Binary (hex) files and converting hex to ascii characters

[Guest_imported]

Hello
One of the things that I have to do is to read a binery file containing messages.
I have to read one bit(character) at the time, so I can compare it to my message key. If my message key is 15 then I have to search the file until I find the hex bit that is the number 15. After I have found the 15 which means that my message is starting than I have to take all the bits after that one until I find another bit say he 0x3 that menas end of message. I have to take all the bits (hex) and convert it to ascii so I can display my message. After that I still need to continue to do the same thing and check for my messages until the file end.
(what I'm trying to do is to simulate the data-link layer).

Thank you

 

[victorv]

Hi,

confusion !!

I belive that your "bit" is byte ( 8 bit ), right ?

Computer files are all binary object, memory areas too.

We call text-files, those that contains bytes in the range

from 32 decimal ( the space char in ascii rappr. )
to 126 decimal ( the tilde char, more or less ).

If a file contains for example 4 bytes:

physically in bit

01000000 01000001 01000010 00001010

I can intepreter them as:

a text file with 3 bytes of text

decimal
64 65 66 10

ascii
@ A B newline

or for me they can be 2 16-bit words

16449 16906

or 1 32 bit word (longword)

1078018570

Then, the files contain bits, when I print on paper their
value, I can choice to print the same value in:

binary ( rare )
decimal ( often )
hex ( sometime )
ascii rap ( often )

Suppose :

char c=65 ;

printf( "%d", c ) -----> 65
printf( "%c", c ) -----> A
printf( "%x", c ) -----> 41
printf( "%o", c ) -----> 101

- - - - - - - - - - -

Back to your problem.

Has your file a fixed record len ? ( the messages have all
the same lenght ? )

Your binary file containing a 0x03 means that

1) I have a bit 00000011
or
2) a text file with written inside 0x03 in text
or
3) other ?.

I first case you have to use _read function (or ReadFile)

and rc=_read( myhandle, mybuf, 1 ) // if the len is 1 byte

int len = mybuf[0] ;

rc=_read( myhandle, mybuf, len )

If the len on file is a word, you can

WORD wLen;
rc= _read( myhandle, &wLen, 2 ) ;

Be careful in binary rappr can be swapped from a processor
to another ( little or big indian )


bye .