Array I/O (Blitz++)

The current version of Blitz++ includes rudimentary output formatting for arrays. Here’s an example:

#include <blitz/array.h>

using namespace blitz;

int main()
{
    Array<int,2> A(4,5,FortranArray<2>());
    firstIndex i;
    secondIndex j;
    A = 10*i + j;

    cout << "A = " << A << endl;

    Array<float,1> B(20);
    B = exp(-i/100.);
    
    cout << "B = " << endl << B << endl;

    return 0;
}

A = (1,4) x (1,5)
[ 11 12 13 14 15 
  21 22 23 24 25 
  31 32 33 34 35 
  41 42 43 44 45 ]

B = 
(0,19)
[ 1 0.99005 0.980199 0.970446 0.960789 0.951229 0.941765 0.932394 0.923116 
0.913931 0.904837 0.895834 0.88692 0.878095 0.869358 0.860708 0.852144 0.843665 
0.83527 0.826959 ]

2.8.2 Inputting arrays

Caution: you must know the dimensionality of the array being restored from the stream. The >> operator expects an array in the same input format as generated by the << operator, namely:

Here is an example of saving and restoring arrays from files. You can find this example in the Blitz++ distribution as examples/io.cpp.

#include <blitz/array.h>
#ifdef BZ_HAVE_STD
	#include <fstream>
#else
	#include <fstream.h>
#endif

BZ_USING_NAMESPACE(blitz)

const char* filename = "io.data";

void write_arrays()
{
    ofstream ofs(filename);
    if (ofs.bad())
    {
        cerr << "Unable to write to file: " << filename << endl;
        exit(1);
    }

    Array<float,3> A(3,4,5);
    A = 111 + tensor::i + 10 * tensor::j + 100 * tensor::k;
    ofs << A << endl;

    Array<float,2> B(3,4);
    B = 11 + tensor::i + 10 * tensor::j;
    ofs << B << endl;

    Array<float,1> C(4);
    C = 1 + tensor::i;
    ofs << C << endl;
}

int main()
{
    write_arrays();

    ifstream ifs(filename);
    if (ifs.bad())
    {
        cerr << "Unable to open file: " << filename << endl;
        exit(1);
    }

    Array<float,3> A;
    Array<float,2> B;
    Array<float,1> C;

    ifs >> A >> B >> C;

    cout << "Arrays restored from file: " << A << B << C << endl;

    return 0;
}

Caution: The storage order and starting indices are not restored from the input stream. If you are restoring (for example) a Fortran-style array, you must create a Fortran-style array, and then restore it. For example, this code restores a Fortran-style array from the standard input stream:

2.8 Inputting and Outputting Arrays

2.8.1 Output formatting

2.8.2 Inputting arrays