Class stringstream. Cant understand how lineStream works, its parameters; - c++

Question

I have the following code, and I know how it works and what it does, however, not at all. I don't understand how these three lines work
std::stringstream lineStream(line);
std::string cell;
std::getline(lineStream, cell, ';')
Especially lineStream one;
I found them in google, but no sufficient explanation. Could you explain me please their behavior or share a good link please? Thanks in advance, have a nice day :)
container *begin = new container;
begin->beginBox = new box;
container *last = NULL;
std::ifstream data(filename);
std::string line;
std::getline(data, line);
for (container *i = begin; !data.eof() && std::getline(data, line);)
{
std::stringstream lineStream(line);
std::string cell;
std::getline(lineStream, cell, ';');
i->ID = atoi(cell.c_str());
for (box *j = i->beginBox; std::getline(lineStream, cell, ';'); j->next = new box, j = j->next)
{
j->apples = atoi(cell.c_str());
i->lastBox = j;
}
i->lastBox->next = NULL;
i->nextCont = new container(), last = i, i = i->nextCont, i->beginBox = new box;
}
setAutoIncrement(begin->ID + 1);
last->nextCont = NULL;
return begin;

Answer 1

std::stringstream lineStream(line);
This declares a variable called lineStream of type std::stringstream. It passes the line string to its constructor (2). The std::stringstream type wraps a string with a stream interface. It means you can treat it like cout and cin, using << and >> to insert and extract things from the string. Here, lineStream is being created so you can later extract its contents using std::getline.
std::string cell;
This just declares an empty std::string called cell.
std::getline(lineStream, cell, ';');
The function std::getline (1) takes a stream that it will extract a line from as its first argument. The second argument is a std::string that it will extract the line into. Without a third argument, the ending of a "line" is considered to be where we see a newline character. However, by passing a third argument, this code is making so that a line ends at ;. So this call to std::getline will extract everything from the stream up until it finds a ; character and puts that content into cell. The ; character is then discarded.
This is all very similar to the above code:
std::ifstream data(filename);
std::string line;
std::getline(data, line);
Here, the stream is a file stream instead of a string stream, and std::getline will extract everything up to a newline character because no third argument is given.