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Class Constructor Error Help

AchyMain (16)
[Edited: 2:34pm. Changed topic name to more accurately reflect problem.]

Hi everyone,

I have a very simple program that gives a runtime error. I have identified the line where I get the error, but for the life of me, I can't figure out why I get the error. Can someone please please help me out? I will be forever grateful.

To the best of my knowledge, the contructor for a class populates a vector, but when a member function tries to access that vector, there is no data in it.

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#include<iostream>
#include<vector>
#include<ctime>

using namespace std;

class class_v {

  vector<vector <double> > vV;
public:
  class_v();
  double get_if(int, int);
  double get_mem(int, int);
};

class_v::class_v(){
  vector< vector <double> >vV;
  for (int i = 0; i<10000; i++){
    vV.push_back(vector <double> (5000, 1));
  }
  for (int i = 0; i<10000; i++){
    vV.at(i).at(0) = 0;
  }
  cout << vV.size() << endl;
}

double class_v::get_mem(int i, int j){
  return vV.at(i).at(j); // <----- the runtime error is at this line.
}

double class_v::get_if(int i, int j){
  if (j==0){
    return 0;
  }
  else{
    class_v::get_mem(i, j);
  }
}

int main() {
  class_v my_vector;
  time_t mem_start, mem_end;
  time_t if_start, if_end;
  double mem_diff, if_diff;


  time(&mem_start);
  
  for (int i = 0; i < 10000; i++ ) {
      my_vector.get_mem(i,0);
  }
   
  time(&mem_end);
  mem_diff = difftime(mem_end, mem_start);
  cout << "memory access took "<< mem_diff << endl;

  time(& if_start);
  for (int i = 0; i < 10000; i++) {
    my_vector.get_if(i, 0);
  }
       
  time(& if_end);
  if_diff = difftime(if_end, if_start);
  cout << "if took " << if_diff << endl; 

  return 0;
       
}
Last edited on
Moschops (7244)
The size of vV.at(i) is zero (examine it with cout << vV.at(i).size();) . The at function will throw an out_of_range exception if the requested position is equal to or greater than the size.

Last edited on
AchyMain (16)
Thanks for your comment. My confusion still remains: I think that I am populating vV when I call the constructor for class_v. Line 24
 
 
  cout << vV.size() << endl;
returns 10000 which means that the vector was initialized alright.

But when I try to access it again with
 
 
vV.at(0).at(0)
I get an out_of_range error, which means that vV no longer holds any data. What am I doing wrong?
AchyMain (16)
Ok, I found the problem. It is line 17, which should not be there.
Moschops (7244)
Just for completeness,

cout << vV.size() << endl;

is NOT the same as

cout << vV.at(i).size();

The first one is the size of vV, which was 10000 elements.
The second is the size of the object in the first element, which was 0.

Last edited on
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