Thread: file id

i want my program to be able to figure out if an input file
is one that was generated from it.
How can i use the magic number technique ?
Are there any other portable ways ?

TIA

c++ imposes no structure on files it is entirely up to the programmer to structure his files exactly as he sees fit. So invent your own file format that will uniquely identify data files as belonging to your app.

that's exactly what i want to do.
i know the structure should be of my choice,
but i'm asking for any common or popular ways to do so.
I just want the doc for them

One of my books told me ways to make magic numbers for files, I will look at it and post it when I get home this afternoon.

Much like graphics files or other common file formats, write a file header first. The first N bytes are this, the next N bytes are that... etc. Then add your data after it. You may want to jump over to Wotsit and look at a few file formats to get an idea of how things are commonly done.

Quzah.

One method for choosing a magic number is choosing the first four letters of a program name(i.e, list) and then convert them to hexadecimal: 0x6C607374 then add 0x808080 to the number, producing the magic number of 0xECE0F3F4

this algorythm generates a magic number that is probably unique. The high bit is set on each byte to make the byte non-ANCII and avoid confusion between caps and ascii files

from Practicle C by, Steve Oualline

That is one way to go