C++ vector subscript out of range

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Hi, in the following code, I'm getting the error mentioned in the title. Here's the code:

C++

typedef struct node		// this acts as the vertex of graph
{
	string name;		// stores the unique name of the vertex
	int value;			// stores the integer data saved in the vertex
} node;

class graph
{
private:
	vector< vector<node> > adjList;		// 2D vector to store the adjencey list of the graph

public:
	graph()								// default constructor
	{
		adjList.resize(0);
	}void printBFSTrav()
	{
		stack<node> stck;
		vector<string> visited;
		vector<node> result;
		//result.resize(adjList.size());

		stck.push(adjList[0][0]);
		visited.push_back(adjList[0][0].name);

		node current;
		int i=0, vTrav=0;
		while(!stck.empty())
		{
			current = stck.top();
			result.push_back( current );
			stck.pop();

			i=0;
			for(int size=adjList.size(); i<size && adjList[0][i].name != current.name; ++i);

			for(int j=1, size=adjList[i].size(); j<size; ++j)
			{
				for(vTrav=0; (vTrav < visited.size()) && (visited[vTrav] != adjList[i][j].name); ++vTrav);

				if(vTrav!=visited.size())
					continue;

				stck.push( adjList[i][j] );
				visited.push_back( adjList[i][j].name );
			}
		}

		for(int i=0; i<result.size(); ++i)
			cout << endl << result[i].name << "(" << result[i].value << ")";  //************************
	}

I get the error when this line:

for(int size=adjList.size(); i<size mode="hold">
gets executed third time. All vector indexes are within the range AFAIK.

Posted 26-Apr-13 4:42am

Harshil Sharma

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Sergey Alexandrovich Kryukov 26-Apr-13 11:16am

Do it under the debugger. Before the exception is thrown, examine the values of all the relevant variables. You will soon find out what's wrong. That's it.
—SA

2 solutions

Solution 1

In the statement

C++

for (int size=adjList.size();
            i < size && adjList[0][i].name != current.name;
                     ++i);

you actually meant: adjList [i][0]. size is the dimension of the "outer" index, which is the first one in the notation.

Posted 26-Apr-13 6:01am

nv3

Updated 26-Apr-13 8:58am

v2

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H.Brydon · Accepted Answer · 2013-04-26T11:38:00

You are reusing a variable for 2 purposes:

C++

for(int size=adjList.size(); i < size && adjList[0][i].name != current.name; ++i)
  for(int j=1, size=adjList[i].size(); j<size; ++j) ...

The variable size is defined in the outer loop (I might add, in an unusual fashion), to apparently be the outer loop size ... then you redefine the same variable as the inner loop size. When the inner loop completes, you go to the second iteration of the outer loop, but the size value is not reset properly.

There may be other errors (I didn't look past this), but you want to move the "int size=..." outside the loops and I would suggest:

C++

int isize = adjList.size();    // defined outside the outer loop
// ...
int jsize = adjList[i].size(); // defined inside the outer loop, outside the inner loop