CODEWITHSUNDEEP
c++arraysvector
12vi6
12vi6

Reputation: 50

2D array error: Vector index beyond memory allocation

can someone help me understand why i'm getting this error.

I have a file with numbers 5 4
9 1 5 3
14 12 3 10
9 7 10 14
8 5 0 3
14 13 6 14
8 11

I am adding these numbers to a 2D vector:

 25 bool function(const char* myfile){
 26 
 27   std::vector< std::vector<int> > data;
 28 
 29   std::ifstream file(myfile);
 30   std::string line;
 31 
 32   while(std::getline(file, line)){
 33     std::vector<int> lineData;
 34     std::stringstream linestream(line);
 35 
 36     int value;
 37     while(linestream >> value)
 38     {
 39       lineData.push_back(value);
 40     }
 41     data.push_back(lineData);
 42   }
 43 
 44   int i, j = 0;
 45   int vertexSize = 0;
 46   std::vector< std::vector<int> >::iterator row;
 47   std::vector<int>::iterator col;
 48   for( row = data.begin(); row != data.end(); row++, i++){
 49     for(col = row->begin(); col!= row->end(); col++){
 50       std::cout << *col << " ";
 51     }
 52     std::cout << "\n";
 53   }
 54 
 55    vertexSize = data[0][0] * data[0][1];
 56    start = data[i-1][0];
 57    goal = data[i-1][1];
 58 
 59    std::cout << "Vertex Size:" << vertexSize << "\n";
 60    std::cout << "Start: " << start << " goal:" << goal << "\n";
 61   return true;
 62 }

When i try to get the last 2 numbers in the last line, i am getting the error:

5 4 
9 1 5 3 
14 12 3 10 
9 7 10 14 
8 5 0 3 
14 13 6 14 
8 11 
Vertex Size:20
Start: 8 goal:7
** Vector<T>::operator[] error: vector index beyond memory allocation!
   Unable to recover, no memory allocated
   Terminating program

std::cout << data[i-1].size(); Shows 2 elements, which is what I am expecting, yet it is still giving me that index beyond memory allocation error for goal.

It seems that if i go beyond data[number][0], that is when the errors occur. Can someone explain to me why that is happening?

Thank you for your help.

Debugging with gdb:

warning: no loadable sections found in added symbol-file system-supplied DSO at 0x2aaaaaaab000
5 4 
9 1 5 3 
14 12 3 10 
9 7 10 14 
8 5 0 3 
14 13 6 14 
8 11 
0 0
Vertex Size:20
Start: 8 goal:7
** Vector<T>::operator[] error: vector index beyond memory allocation!
   Unable to recover, no memory allocated
   Terminating program

Program exited with code 01.
(gdb) backtrace
No stack.

Upvotes: 0

Views: 184

Answers (1)

PaulMcKenzie
PaulMcKenzie

Reputation: 35440

The issue that I see is that i is not initialized here:

int i, j = 0;

You initialized j, but not i. So later on when you use i, the value is unpredictable.

The solution of course is to do this:

int i = 0; int j = 0;

But as my comment suggested to you, don't use extraneous variables for counting, or to get the last element in a vector. If the vector is not empty, then the vector::back() function returns a reference to the last item in a vector.

Upvotes: 1

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