CODEWITHSUNDEEP
c++stl
Tushar
Tushar

Reputation: 97

Printing graph from Input file

int main()
{

char line[100];
int N = 5;
vector<int>adj[N];
FILE *in = fopen("test.txt", "r");

for (int i = 1; i <= N; i++)
{
    fgets(line, 100, in);

    char *pch = strtok(line, "\t \n");
    int u = atoi(pch);

    pch = strtok(NULL, "\t \n");
    while (pch != NULL)
    {
        int v = atoi(pch);
        adj[u].push_back(v);
        pch = strtok(NULL, "\t \n");
    }

}
    for( int i = 0 ; i < 5; i++ )   // Printing graph
    {
       for( int p = 0 ; p < adj[i].size(); p++ )
       {
            cout<< i << " , "<< adj[i][p]<<endl;
        }
    }

Here "test.txt" file contains the data like this 

1 2 3
2 1 4 5
3 1
4 2 
5 2

First column contains the vertices ( 1 - 5 ) 

1 2 3

Above row ( first row ) means , Node 1 is connected to Node 2 and Node 3 

2 1 4 5

Above row ( 2nd row ) means , Node 2 is connected to Node 1 , Node 4 and Node 5

I want to read this data as a Graph. And then needs to print the Graph.
I am expecting the output as this 

1,2   
1,3   
2,1   
2,4   
2,5    
3,1   
4,2    
5,2     // not getting in output

But I am not getting Node 5 in output. I tried some other data but still last node I can not see in output.
It will be great, if anyone helped me.

Upvotes: 0

Views: 790

Answers (3)

Eklavya
Eklavya

Reputation: 18480

 vector<int>adj[N+1]; //change this line also
 for( int i = 1 ; i <= 5; i++ )   // Printing graph

Change this line .

Upvotes: 2

vianney
vianney

Reputation: 161

R Sahu has the right answer, you have an off-by-one error.

I would add that you should use c++ features to avoid this kind of errors. Hence replacing your vector<int> adj[N]; with vector<vector<int>> adj; or array<vector<int>>.

Then you can use at to access your data (by ref) and catch a nice runtime error to detect your defect.

Upvotes: 1

R Sahu
R Sahu

Reputation: 206667

The line

adj[u].push_back(v);

accesses memory using an out of bounds index when u is 5. That is cause for undefined behavior. It needs to be:

adj[u-1].push_back(v);

There is also a parsing error with your code when there are whitespace characters after the numbers in a line. You can avoid the pitfalls of parsing a line using strtok by using std::istringstream. Here's my suggestion:

#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
#include <cstdlib>

using namespace std;

int main()
{
   const int N = 5;
   vector<int> adj[N];

   std::ifstream infile("socc.in");
   std::string line;

   int i = 0;
   while ( i < N && getline(infile, line) )
   {
      std::istringstream str(line);
      int u;

      str >> u;
      if ( u > N )
      {
         // Problem.
         abort();
      }

      int v;
      while ( str >> v )
      {
         adj[u-1].push_back(v);
      }
      ++i;
   }

   for( int i = 0 ; i < N; i++ )   // Printing graph
   {
      for( size_t p = 0 ; p < adj[i].size(); p++ )
      {
         cout<< i << " , "<< adj[i][p]<<endl;
      }
   }
}

Upvotes: 2

Related Questions