How to read/write sets of orderded numbers in binary

[kaydknight]

Hello, I would like to ask a question.

Does anyone know how to effectively store a 2d array of numbers in binary file, and then able to read them later into array.

For example, This are the samples of numbers I need to write:

x1 x2 x3
y1 1 1 1
y2 2 2 3
y3 3 3 5
y4 4 5 6
y5 5 6 8

If in ascii, I can write like this:
1 1 1
2 2 2
3 3 5
...
5 6 8

But how about writing it into binary file?
When reading, How do I know when I reached end-of-row for one column and store next number on column+1 (since binary files are ordered sequentially).
I've been thinking of putting some kind of byte signal to indicate I reached end-of-row, but I don't have the idea how.
Also, I predict a problem, where later, my sets of number will be non-uniformed (1 col have 5 rows, next col have 9 rows and so on).

Can anyone give a simple example how to write it? I'm comfortable with using QDataStream and iostreams binary mode, but I think this is more a problem of the design of it.

E.g : After reading the binary file, I want to store them into array.
array[0,0] = 1
... and so on until
array[2,4] = 8

Thanks in advance! I've tried googling, but they only tell me the basics of binary read/write.