Question

Which is faster? ifstream or fread.
Which should I use to read binary files?

fread() puts the whole file into the memory.
So after fread, accessing the buffer it creates is fast.

Does ifstream::open() puts the whole file into the memory?
or does it access the hard disk every time we run ifstream::read()?

So… does ifstream::open() == fread()?
or (ifstream::open(); ifstream::read(file_length);) == fread()?

Or shall I use ifstream::rdbuf()->read()?

edit:
My readFile() method now looks something like this:

void readFile()
{
    std::ifstream fin;
    fin.open("largefile.dat", ifstream::binary | ifstream::in);
    // in each of these small read methods, there are at least 1 fin.read()
    // call inside.
    readHeaderInfo(fin);
    readPreference(fin);
    readMainContent(fin);
    readVolumeData(fin);
    readTextureData(fin);
    fin.close();
}

Will the multiple fin.read() calls in the small methods slow down the program?
Shall I only use 1 fin.read() in the main method and pass the buffer into the small methods? I guess I am going to write a small program to test.

Thanks!

Answer 1

Are you really sure about fread putting the whole file into memory? File access can be buffered, but I doubt that you really get the whole file put into memory. I think ifstream::read just uses fread under the hood in a more C++ conformant way (and is therefore the standard way of reading binary information from a file in C++). I doubt that there is a significant performance difference.

To use fread, the file has to be open. It doesn’t take just a file and put it into memory at once. so ifstream::open == fopen and ifstream::read == fread.