Writing arrays to text files in c++

Question

I have to write some 5 to 6 large arrays of the same size to text files in C++. I am using only one "for loop" for writing all the arrays to text files. The following is the code i'm using.

ofstream kx_ecl("COARSE_PERMX.GRDECL");
ofstream ky_ecl("COARSE_PERMY.GRDECL");
ofstream kz_ecl("COARSE_PERMZ.GRDECL");
ofstream ntg_c("COARSE_NTG.GRDECL");
ofstream phi_c("COARSE_PORO.GRDECL");
ofstream multbv("MULTBRV.GRDECL");


kx_ecl<<"PERMX"<<endl;
ky_ecl<<"PERMY"<<endl;
kz_ecl<<"PERMZ"<<endl;
ntg_c<<"NTG"<<endl;
phi_c<<"PORO"<<endl;
multbv<<"MULTBRV"<<endl;

for (i=0;i<N;i++) {
    kx_ecl<<new_KX[i]<<endl;
    ky_ecl<<new_KY[i]<<endl;
    kz_ecl<<new_KZ[i]<<endl;
    ntg_c<<new_NTG[i]<<endl;
    phi_c<<new_por[i]<<endl;
    multbv<<MULTBRV[i]<<endl;
}

kx_ecl<<"/";
ky_ecl<<"/";
kz_ecl<<"/";
ntg_c<<"/";
phi_c<<"/";
multbv<<"/";
kx_ecl.close();
ky_ecl.close();
kz_ecl.close();
ntg_c.close();
phi_c.close();
multbv.close();

My question here is that is it faster if I output each of them individually one by one in which case it would have many for loops or leave it as it is. Also, is there any way to write the arrays to a file without using a for loop? I am asking because the output to files is taking a lot of time compared to the actual calculation in my code.

Answer 1

Are you aware that std::endl is flushing your ofstreams constantly? You could push out '\n' characters instead and just flush once at the end for each stream.

I/O might still end up being the biggest piece of your time spent, but you are working against the buffering and do not seem in this example at least to be gaining anything from it. Going one array/file at a time might give you infinitesimally faster performance due to better memory locality (unless you're using so much memory you're swapping pages to disk), but the difference is probably getting completely lost in the huge cost of file writing.