vector<vector<T> > ?

This is a discussion on vector<vector<T> > ? within the C++ Programming forums, part of the General Programming Boards category; vector<vector<T> > is kinda like 2D, right? How would I insert something to it? I know how to do it ...

  1. #1
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    vector<vector<T> > ?

    vector<vector<T> > is kinda like 2D, right? How would I insert something to it? I know how to do it with vector<T> but my brains seem to sprain when figuring this one out (perhaps 'cause this was the very first day when I did something with STL).
    kooma - t.h@iki.fi

  2. #2
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    You could do something like -

    Code:
    #include <iostream>
    #include <vector>
    
    using namespace std;
    
    
    int main ( void )
    {
    	vector<vector<int> > i;
    
    	vector <int> temp1;
    	temp1.push_back(1);
    	temp1.push_back(2);
    	vector <int> temp2;
    	temp2.push_back(3);
    	temp2.push_back(4);
    
    	i.push_back(temp1);
    	i.push_back(temp2);
    
    	cout << i[0][0] << i[0][1] << i[1][0] << i[1][1];
    	
    	
    	return 0;
    
    }

  3. #3
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    This is probably clearer, as long as you note that the inner vectors are limited to a size of 20 -

    Code:
    #include <iostream>
    #include <vector>
    
    using namespace std;
    
    
    int main ( void )
    {
    	vector<vector<int> > i;
    
    	vector <int> temp1(20);
    	i.push_back(temp1);
    	i.push_back(temp1);
    	i[0][0] = 1;
    	i[0][1] = 2;
    	i[1][0] = 3;
    	i[1][1] = 4;
    
    
    
    	cout << i[0][0] << i[0][1] << i[1][0] << i[1][1];
    
    
    	
    	
    	return 0;
    
    }
    Although you could resize the inner vectors doing -

    i[0].resize(30);

    or dynamically push elements on the back using

    i[0].push_back(21);

    which would then be accessed like -

    cout << i[0][20];

  4. #4
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    Just what I figured out an hour later after posting... :-) But, what I was after was how to do it without that temp variable; is it possible to hardcode that temp1 in?
    kooma - t.h@iki.fi

  5. #5
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    Code:
    #include <vector>
    
    using std::vector;
    
    int main() {
        int width = 10;
        int height = 10;
    
        // Create a vector of width vectors of height ints
        vector<vector<int> > vecvec(width, vector<int>(height));
    }
    Note that moving a vector is expensive so compound containers will be quite inefficent (the STL thinks of a move as a copy followed by the destruction of the source, see Typed Buffers at www.moderncppdesign.com for a workaround).
    - lmov

  6. #6
    Confused Magos's Avatar
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    Ummmmm?

    Ummm, I have never seen that syntax before: vector<vector<int>> i
    What does it do? Whats the differens from int i[?][?]?
    MagosX.com

    Give a man a fish and you feed him for a day.
    Teach a man to fish and you feed him for a lifetime.

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