vectors?

[nikman]

int loadCarts(string filename,SnackCart *&carts) {
	carts = new SnackCart;
  ifstream dataFile(filename.c_str());
  int count = 0;
  string type;
  getline(dataFile,type);
  while (!dataFile.eof()) {
	  if (type == "Snackcart"){
	string owner;
    getline(dataFile,owner);
    if (owner == "") {
      break; // stop read if reach end of file
    } else {
      carts[count].setOwner(owner);
      string location;
      getline(dataFile,location);
      carts[count].setLocation(location);
      carts[count].clearMeals();
      bool moreMeals = true;
      while (moreMeals) {
        string meal;
        getline(dataFile,meal);
        if (meal == "#") { 
          moreMeals = false;
        } else {
          string numStr;
          getline(dataFile,numStr);
          float num = (float) atof(numStr.c_str());
          string ratingStr;
          getline(dataFile,ratingStr);
          carts[count].addMeal(meal,num,ratingStr);
        }
	  }
    }
  }
	++count;

  }
  dataFile.close();

i have the above function and i know what exactly is wrong with it. this function is used to read snackcarts from a text file. the problem is since i dont know how many snackcarts are present in the text file, i end up with errors. carts is dynamically declared but at the moment it can take only one set of values for one cart. how do i set the size of the array in this case? im guessing i can use vectors but even after reading up on it im still unsure of how to implement them.

thanks :)

[firedraco]

Well, carts = new SnackCart; creates a single snackcart (not an array). If you haven't read this:

http://www.cplusplus.com/reference/stl/vector/

Do it first. If you have, what exactly about std::vector is confusing you?

[nikman]

i want to know how to resize the vector and in such a way that the array is only equal to the size it needs to be. how about if i keep a count value that increments itself as the vector is filled and then the final count value i use to resize the vector. will that do the trick?

[jsmith]

You should start with an empty vector (vector containing 0 elements) and use the push_back() method to
add elements to it. In this way, when you are done, the vector will be exactly as large as you wanted it.

[nikman]

so can i do the following? :

string abc;
getline(dataFile, abc);
give the arguement vector.push_back(abc);

also if i create a vector of my own created datatype will it be considered a dynamic object because vectors are dynamic arrays?

[TaikoDragon]

no a vector is a template type meaning that for each input type there is created a version of the vector template. so your std::vector<SnackCart> is not a real type and can be treated like you would any normal stack variable.

Also pushing into the vector would look like..

vector<SnackCart> carts;
SnackCart thisCart;
carts.push_back(thisCart);

There is now a copy of thisCart in carts... the internal handling of memory by the vector is not something you need to consider or understand in order to use it; however in time I would say you'll need to understand how it manages itself internally to make usage of it more efficient.

[nikman]

i get it. but can i use a pointer in this case?

vector<SnackCart> carts;
SnackCart *thisCart;
carts.push_back(thisCart);

[JCED]

In that case, you must declare the vector as vector<SnackCart*> carts; OR you must add the element like this: carts.push_back(*thisCart);.

[nikman]

ok thanks :)