Getting input from a file

[cwarren13]

So, I'm working on a project to solve a maze thats given to it by an input file. This is for school.

I am retarded and I can't make heads or tails of the groundwork that she provided for us (starting code).

Here it is:

#include <string>
typedef struct
{
    short int doorEncoding; // Range 0..15.
            // north = doorEncoding & 0x08
            // east  = doorEncoding & 0x04
            // south = doorEncoding & 0x02
            // west  = doorEncoding & 0x01
            // Note that the result of these operations is not
            // necessarily 1, but some non-zero value if there
            // is in that particular direction. 0 else.
    bool      visited;
    int       parentRow;
    int       parentCol;
    char      direction; // From parent.
} MazeCell;

typedef struct
{
    int row;
    int col;
} CellPosition; // useful as StackItem or QueueItem.

class Maze
{
public:
    Maze(const string& fileName); // Load from file.
    void Solve(); // Solve the maze.
    void PrintSolution();
private:
    vector<vector<MazeCell> > maze; // maze square
    int rows;                        // number of rows
    int cols;                        // number of columns
    int mouseRow;                    // row position of mouse
    int mouseCol;                    // col position of mouse
    int cheeseRow;                   // row position of cheese
    int cheeseCol;                   // col position of cheese
    int squaresVisited;
};

Maze::Maze(const string& fileName):
            maze(0),   // init maze
            rows(0),
            cols(0),
            mouseRow(0),
            mouseCol(0),
            cheeseRow(0),
            cheeseCol(0),
            squaresVisited(0)
{
    // declare variable to open file etc.
    // read m and n and init rows and cols.
        // read and init mouse and cheese positions.
    // Now we know the size of maze. let us init.
    // Reserve space for rows (= n) many rows.
    maze.resize(n);
    // reserve space for cols (= n) many columns in each row.
    for (int rowNum = 0; rowNum < rows; rowNum++)
    {
        maze[rowNum].resize(cols);
    }
    // Now we can use maze[0][0] ... maze[n-1][m-1].
    // Read and initialize all the cells.
}

What I'm confused on is the last part

Specifically, what does this do?

maze(0),   // init maze
            rows(0),
            cols(0),
            mouseRow(0),
            mouseCol(0),
            cheeseRow(0),
            cheeseCol(0),
            squaresVisited(0)

Does this set everything to the default value of 0 to start off with?

And this...

   ifstream ("myfile.txt")
    std::cin >> m;

What is this doing? Anything? As far as I can tell myfile doesn't actually point to anything yet and std::cin >> m; is trying to get input from the user right?

I need to know this before I start

[sjaycohn]

Yes, the code you were asking about initializes the variables of that class.
You can only do that in the constructor though.
That is a kind of pre-initialization that occurs before the first line of the function (the constructor) is executed.
Use it if you want - I still like to initialize variables the old C way - through direct assignment, but this has its uses too, as you will see as you use it.

I hope this helps.

[sjaycohn]

As for the other piece of code:

[CODE]
ifstream ("myfile.txt")
std::cin >> m;
[\CODE]

This doesn't do anything.
This won't even compile.
I think you left out some necessary code.
I can tell you how to actually make this work and what it should do.

ifstream stands for Input File Stream - it opens a stream capable of reading input from the file of your choice - in this case "myfile.txt"

However, this is not the correct syntax to use it.
You need to declare an ifstream variable to read into, like this:

[CODE]
ifstream in("myfile.txt", ios::in);
[\CODE]

Then to read into the variable like this:

[CODE]
std::string a;
in >> a;
[\CODE]

And yes, cin gets the input from the user.


Let me know if you are still confused.