Faster I/O in C

Question

I have a problem which will take 1000000 lines of inputs like below from console.

0 1 23 4 5
1 3 5 2 56
12 2 3 33 5
...
...

I have used scanf,

Answer 1

fread will still return if you try to read more bytes than there are.

I have found on of the fastest ways to read file is like this:

/*seek end of file */ fseek(file,0,SEEK_END);

/*get size of file */ size = ftell(file);

/*seek start of file */ fseek(file,0,SEEK_SET);

/* make a buffer for the file */ buffer = malloc(1048576);

/*fread in 1MB at a time until you reach size bytes etc */

On modern computers put your ram to use and load the whole thing to ram, then you can easily work your way through the memory.

At the very least you should be using fread with block sizes as big as you can, and at least as big as the cache blocks or HDD sector size (4096 bytes minimum, I would use 1048576 as a minimum personally). You will find that with much bigger read requsts rfead is able to sequentially get a big stream in one operation. The suggestion here of some people to use 128 bytes is rediculous.... as you will end up with the drive having to seek all the time as the tiny delay between calls will cause the head to already be past the next sector which almost certainly has sequential data that you want.