vector of vector

[y3091hU5]

hi.i wanna define a vector of vector that have not certain member.actually i have two variable that show the rows and the columns and a third one that i want put them back into the rows and columns.how do it?

[MikeyBoy]

Your question isn't clear. Can you rephrase it to be clearer?

To define a vector of vectors of integers:

std::vector<std::vector<int>> my_vec_of_vecs;

If the nesting of template arguments is confusing, you can define types to make it clearer:

using VecOfInts = std::vector<int>;

std::vector<VecOfInts> my_vec_of_vecs;

[Grime]

Similar topic here: http://www.cplusplus.com/forum/beginner/249206/

You want to define a vector of a vector. Check. That has no members. Check. You have two variables that have the number of rows and columns. Check.

	int no_of_columns = 5, no_of_rows = 5;
	vector < vector<int> > two_d_vector = vector<vector<int> >(no_of_columns, vector<int>(no_of_rows));

Or

	int no_of_columns = 5, no_of_rows = 5;
	vector < vector<int> > two_d_vector(no_of_rows);
	two_d_vector.resize(no_of_rows, vector<int>(no_of_columns));

Or

	int no_of_columns = 5, no_of_rows = 5;
	vector < vector<int> > two_d_vector(no_of_rows);
	
	for(size_t i = 0; i < two_d_vector.size(); i++)
		two_d_vector.resize(no_of_columns);

'third one that I want put them back into the rows and columns'. What? ;-;
So you have a third variable that you want to 'put back into rows and columns' what does that mean? .-.
Can you give an example or something?

Note that you should call the vector by its indexes and not with push_back() because we had resized the vector. Otherwise you would have 5x5 of 0s (in my snippet) and then whatever you pushed back.

[y3091hU5]

dear Mikey boy and Grime
You're right. I made a mistake. It seems that what i tell is a 3D vector. Now again!
I wanna define a vector of vector with no certain member but your code have certain member. The rows and columns are known. I wanna the inner vector show the columns and outer vector show the rows that they have not certain member.
thanks.

[Grime]

My first snippet might have interchanged columns and rows. But aren't the other two what you want?

I don't get what you had meant otherwise. I thought I did. Maybe it will help us if you can post the actual question..

[Peter87]

What do you mean by "no certain member"? The type that you store in a vector need to be specified.

[y3091hU5]

may show me output of them?

[MikeyBoy]

may show me output of them?

What? What are you asking here?

I appreciate English may not be your first language, but can you try and be more clear in what you're asking for?

You can output the contents of a vector by iterating over each element of the vector, and outputing it.

Alternatively, you can use std::copy to copy the vector to std::cout .

[y3091hU5]

I mean i cant run your code. And i cant see output. I wanna to you show me output of your code.

[chicofeo]

@badoom, no one has given you any code. You need to show us your code to understand better what you mean.

[y3091hU5]

	int no_of_columns = 5, no_of_rows = 5;
	vector < vector<int> > two_d_vector(no_of_rows);
	
	for(size_t i = 0; i < two_d_vector.size(); i++)
		two_d_vector.resize(no_of_columns);

	

Yea, I mean for example in this code show me an example output. I mean with this way in a special case.

[Grime]

That snippet's wrong. two_d_vector.resize(no_of_columns); should've been two_d_vector[i].resize(no_of_columns); sorry I'm a typo king..

I don't know what kind of 'example' you were expecting. That snippet is just for reserving space and the vector is just a regular 2d vector, so you would call it like you would have with a regular vector itself.

Anyways you should be a little familiar with vectors http://www.cplusplus.com/reference/vector/vector/ and especially their methods. If you see a method like .resize() that you're not familiar with, then Google! Don't blindly copy-paste, ask yourself what a piece of code does.

As it turns out sometimes people replying can be wrong too, like I was with that post, but you should've been familiar enough that you could've spotted the error is what I'm saying.

Anyways here's an 'example' demonstrating how 'calling 2D vectors' works.

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

int main()
{
	int no_of_columns = 5, no_of_rows = 5;
	vector < vector<int> > two_d_vector(no_of_rows);

	cout << " Vector Created With 5 rows.";

	for (size_t i = 0; i < two_d_vector.size(); i++)
		two_d_vector[i].resize(no_of_columns);

	cout << "\n Vector Rows Resized To Have 5 Columns";

	for (size_t i = 0; i < two_d_vector.size(); i++)
		for (size_t j = 0; j < two_d_vector[i].size(); j++)
			two_d_vector[i][j] = 5;

	cout << "\nVector indexes filled with '5'";
	cout << "Here are vector Elements:\n";

	for (size_t i = 0; i < two_d_vector.size(); i++) {
		for (size_t j = 0; j < two_d_vector[i].size(); j++)
			cout << two_d_vector[i][j] << ' ';
		cout << '\n';
	}
	system("pause");
}

[y3091hU5]

@ Grime unfortunately it was the first time that i used a vector and i confused! But this example is really what i need.
Thanks you for your help.