Resizing a Dynamic Memory Array

[scottwuzhear]

I've finally told myself that I'm going to learn C++, so I've been using the tutorials on the site, and they're great. I've run into just one problem that I can't seem to find an answer for:

If I create an array using dynamic memory:

string * line;
line = new string [1];

How can I extend the size of the array while keeping the contents I store in line[0]?

Specifically, my code is:

	int x = 0;
	string * line;
	
	ifstream file(FILENAME);
	if(file.is_open())
	{
		while(!file.eof())
		{
			line = new string [++x];
			getline(file, line[x-1]);
		}
		file.close();
		for(int a=0;a<x;a++)
		{
			cout << line[a] << endl;
		}
	}                                                                 

I want to be able to keep resizing the array to be just as large as I need. I'm aware that I could get the size of the file before reading in the lines. I'm just picky and want to know how to do it this way.

Thanks!

[jsmith]

Use an STL container such as vector<> or deque<> instead. (Ultimately these classes do exactly what you are asking anyway; they just keep you from having to worry about the details).

[scottwuzhear]

Thanks for the quick reply! Wow, the vector<> container is pwn. Here is my code now:

int main()
{
	vector<string> line;
	string tmp;

	ifstream file(FILENAME);
	if(file.is_open())
	{
		while(!file.eof())
		{
			getline(file, tmp);
			line.push_back(tmp);
		}
		file.close();
		
		for(int a=0;a<line.size();a++)
		{
			cout << line.at(a) << endl;
		}
	}
	else cout << "Error: Could not open file.";
	return 0;
}                                                                  

One last question:

How could I rewrite this so that I don't have to use the tmp string variable to get the input into the vector.pushback() method?

[firedraco]

I don't think you can. (At least I haven't found a way).

[scottwuzhear]

Thanks. After I thought about it for a bit, I agree.

[jsmith]

Well, you could

line.push_back( string() );
getline( file, line.back() );

or you could write your own wrapper:

string my_getline( ifstream& file ) {
    string tmp;
    getline( file, tmp );
    return tmp;
}

// ...
line.push_back( my_getline( file ) );

Neither of which buys you much....