[djr4cfd]

Dear all,
I am trying to write my output files in vtr format and the following gives me a correct output file in ASCII.

#include <iostream>
#include <fstream>
#include <cmath>

// Function to calculate phi = sin(x) * cos(y)
double phi(double x, double y) {
    return sin(x) * cos(y);
}

int main() {
    int n = 10; // Size of the mesh (10x10)
    double step = 1.0 / (n - 1); // Step size
    
    std::ofstream outfile("output.vtr");
    
    // Writing the header
    outfile << "<?xml version=\"1.0\"?>\n";
    outfile << "<VTKFile type=\"RectilinearGrid\" version=\"0.1\" byte_order=\"LittleEndian\">\n";
    outfile << "<RectilinearGrid WholeExtent=\"0 " << n-1 << " 0 " << n-1 << " 0 0\">\n";
    outfile << "<Piece Extent=\"0 " << n-1 << " 0 " << n-1 << " 0 0\">\n";
    // Writing the scalar data (phi)
    outfile << "<PointData>\n";
    outfile << "<DataArray type=\"Float64\" Name=\"phi\" NumberOfComponents=\"1\" format=\"ascii\">\n";
    for (int j = 0; j < n; ++j) {
        for (int i = 0; i < n; ++i) {
            double x = i * step;
            double y = j * step;
            outfile << phi(x, y) << " ";
        }
    }
    outfile << "\n</DataArray>\n";
    outfile << "</PointData>\n";
    // Writing the coordinates
    outfile << "<Coordinates>\n";
    outfile << "<DataArray type=\"Float64\" Name=\"X_COORDINATES\" NumberOfComponents=\"1\" format=\"ascii\">\n";
    for (int i = 0; i < n; ++i) {
        outfile << i * step << " ";
    }
    outfile << "\n</DataArray>\n";
    outfile << "<DataArray type=\"Float64\" Name=\"Y_COORDINATES\" NumberOfComponents=\"1\" format=\"ascii\">\n";
    for (int j = 0; j < n; ++j) {
        outfile << j * step << " ";
    }
    outfile << "\n</DataArray>\n";  
    outfile << "<DataArray type=\"Float64\" Name=\"Z_COORDINATES\" NumberOfComponents=\"1\" format=\"ascii\">\n";
    outfile << "0.0 \n";
    outfile << "</DataArray>\n";
    outfile << "</Coordinates>\n";
    
    // Closing tags
    outfile << "</Piece>\n";
    outfile << "</RectilinearGrid>\n";
    outfile << "</VTKFile>\n";
    
    outfile.close();
    
    std::cout << "Output file generated: output.vtr\n";
    
    return 0;
}

To get output file in BINARY, I tried the following:

#include <iostream>
#include <fstream>
#include <cmath>

// Function to calculate phi = sin(x) * cos(y)
double phi(double x, double y) {
    return sin(x) * cos(y);
}

int main() {
    int n = 10; // Size of the mesh (10x10)
    double step = 1.0 / (n - 1); // Step size
    
    std::ofstream outfile("output.vtr");
    
    double A[n][n];
    double xx[n];
    double yy[n];
    
    for (int j = 0; j < n; ++j) {
        for (int i = 0; i < n; ++i) {
            double x = i * step;
            double y = j * step;
            //outfile << phi(x, y) << " ";
            A[i][j]= phi(x, y);
        }
    }
    
    for (int i = 0; i < n; ++i) {
        xx[i] =i * step;
    }
    
    for (int j = 0; j < n; ++j) {
        yy[j] =j * step;
    }
    
    // Writing the header
    outfile << "<?xml version=\"1.0\"?>\n";
    outfile << "<VTKFile type=\"RectilinearGrid\" version=\"0.1\" byte_order=\"LittleEndian\">\n";
    outfile << "<RectilinearGrid WholeExtent=\"0 " << n-1 << " 0 " << n-1 << " 0 0\">\n";
    outfile << "<Piece Extent=\"0 " << n-1 << " 0 " << n-1 << " 0 0\">\n";
    // Writing the scalar data (phi)
    outfile << "<PointData>\n";
    outfile << "<DataArray type=\"Int64\" Name=\"phi\" NumberOfComponents=\"1\" format=\"binary\">\n";
    for (int j = 0; j < n; ++j) {
        for (int i = 0; i < n; ++i) {
            outfile.write(reinterpret_cast<const char*>(&A[i][j]), sizeof(double));
        }
    }
    outfile << "\n</DataArray>\n";
    outfile << "</PointData>\n";
    // Writing the coordinates
    outfile << "<Coordinates>\n";
    outfile << "<DataArray type=\"Int64\" Name=\"X_COORDINATES\" NumberOfComponents=\"1\" format=\"binary\">\n";
    for (int i = 0; i < n; ++i) {
        outfile.write(reinterpret_cast<const char*>(&xx[i]), sizeof(double));
    }
    outfile << "\n</DataArray>\n";
    outfile << "<DataArray type=\"Int64\" Name=\"Y_COORDINATES\" NumberOfComponents=\"1\" format=\"binary\">\n";
    for (int j = 0; j < n; ++j) {
        outfile.write(reinterpret_cast<const char*>(&yy[j]), sizeof(double));
    }
    outfile << "\n</DataArray>\n";  
    outfile << "<DataArray type=\"Int64\" Name=\"Z_COORDINATES\" NumberOfComponents=\"1\" format=\"binary\">\n";
    double z =0.0;
    outfile.write(reinterpret_cast<const char*>(&z), sizeof(double));
    //outfile << "0.0 \n";
    outfile << "\n</DataArray>\n";
    outfile << "</Coordinates>\n";
    
    // Closing tags
    outfile << "</Piece>\n";
    outfile << "</RectilinearGrid>\n";
    outfile << "</VTKFile>\n";
    
    outfile.close();
    
    std::cout << "Output file generated: output.vtr\n";
    
    return 0;
}

The generated output is not correctly read by Paraview. It gives me the following error.

ERROR: In /builds/gitlab-kitware-sciviz-ci/build/superbuild/paraview/src/VTK/IO/XMLParser/vtkXMLParser.cxx, line 379
vtkXMLDataParser (0x1659c570): Error parsing XML in stream at line 7, column 0, byte index 255: not well-formed (invalid token)

ERROR: In /builds/gitlab-kitware-sciviz-ci/build/superbuild/paraview/src/VTK/IO/XML/vtkXMLReader.cxx, line 521
vtkXMLRectilinearGridReader (0x17dda5a0): Error parsing input file. ReadXMLInformation aborting.

I am using a Ubuntu system; byte_order is LittleEndian and using g++ compiler. Paraview version is 5.10.1.

Can anyone help me fix this. A similar example for writing binary vtr files using c++ will also help.