Android, generate wav file with NDK C++

WaveFileGenerator.cpp

#include <fstream>

namespace little_endian_io
{
    template <typename Word>
    std::ostream& write_word( std::ostream& outs, Word value, unsigned size = sizeof( Word ) )
    {
        for (; size; --size, value >>= 8)
            outs.put( static_cast <char> (value & 0xFF) );
        return outs;
    }
}
using namespace little_endian_io;


// <BEGIN> Wav file generator (Works also with Android NDK C++) ; Initial work : https://www.cplusplus.com/forum/beginner/166954/
        std::ofstream f;
        const char *path = "/storage/emulated/0/Music/record.wav";
        f.open(path, std::ios::binary);
        // Write the file headers
        f << "RIFF----WAVEfmt ";     // (chunk size to be filled in later)
        write_word( f,     16, 4 );  // no extension data
        write_word( f,      1, 2 );  // PCM - integer samples
        write_word( f,      2, 2 );  // two channels (stereo file)
        write_word( f,  44100, 4 );  // samples per second (Hz)
        write_word( f, 176400, 4 );  // (Sample Rate * BitsPerSample * Channels) / 8
        write_word( f,      4, 2 );  // data block size (size of two integer samples, one for each channel, in bytes)
        write_word( f,     16, 2 );  // number of bits per sample (use a multiple of 8)
        // Write the data chunk header
        size_t data_chunk_pos = f.tellp();
        f << "data----";  // (chunk size to be filled in later)        f.flush();
        // Write the audio samples
        // (We'll generate a single C4 note with a sine wave, fading from left to right)
        constexpr double two_pi = 6.283185307179586476925286766559;
        constexpr double max_amplitude = 32760;  // "volume"

        double hz        = 44100;    // samples per second
        double frequency = 528;//261.626;  // middle C
        double seconds   = 10;      // time

        int N = hz * seconds;  // total number of samples
        for (int n = 0; n < N; n++)
        {
            double amplitude = (double)n / N * max_amplitude;
            double value     = sin( (two_pi * n * frequency) / hz );
            write_word( f, (int)(                 amplitude  * value), 2 );
            write_word( f, (int)((max_amplitude - amplitude) * value), 2 );
        }

        // (We'll need the final file size to fix the chunk sizes above)
        size_t file_length = f.tellp();

        // Fix the data chunk header to contain the data size
        f.seekp( data_chunk_pos + 4 );
        write_word( f, file_length - data_chunk_pos + 8 );

        // Fix the file header to contain the proper RIFF chunk size, which is (file size - 8) bytes
        f.seekp( 0 + 4 );
        write_word( f, file_length - 8, 4 );
        f.close();
        // <END> Wav file generator