2D vector

tay · #1 15-Feb-2004, 05:55

anyone know how to create a 2D vector,
can give an example how to create it,
and how to inside the data inside the 2D vector
like:

1 2 3
4 5 6
7 8 9 3 column and 3 row.

thx :-)

dsmith · #2 15-Feb-2004, 07:23

Tay,

Take a look at this thread. Garth gives a great explanation on 2d arrays.

tay · #3 15-Feb-2004, 07:36

2D array i know

but i want know how to create 2D vector and also want know how to insert data inside the 2D vector.

we need include <vector>, for example

CPP / C++ / C Code:

#include <iostream>
#include <vector>
using namespace std;
int main() {
  vector<int> v;
  v.push_back(4);
  v.push_back(2);
  v.push_back(1);
  v.push_back(6);
  v.push_back(8);
  v.push_back(3);

  for (int i=0;i<6;i++)
     cout << v[i] << " "; 
}

but i no idea make it to 2D vector
can u help me dsmith

dsmith · #4 15-Feb-2004, 08:08

Quote:

Originally Posted by tay

can u help me dsmith

Tay, you have found my major weakness! I hope that someone else can help you, because I am illiterate in most of the C++ stuff.

If no one else posts, I will look into it, but I really know nothing about this...

tay · #5 16-Feb-2004, 08:56

i thought c also got vector

Garth Farley · #6 16-Feb-2004, 12:48

You can create types that contain 2 ints, like this:

CPP / C++ / C Code:

typedef struct{
int x;
int y;
} coord;

This is declared as:

CPP / C++ / C Code:

coord point;
point.x = 5;
point.y = 7;

This is a new type, which you can tell the vector class to use. See if you can figure out how you can use this via vector template.

This is C, in C++ I'd create a coord class with 2 public variables x & y (or even better, public functions which alter the private variables) which can also be used in the vector class.

GF

tay · #7 16-Feb-2004, 21:13

let say i want make 50 x 50 square
what to do it
mean column 50 , row also 50

Garth Farley · #8 17-Feb-2004, 11:18

Oh, that's a matrix. There is no premade matrix class sadly (although there's plenty on the net). But they're not hard to code, if you're well up on pointers. www.gidforums.com.

This is purely C:

CPP / C++ / C Code:

double *ptr;
int N = 10; // => N*N matrix will be created.
ptr = calloc(N*N, sizeof(double) ); //memory allocated & zeroed
if(ptr == NULL){  //whoopsee
	printf("Memory allocation failure.");
	exit(1);
}

//To set a value (i,j) in the array to 18.4
*(ptr + (i*N) + j) = 18.4;

C++ has a far nicer way of playing with matrices. You can create a Matrix object, and tell it how big to be, and set it's values easily. But it requires writing all that yourself, but it's not too tough.
GF

Garth Farley · #9 17-Feb-2004, 11:21

However, the code I've just posted doesn't do what vector can. Vector is a linked list, where you can add new links all the time. Above once you've called calloc, a chunk of memory is allocated. This won't expand dynamically without shedloads of nasty stuff, and isn't worth it. So you#ve to be sure how big you want the array before you call calloc.

Hmmm, I'm wondering if it's possible to make a vector of vectors?
GF

kzutter · #10 05-May-2004, 15:56

I see this thread is a little old, and you have probably already solved your problem, but this may help someone.

CPP / C++ / C Code:

#include <iostream>
#include <vector>
using namespace std;

int main( )
{
  // create a vector of vectors
  vector< vector< int> > v2d;

  // just a temp to populate v2d
  vector< int> row;

  // populate v2d
  for(int i = 1; i<10; i++){
    row.push_back(i);
    if( i%3 == 0){
      v2d.push_back(row);
      row.clear();
    }
  }
  // output
  for(int i=0; i<3; i++){
    for(int j=0; j<3; j++){
      cout << v2d[i][j]; // note array style indexing, but be careful! - no bounds checking
    }
    cout << endl;
  }


}

Quote:

Originally Posted by tay

anyone know how to create a 2D vector,
can give an example how to create it,
and how to inside the data inside the 2D vector
like:

1 2 3
4 5 6
7 8 9 3 column and 3 row.

thx :-)

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2D vector

2D Vector Sample