binary files in C

sagar13 · 10-02-2004, 12:56 AM

Hi,
I want to read a binary file (say *.jpg ) in C and rewrite it to some other new file.
How can I do that ?

vharishankar · 10-02-2004, 02:15 AM

You can use the standard C stdio file stream to do this. Make sure you open the file in binary mode.

Hko · 10-02-2004, 06:31 AM

Note: Opening a file in "binary" mode or in in "text mode" does not make any difference in UNIX/Linux. It has effect only on DOS/Windows (and MacOS?)

vharishankar · 10-02-2004, 06:34 AM

Thanks for point that out

onnyloh · 10-02-2004, 09:35 AM

are u sure?

Quote:

Originally posted by Hko
Note: Opening a file in "binary" mode or in in "text mode" does not make any difference in UNIX/Linux. It has effect only on DOS/Windows (and MacOS?)

Hko · 10-02-2004, 10:01 AM

Quote:

Originally posted by onnyloh
are u sure?

As I indicated, I'm not sure about Mac-OS.
For the rest: Yes, I'm definitely sure.

mirradric · 10-02-2004, 10:04 AM

Yes. The main reason why we need to use text/binary modes is that windows/dos treats a line break as 2 characters. ( Can't rem which 2 though, never bother to remember). When a file is in text mode, the windows io calls will convert instances of the \n character into it's 2 components and vice versa. It does not do this translation if the file is in binary mode. On *nix, a line break is just a single character; so there is no need for such translation at all. There is no distinction of a text file and a binary file on a *nix. (other than the kinds of ..err.. bytes you can find in them)

Hko · 10-02-2004, 10:13 AM

It may still be a good idea to specify mode "b" with fopen(), just in case the program is going to be ported to Windows/DOS one day...

mirradric · 10-02-2004, 10:14 AM

If I didn't remember wrongy, pre-OS X macs uses the other character. I suspect OS X should follow the *nix way

itsme86 · 10-02-2004, 11:12 AM

Directly from 'man fopen':

Quote:

The mode string can also include the letter ``b'' either
as a last character or as a character between the charac-
ters in any of the two-character strings described above.
This is strictly for compatibility with ANSI X3.159-1989
(``ANSI C'') and has no effect; the ``b'' is ignored on
all POSIX conforming systems, including Linux. (Other
systems may treat text files and binary files differently,
and adding the ``b'' may be a good idea if you do I/O to a
binary file and expect that your program may be ported to
non-Unix environments.)

onnyloh · 10-02-2004, 01:29 PM

sigh, I put 'b' in fopen for a binary I/O all the ways.
Never know that this is useless...
:S