2D vector function

[jasonSung]

I am trying to pass a vector to a function and the function print out the vector to the console window.

#include <iostream>
#include <vector>

using std::cout;
using std::endl;
using std::vector;

void ProcessInput(const char *, vector<vector<int>> *);

int main()
{
  char inCharArry[100];
  int iRow = 5;
  int iCol = 5;
  vector<vector<int>> inVec(iRow, vector<int>(iCol));

  for (int i = 0; i < inVec.size(); ++i){
	  for (int j  = 0; j < inVec[i].size(); ++j){
		  inVec[i][j] = 1;
	  }
  }


  cout << "Calling   function ProcessInput()" << endl;
  ProcessInput(inCharArry, &inVec);
  cout << "Back from function ProcessInput()" << endl;

  return 0;
}	

void ProcessInput(const char inChar[], vector<vector<int>> *invector)
{
using namespace std;

	for(int i = 0; i < invector->size(); ++i){
		for(int j = 0; j < invector[i]->size(); ++j){
			
		}
		
	}
  cout<< "In function ProcessInput()" << endl;
}

I got an error : error c2819: type 'std::vector<_Ty>'does not have an overloaded member 'operator->'

Any help would be appreciated. Thank you so much in advance.

[Mythios]

void ProcessInput(const char inChar[], vector<vector<int>> *invector)
{
using namespace std;

	for(int i = 0; i < invector->size(); ++i){
		for(int j = 0; j < invector[i].size(); ++j){
			
		}
		
	}
  cout<< "In function ProcessInput()" << endl;
}

This looks really odd - anyway - vector<vector<int>> *invector <int> you didn't declare as a pointer so no need for the arrow '->' use the dot '.'

[Disch]

careful:

for(int j = 0; j < invector[i].size(); ++j){

That is not doing what you think. invector is a pointer (to a vector<vector>) so 'i' is not indexing your vector as you are trying to do... instead, it's indexing the POINTER (ie: accessing invalid/nonexistant objects)

This would actually need to be for(int j = 0; j < (*invector)[i].size(); ++j){


OR you could make your life easier / less error prone and pass by reference instead of by pointer:

void ProcessInput(const char inChar[], vector<vector<int> >& invector)
{
  for(int i = 0; i < invector.size(); ++i)
  {
    for(int j = 0; j < invector[i].size(); ++j)
    {
      // much better
    }
  }
}

[jasonSung]

Thank you so much for quick response.

i forgot to add one more line.

Here is what i wanna do.

1. make a 2d vector with ones and zeros in main().
2. pass this vector to a function.
3. print this vector to console window.

This is the full code

#include <iostream>
#include <vector>

using std::cout;
using std::endl;
using std::vector;

void ProcessInput(const char *, vector<vector<int>> *);

int main()
{
  char inCharArry[100];
  int iRow = 5;
  int iCol = 5;
  vector<vector<int>> inVec(iRow, vector<int>(iCol));

  for (int i = 0; i < inVec.size(); ++i){
	  for (int j  = 0; j < inVec[i].size(); ++j){
		  inVec[i][j] = iRow;
	  }
  }


  cout << "Calling   function ProcessInput()" << endl;
  ProcessInput(inCharArry, &inVec);
  cout << "Back from function ProcessInput()" << endl;

  return 0;
}	

void ProcessInput(const char inChar[], vector<vector<int>> *invector)
{
using namespace std;

	for(int i = 0; i < invector->size(); ++i){
		for(int j = 0; j < invector[i].size(); ++j){
			cout << invector[i][j] << " ";
		}
		cout << endl;
	}
  cout<< "In function ProcessInput()" << endl;
}

I got an error at line 38; error c2679: binary '<<' : no operator found which takes a right-hand operand of type 'std::vector<_Ty>'

[Disch]

see my post.

for(int j = 0; j < invector[i].size(); ++j){

This does not do as you expect


cout << invector[i][j] << " ";

neither does this. invector[i][j] is not an integer from the vector, it's a vector

invector is type vector< vector<int> >*

invector[i] is type vector< vector<int> >

invector[i][j] is type vector<int>

Pass this vector by reference instead of by pointer.

[jasonSung]

You are awesome. The following code works.

#include <iostream>
#include <vector>

using std::cout;
using std::endl;
using std::vector;

void ProcessInput(const char *, vector<vector<int>> invector);

int main()
{
  char inCharArry[100];
  int iRow = 5;
  int iCol = 5;
  vector<vector<int>> inVec(iRow, vector<int>(iCol));

  for (int i = 0; i < inVec.size(); ++i){
	  for (int j  = 0; j < inVec[i].size(); ++j){
		  inVec[i][j] = iRow;
	  }
  }

  cout << "Calling   function ProcessInput()" << endl;
  ProcessInput(inCharArry, inVec);
  cout << "Back from function ProcessInput()" << endl;

  return 0;
}	

void ProcessInput(const char inChar[], vector<vector<int>> invector)
{
using namespace std;

vector<vector<int>> ivTemp = invector;

	for(int i = 0; i < invector.size(); ++i){
		for(int j = 0; j < invector[i].size(); ++j){
			cout << invector[i][j] << " ";
		}
		cout << endl;
	}
  cout<< "In function ProcessInput()" << endl;
}

But i have one more question.

As I mentioned above, I need to do
1. read text data, which is actually adjacency list representing a graph.
2. store the graph representations with zeros and ones (zero means there is no edge, one means there is an edge) to a certain data structure.

In that case, is 2D vector a good approach? I could do it with Matlab and it wasnt that difficult but with c++ it is a different story. Any suggestion would be appreciated!

[Disch]

eek! now you're passing by value!

no no, pass by reference (or even in this case const reference because you're not changing invector)

void ProcessInput(const char inChar[], const vector<vector<int> >& invector)

notice the & symbol.

Also why are you making a copy of the vector (ivTemp)?


Anyway, as for whether or not it's a good approach. That depends on who you ask. Personally I'm not a fan of using 2D anything for gridlike structures. I wrote a biased article on the subject here: http://cplusplus.com/forum/articles/17108/