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creating dynamic array

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tonyaim83

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creating dynamic array

Aug 24th, 2007

I m reading a text file which is of format
L1,L2,L3
L1,0,0,0
L2,1,0,0
L3,1,0,0

using getline method. The first lines signifies the vertex of a graph. Now from the second line onwards it signifies edges.
Now from second line onwards i want to add the elements in a dynamic array through vector so that i can create edges.
Kindly suggest the method for that..

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Re: creating dynamic array

Aug 24th, 2007

vector does all the dynmaic allocation for you -- just call its push_back() method to add a new row.

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string line;
vector<string> array;
...
// now put this inside the file read loop just after getline()
array.push_back(line);
string line;
vector<string> array;
...
// now put this inside the file read loop just after getline()
array.push_back(line);

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

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Re: creating dynamic array

Aug 27th, 2007

That's true but i have to also make sure that if the value is 1 then i have to create edges between the given vertex.

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Re: creating dynamic array

Aug 27th, 2007

Maybe a linked list of some sort may be a better idea?

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Re: creating dynamic array

Aug 27th, 2007

How do i create a 2-D array using a vector which is dynamic in nature. Also let me know if how we can make use of "find" in this case.

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Re: creating dynamic array

Aug 27th, 2007

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Originally Posted by tonyaim83

How do i create a 2-D array using a vector which is dynamic in nature.

You can make use of vector<vector<T> >

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Re: creating dynamic array

Aug 27th, 2007

you can repesent a graph as an adjacency matrix. http://www.cs.usask.ca/resources/tut...es/matrix.html
using the specialization vector<bool> would take only one bit per matrix element, so large graphs can be accommodated. (not withstanding my efforts, the daniweb formatter refuses to believe that this sentence is not a url)

 Help with Code Tags 
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#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <boost/algorithm/string.hpp>
#include <cassert>
using namespace std ;
using namespace boost ;
 
typedef vector< vector<bool> > adjacency_matrix ;
 
int main()
{
  vector<string> vertices ;
  ifstream file( "whatever.txt" ) ;
  string line ;
 
  // read and parse the first line
  assert( getline( cin, line ) ) ;
  split( vertices, line, is_any_of(", ") );
 
  const size_t N = vertices.size() ;
  adjacency_matrix graph( N, vector<bool>(N) ) ;
 
  // read and parse subsequent lines
  size_t i = 0 ;
  while( getline( cin, line ) )
  {
    vector<string> elements ;
    split( elements, line, is_any_of(", ") );
    assert( (i<N) && (vertices[i]==elements[0]) && (elements.size()==N+1) ) ;
    ++i ;
    for( size_t j=0 ; j<N ; ++j )
      graph[i][j] = elements[j+1] == "1" ;
  }
  assert( i == N ) ;
}
#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <boost/algorithm/string.hpp>
#include <cassert>
using namespace std ;
using namespace boost ;

typedef vector< vector<bool> > adjacency_matrix ;

int main()
{
  vector<string> vertices ;
  ifstream file( "whatever.txt" ) ;
  string line ;
  
  // read and parse the first line
  assert( getline( cin, line ) ) ;
  split( vertices, line, is_any_of(", ") );

  const size_t N = vertices.size() ;
  adjacency_matrix graph( N, vector<bool>(N) ) ;

  // read and parse subsequent lines
  size_t i = 0 ;
  while( getline( cin, line ) )
  {
    vector<string> elements ;
    split( elements, line, is_any_of(", ") );
    assert( (i<N) && (vertices[i]==elements[0]) && (elements.size()==N+1) ) ;
    ++i ;
    for( size_t j=0 ; j<N ; ++j )
      graph[i][j] = elements[j+1] == "1" ;
  }
  assert( i == N ) ;
}

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Re: creating dynamic array

Aug 27th, 2007

can u expain what this code signifies

split( elements, line, is_any_of(", ") );
assert( (i<N) && (vertices[i]==elements[0]) && (elements.size()==N+1) ) ; ++i ;
for( size_t j=0 ; j<N ; ++j )
graph[i][j] = elements[j+1] == "1" ;

Also how do i print the edge values..

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Re: creating dynamic array

Aug 27th, 2007

Also your code given code gives following compilation errors:-

:\srlgrp\boostlib\boost_1_34_0\boost\algorithm\string\yes_no_type.hpp(22) : error C2265: '<Unknown>' : reference to a zero-sized array is illegal
c:\srlgrp\boostlib\boost_1_34_0\boost\algorithm\string\yes_no_type.hpp(23) : see reference to class template instantiation 'boost::algorithm::size_descriptor<I>' being compiled
c:\srlgrp\boostlib\boost_1_34_0\boost\mpl\bool.hpp(37) : fatal error C1506: unrecoverable block scoping error

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Re: creating dynamic array

#10

Aug 27th, 2007

>> can u expain what this code signifies
>> split( elements, line, is_any_of(", ") );
split() is used to split string line into parts separated by characters ',' or space. these parts are then put into the vector elements
>> assert( (i<N) && (vertices[i]==elements[0]) && (elements.size()==N+1) ) ;
verify that the input is sane
>> for( size_t j=0 ; j<N ; ++j )
graph[i][j] = elements[j+1] == "1" ;
if the element in the string part is "1", set the corrosponding element in the adjacency matrix to true.
>> Also your code given code gives following compilation errors
it does not for me; i'm using boost_1_34_1 (not boost_1_34_0), but i'm certain that boost_1_34_0 should be ok.

there were two errors in the earlier code; ++i (line 32) should me moved to the end of the while loop. also, getline( cin, line ) should be changed to getline( file, line ).
here is the modified code with a testcase and some diagnostic output.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <boost/algorithm/string.hpp>
#include <cassert>
#include <algorithm>
#include <iterator>
using namespace std ;
using namespace boost ;
 
typedef vector< vector<bool> > adjacency_matrix ;
 
int main()
{
  vector<string> vertices ;
  ifstream file( "graph.txt" ) ;
  string line ;
 
  // read and parse the first line
  assert( getline( file, line ) ) ;
  split( vertices, line, is_any_of(", ") );
 
  const size_t N = vertices.size() ;
  adjacency_matrix graph( N, vector<bool>(N) ) ;
 
  // read and parse subsequent lines
  size_t i = 0 ;
  while( getline( file, line ) )
  {
    vector<string> elements ;
    split( elements, line, is_any_of(", ") );
    assert( ( i<N ) && ( vertices[i]==elements[0] ) 
                      && (elements.size()==N+1) ) ;
    for( size_t j=0 ; j<N ; ++j )
      graph[i][j] = elements[j+1] == "1" ;
    cout << line << " => " ;
    copy( graph[i].begin(), graph[i].end(), 
               ostream_iterator<int>(cout," ") ) ;
    cout << '\n' ;
    ++i ;
  }
  assert( i == N ) ;
}
 
/** graph.txt
L1,L2,L3,L4,L5
L1,0,0,0,1,0
L2,1,0,0,0,1
L3,1,0,0,0,0
L4,0,1,1,0,1
L5,0,0,1,1,0
*/
/** output
>g++ -Wall -std=c++98 -I/usr/local/include adj_matrix.cpp && ./a.out
L1,0,0,0,1,0 => 0 0 0 1 0
L2,1,0,0,0,1 => 1 0 0 0 1
L3,1,0,0,0,0 => 1 0 0 0 0
L4,0,1,1,0,1 => 0 1 1 0 1
L5,0,0,1,1,0 => 0 0 1 1 0
*/
#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <boost/algorithm/string.hpp>
#include <cassert>
#include <algorithm>
#include <iterator>
using namespace std ;
using namespace boost ;

typedef vector< vector<bool> > adjacency_matrix ;

int main()
{
  vector<string> vertices ;
  ifstream file( "graph.txt" ) ;
  string line ;

  // read and parse the first line
  assert( getline( file, line ) ) ;
  split( vertices, line, is_any_of(", ") );

  const size_t N = vertices.size() ;
  adjacency_matrix graph( N, vector<bool>(N) ) ;

  // read and parse subsequent lines
  size_t i = 0 ;
  while( getline( file, line ) )
  {
    vector<string> elements ;
    split( elements, line, is_any_of(", ") );
    assert( ( i<N ) && ( vertices[i]==elements[0] ) 
                      && (elements.size()==N+1) ) ;
    for( size_t j=0 ; j<N ; ++j )
      graph[i][j] = elements[j+1] == "1" ;
    cout << line << " => " ;
    copy( graph[i].begin(), graph[i].end(), 
               ostream_iterator<int>(cout," ") ) ;
    cout << '\n' ;
    ++i ;
  }
  assert( i == N ) ;
}

/** graph.txt
L1,L2,L3,L4,L5
L1,0,0,0,1,0
L2,1,0,0,0,1
L3,1,0,0,0,0
L4,0,1,1,0,1
L5,0,0,1,1,0
*/
/** output
>g++ -Wall -std=c++98 -I/usr/local/include adj_matrix.cpp && ./a.out
L1,0,0,0,1,0 => 0 0 0 1 0
L2,1,0,0,0,1 => 1 0 0 0 1
L3,1,0,0,0,0 => 1 0 0 0 0
L4,0,1,1,0,1 => 0 1 1 0 1
L5,0,0,1,1,0 => 0 0 1 1 0
*/