Most efficient way to copy a file in Linux

Question

I am working at an OS independent file manager, and I am looking at the most efficient way to copy a file for Linux. Windows has a built in function, CopyFileEx(), but from

Answer 1

My answer from a more recent duplicate of this post.

boost now offers mapped_file_source which portably models a memory-mapped file.

Maybe not as efficient as CopyFileEx() and splice(), but portable and succinct.

This program takes 2 filename arguments. It copies the first half of the source file to the destination file.

#include 
#include 
#include 
#include 

namespace iostreams = boost::iostreams;
int main(int argc, char** argv)
{
    if (argc != 3)
    {
        std::cerr << "usage: " << argv[0] << "   - copies half of the infile to outfile" << std::endl;
        std::exit(100);
    }

    auto source = iostreams::mapped_file_source(argv[1]);
    auto dest = std::ofstream(argv[2], std::ios::binary);
    dest.exceptions(std::ios::failbit | std::ios::badbit);
    auto first = source. begin();
    auto bytes = source.size() / 2;
    dest.write(first, bytes);
}

Depending on OS, your mileage may vary with system calls such as splice and sendfile, however note the comments in the man page:

Applications may wish to fall back to read(2)/write(2) in the case where sendfile() fails with EINVAL or ENOSYS.