Reading .bmp file in C

[biplab]

Hi all,
I want to read the pixel values of a .bmp image(which will be input to
the code) into a matrix...plz help me out as i can not understand how
to achieve this...

thanks in advance

biplab

[Peter Nilsson]

Ron Ford <r...@example.i nvalidwrote:

biplab posted:

I want to read the pixel values of a .bmp image(which
will be input to the code) into a matrix...plz help me
out as i can not understand how to achieve this...

Standard C is the wrong tool for this.

Why do you say that?

--
Peter

[Ron Ford]

On Wed, 10 Sep 2008 19:44:06 -0700 (PDT), Peter Nilsson posted:

Ron Ford <r...@example.i nvalidwrote:

>biplab posted:

>>I want to read the pixel values of a .bmp image(which
will be input to the code) into a matrix...plz help me
out as i can not understand how to achieve this...

Standard C is the wrong tool for this.

Why do you say that?

Because extensions make this easy.
--
War will never cease until babies begin to come into the world with larger
cerebrums and smaller adrenal glands. 2
H. L. Mencken

[Malcolm McLean]

"Ron Ford" <ro*@example.in validwrote in message

>
Because extensions make this easy.

You're right. For instance BMP files can be jpeg-compressed. This happens
but rarely, but it is in the file format. You are much better off calling an
image-loading routine supplied by Microsoft.
Unless that is you are not on a Windows machine.

--
Free games and programming goodies.
http://www.personal.leeds.ac.uk/~bgy1mm

[Bill Cunningham]

"Malcolm McLean" <re*******@btin ternet.comwrote in message
news:5q******** *************** *******@bt.com. ..

However if we say

int width;

width = fgetc(fp);
width |= fgetc(fp) << 8;

Then we retrieve the right value of width, regardless of whether integers
are 2 bytes or 4 bytes, or big- or little- endian.

Ok I have no real experience with the binary operators so I'm going to
say your pipe symbol | is XOR. << is the left shift operator for an 8 bit
value. I really don't know yet how to use this in real time but I recognize
the symbols.

Bill

[vippstar]

On Sep 11, 11:46 pm, "Bill Cunningham" <nos...@nspam.c omwrote:

"Malcolm McLean" <regniz...@btin ternet.comwrote in message

news:5q******** *************** *******@bt.com. ..

However if we say

int width;

width = fgetc(fp);
width |= fgetc(fp) << 8;

Then we retrieve the right value of width, regardless of whether integers
are 2 bytes or 4 bytes, or big- or little- endian.

Ok I have no real experience with the binary operators so I'm going to
say your pipe symbol | is XOR.

lol.

[Richard Heathfield]

Bill Cunningham said:

<snip>

Ok I have no real experience with the binary operators so I'm going
to
say your pipe symbol | is XOR.

That's the wrong way to learn. Instead of guessing, consult your C
reference, which makes the roles of bitwise operators perfectly clear.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Keith Thompson]

vi******@gmail. com writes:

On Sep 10, 9:47 pm, [e-mail] m wrote:

>On Sep 10, 8:21 am, biplab <getbip...@gmai l.comwrote:

<snip>

1st of all i will be highly obliged if you let me know what the code
is doing and how??/As i have found the code in the internet and am a
newbie in C...
thanks in advance...

The code doesn't do much. It invokes undefined behavior

- at line 1 in main() (calling gets() with an uninitialized pointer)

Well, not really.

Well, yes, really.

That code would fail to translate, because of the non-standard
headers.

It *might* fail to translate, depending on the implementation. Unless
there's a statement in the standard that I've missed that says
anything that includes a non-standard header must fail to translate.
(Hint: There isn't.)

If not, how can you guess the contents of the non-standard
headers?
For example, <dos.hmight had:

#undef gets
#define gets(x) (void)0

You can't *know* the contents of non-standard headers, but you can
certainly *guess*. For example, I guess, with a fairly high level of
confidence, that a <dos.hheader in any implementation that provides
it *doesn't* have the above macro definition.

The fact that <dos.his non-standard, and therefore off-topic in this
newsgroup, doesn't mean that we can or should pretend that it doesn't
exist or that it's likely to contain some implausible content.
Writing non-portable code is one of the main purposes of C, after all.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Keith Thompson]

"Bill Cunningham" <no****@nspam.c omwrites:

"Malcolm McLean" <re*******@btin ternet.comwrote in message
news:5q******** *************** *******@bt.com. ..

>However if we say

int width;

width = fgetc(fp);
width |= fgetc(fp) << 8;

Then we retrieve the right value of width, regardless of whether integers
are 2 bytes or 4 bytes, or big- or little- endian.

Ok I have no real experience with the binary operators so I'm going to
say your pipe symbol | is XOR. << is the left shift operator for an 8 bit
value. I really don't know yet how to use this in real time but I recognize
the symbols.

They're better referred to as bitwise operators. The term "binary
operator" commonly refers to an operator that takes two operands.

Your lack of experience with bitwise operators is no excuse for
*guessing* what they mean. "|" is not XOR. Consult your copy of
K&R2 (you've said you have one) to learn what it is, and what the
actual XOR operator looks like.

(Yes, << is the left shift operator, but it's not specific to 8
bit values.)

Last month, I gave you some advice about
the use of standard library functions. See
<http://groups.google.c om/group/comp.lang.c/msg/6da991ad26d30ed 9>.
Everything I wrote there applies equally to predefined operators,
at least to any that you're not familiar with. (At least this
time you're not writing code based on your guesses.)

One more thing: you're using <no****@nspam.c omas your return
address, obviously to avoid spam. nspam.com happens to be a
real domain. I'm sure its owner doesn't appreciate getting
all the spam that would have gone to you. Use something like
<no****@nospam. invalid(see RFC 2606).

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[vippstar]

On Sep 12, 12:29 am, Keith Thompson <[e-mail] rote:

vipps...@gmail. com writes:

On Sep 10, 9:47 pm, [e-mail] m wrote:

The code doesn't do much. It invokes undefined behavior
- at line 1 in main() (calling gets() with an uninitialized pointer)

Well, not really.

Well, yes, really.

That code would fail to translate, because of the non-standard
headers.

It *might* fail to translate, depending on the implementation. Unless

Reading further,
"if not [...]"
So I did not say that it _must_ fail. I examined each posibility.
(I accept that this may not have been obvious, but these were my
intentions)

there's a statement in the standard that I've missed that says
anything that includes a non-standard header must fail to translate.
(Hint: There isn't.)

If not, how can you guess the contents of the non-standard
headers?
For example, <dos.hmight had:

#undef gets
#define gets(x) (void)0

You can't *know* the contents of non-standard headers, but you can
certainly *guess*. For example, I guess, with a fairly high level of
confidence, that a <dos.hheader in any implementation that provides
it *doesn't* have the above macro definition.

The fact that <dos.his non-standard, and therefore off-topic in this
newsgroup, doesn't mean that we can or should pretend that it doesn't
exist or that it's likely to contain some implausible content.
Writing non-portable code is one of the main purposes of C, after all.

I disagree. After all, nasal demons were given life here. :-)
(according to the jargon file, comp.std.c actually)
Being more serious here, of course that gets call invoked undefined
behavior. However, don't you agree my post had some truth hidden in
it? You can't assume what happends if you don't know what the headers
do.

Plus, who knows, there might be an implementation whose header (one of
the non-standard headers) does have such (or similar) macro
definition, to prevent people from using gets.

[Richard]

"Bill Cunningham" <no****@nspam.c omwrites:

"Malcolm McLean" <re*******@btin ternet.comwrote in message
news:5q******** *************** *******@bt.com. ..

>However if we say

int width;

width = fgetc(fp);
width |= fgetc(fp) << 8;

Then we retrieve the right value of width, regardless of whether integers
are 2 bytes or 4 bytes, or big- or little- endian.

Ok I have no real experience with the binary operators so I'm going to
say your pipe symbol | is XOR. << is the left shift operator for an 8 bit
value. I really don't know yet how to use this in real time but I recognize
the symbols.

Bill

Wonderful Bill! You're trolling knows no bounds!

Pipe symbol is XOR. Priceless.