array

[rudra]

dear all, being a starter with C++, i am getting a problem with array.
i have a (say),NxN array in a file, from which i have to read the nXn
(n<N, obviously) chunk, and with each iteration, the size will
increase. the first problem of dynamic allocation is solved. but i am
getting a trouble that the code is reading first nxn element along row
and not the chunk. suppose i have a array:
1 2 3 4 5 6
2 3 4 5 6 7
3 4 5 6 7 8
4 5 6 7 8 9
5 6 7 8 9 0
and if i write the code
int main() {

ifstream infile ;
infile.open("file", ios::in);

const unsigned row = 4 ; // number of rows of the matrix, does not
match the row of file
const unsigned column = 3 ; // number of columns of the matrix;does
not match the column of file
// float matrix[row][column] ;

int Matrix[row][column-1] ;

for(int ii = 0; ii < row; ++ii) {
for(int jj = 0; jj < column; ++jj) {
infile >> Matrix[ii][jj] ;
cout << Matrix[ii][jj] << " " ;
}
cout << "\n" ;
}

return 0 ;

}
then we get the output:
1 2 3
4 5 6
2 3 4
5 6 7
where i am intending it should give
1 2 3
2 3 4
3 4 5
4 5 6

will you people plz help me?

 

[Eric Pruneau]

dear all, being a starter with C++, i am getting a problem with array.
i have a (say),NxN array in a file, from which i have to read the nXn
(n<N, obviously) chunk, and with each iteration, the size will
increase. the first problem of dynamic allocation is solved. but i am
getting a trouble that the code is reading first nxn element along row
and not the chunk. suppose i have a array:

Your program are not doing any dynamic allocation.

int StackArray[5]; // an array of 5 elements stored on the stack
int* HeapArray = new int[5]; // an array of 5 elements stored on the
heap

Here, HeapArray is dynamically allocated, but StackArray is not.

1 2 3 4 5 6
2 3 4 5 6 7
3 4 5 6 7 8
4 5 6 7 8 9
5 6 7 8 9 0
and if i write the code
int main() {

ifstream infile ;
infile.open("file", ios::in);

const unsigned row = 4 ; // number of rows of the matrix, does not
match the row of file
const unsigned column = 3 ; // number of columns of the matrix;does
not match the column of file
// float matrix[row][column] ;

int Matrix[row][column-1] ;

for(int ii = 0; ii < row; ++ii) {
for(int jj = 0; jj < column; ++jj) {
infile >> Matrix[ii][jj] ;
cout << Matrix[ii][jj] << " " ;
}
cout << "\n" ;
}

return 0 ;

}
then we get the output:
1 2 3
4 5 6
2 3 4
5 6 7
where i am intending it should give
1 2 3
2 3 4
3 4 5
4 5 6

will you people plz help me?

Here is a very simple solution (you should add at least some error checking)
it wont work if one of the line (in the file) has more than 256 characters.

#include <vector>
#include <sstream>

using namespace std;

int main()
{
const unsigned row = 4 ;
const unsigned column = 3;
ifstream infile("file.txt");
typedef vector<int> VecInt;
VecInt rowvec(column);
vector<VecInt> Matrix(row,rowvec);

// I assume each line in your file contain less
// than 256 characters, if not, the easiest thing
// to do is to set MaxCol to the number of char
// of your longest line
const unsigned MaxCol = 256;
char buffer[MaxCol];

for(unsigned ir = 0; ir < row; ++ir)
{
// getline will read until it reach MaxCol characters
// or until it reach a newline character
infile.getline(buffer, MaxCol);
// now extract data using istringstream
istringstream iss(buffer);
for(unsigned ic = 0; ic < column; ++ic)
iss >> Matrix[ir][ic];
}
return 0;
}

 

[James Kanze]

"rudra" <[email protected]> a écrit dans le message de (e-mail address removed)...

[...]

Here is a very simple solution (you should add at least some
error checking) it wont work if one of the line (in the file)
has more than 256 characters.

Which is easily fixed by using std::string instead of char[256].