Bits in files

Hey everyone,

I've been doing some looking at writing out in binary form to files and i think it looks like a byte is the smallest ammount

of info that can be written to a file. Is this true?

I want to store some info in a particular configuration in a file. ex.

Say i want to store the info

Gate 1, Number 3, color green
Gate 2, Number 5, color red

instead of storing the info on each line i want to store it vertically

1 2

3 5

g r
r e
e d
e
n

but i also have a key that denotes green as 1, and red as 2.

so my info looks like

1 2

3 5

1 2

but i want this to be in binary form (it makes the subsequent reading of these files easier)

1 0
0 1
0 0

1 0
1 1
0 1

1 0
0 1
0 0

(i only have the space in between bits to show what i mean).

I've looked at the write command but a character is the smallest thing it appears to write (the same as put).

Has anyone ever needed to have bits in exact positions in a file outputted by a C++ program before?

If i have a large number of arrays storing the binary of each number and writing bit 0 across each line, then bit 1, then bit

2 and so forth, is it actually writing binary 1s and 0s or the character 1, and the character 0? 1 bit is alot smaller than a

1 byte character so i'm hoping to find a way of writing the bits.

I've written some code

Code:

---


#include <iostream>
#include <fstream>
using namespace std;

int main()
{
        ofstream outFile;

        char file[9] = "out3.bin";

        int a = 0;
        int b = 1;

        outFile.open(file, ios::out | ios::binary | ios::app);

        outFile.write((char *) &a, sizeof(a));
        outFile.write((char *) &b, sizeof(b));
        outFile.write((char *) &a, sizeof(a));
        outFile.write((char *) &b, sizeof(b));
        outFile.write((char *) &a, sizeof(a));

        outFile.close();

        return 0;
}

---

Which shud place 01010 into file out3.bin, if i try and view this file it's jibberish. Shud i be able to see 01010 on screen?

Also how do i write to the next line in binary mode, do i have to use seekp - just wonderin if there's an easier way to just

say next line or something (using seek may take 2 or 3 lines of code instead of a potentially handy one).


Cheers,

Rob.

You're right. You can't read/write a single bit.

The "binary" file format doesn't really mean binary... it means anything but text. Actually, it could be text, but you'd have to format the linefeed/carrrage return manually.

And, "store it vertically" is confusing to me. All the characters & variables are going to be stored sequentially. You can read them back and display them in your preferred format.

You have to do your base-convesion during input-output... to the C++ program it's just a char, or an int (which, ironically is stored in binary-bits!) So you have to tell the program "here's a number in binary format", and "display this number in binary format".

Binary input-output is tricky in C++ (Hex and octal are easier.) One way is to use <bitset.h>. There is another method using enumerated variables... but the technique escapes me at the moment.... I think it's similar to your a=0, b=1 thechnique, where each bit is stored as a whole char or int.