply iterating through the file reading one "item" at a time using operator>>. This same affect can be achieved using the std::istream_iterator which is an input iterator that reads one "item" at a time from the stream. Also most containers can be constructed using two iterators so we can simplify the above code to:
std::ifstream file("file3.txt");
std::vector<std::string> v(std::istream_iterator<std::string>{file},
std::istream_iterator<std::string>{});
We can extend this to read any object types we like by simply specifying the object we want to read as the template parameter to the std::istream_iterator. Thus we can simply extend the above to read lines (rather than words) like this:
// Unfortunately there is no built in type that reads line using >>
// So here we build a simple helper class to do it. That will convert
// back to a string when used in string context.
struct Line
{
// Store data here
std::string data;
// Convert object to string
operator std::string const&() const {return data;}
// Read a line from a stream.
friend std::istream& operator>>(std::istream& stream, Line& line)
{
return std::getline(stream, line.data);
}
};
std::ifstream file("file3.txt");
// Read the lines of a file into a container.
std::vector<std::string> v(std::istream_iterator<Line>{file},
std::istream_iterator<Line>{});
