How do i copy files to the wii's nand using c++? (homebrew)

Question

I tried doing it this way, didn't work (no file was copied, there was no error message)

#include <stdio.h>
#include <stdlib.h>
#include <gccore.h>
#include <grrlib.h>
#include <stdio.h>
#include <fstream>
#include <wiiuse/wpad.h>
int main() {
(...)
std::ifstream src_f("nand:/title/00010004/524d4345/data/rksys.dat", std::ios::binary);
std::ofstream  dst_f("nand:/title/00010004/4a4e4b5/data/rksys.dat",std::ios::binary);
dst_f << src_f.rdbuf();
(...)
}

Do I need to initialize the NAND or something? The code worked fine when I tried to copy files to the SD card.