Handling binary data in C - questions

[Bruce Lee]

Hi
I have the following 2 questions:
1.How to write binary data to a text file in C? I have a number like
10001010110001 say, I need to put it in the text file so that I can see
the corresponding characters when I open the file.

2. How to extract bits from a byte. I think it is using bit operations,
but for example, how would I extract the 2nd most significant bit in a
byte?

Thanks
Bruce

[Neil Kurzman]

Bruce Lee wrote:

Hi
I have the following 2 questions:
1.How to write binary data to a text file in C? I have a number like
10001010110001 say, I need to put it in the text file so that I can see
the corresponding characters when I open the file.

2. How to extract bits from a byte. I think it is using bit operations,
but for example, how would I extract the 2nd most significant bit in a
byte?

Thanks
Bruce

1. mask a bit print a 0 or 1 , shift left and repeat.

2. Mask using and (&)

ex :
if(abyte & 0x04)printf("1" ); // mask bit 2 0x04 = 00000100
else printf("0");

[Bruce Lee]

Sorry but I am still new to C and unable to understand you clearly

1. How to print it? fprintf(fileNum ,"%s","write this"); is what I know.
And I guess %s can be %c as well.
But how to print a bit as you said (0 or 1)? What is the command to
print just 0s and 1s to a file?

2. This masks the 3rd bit from the right since 0x04 is 100? Does &-ing
give a boolean result or an int? In this case, what does abyte & 00x4
return?

Thanks for the explanation
Bruce

[Stan Milam]

Bruce Lee wrote:

Sorry but I am still new to C and unable to understand you clearly

1. How to print it? fprintf(fileNum ,"%s","write this"); is what I know.
And I guess %s can be %c as well.
But how to print a bit as you said (0 or 1)? What is the command to
print just 0s and 1s to a file?

2. This masks the 3rd bit from the right since 0x04 is 100? Does &-ing
give a boolean result or an int? In this case, what does abyte & 00x4
return?

Thanks for the explanation
Bruce

try this:

fprintf(stdout, "%c", data & 0x4 ? '1' : '0');

This will print out a '1' if the 3rd bit is on and '0' if not. It will
be printed to your terminal. If you want the result to go to a
different file just substitue your file pointer in place of stdout.
--
Regards,
Stan Milam
=============== =============== =============== =============== =
Charter Member of The Society for Mediocre Guitar Playing on
Expensive Instruments, Ltd.
=============== =============== =============== =============== =

[Bruce Lee]

Stan Milam wrote:

Bruce Lee wrote:

Sorry but I am still new to C and unable to understand you clearly

1. How to print it? fprintf(fileNum ,"%s","write this"); is what I know. And I guess %s can be %c as well.
But how to print a bit as you said (0 or 1)? What is the command to
print just 0s and 1s to a file?

2. This masks the 3rd bit from the right since 0x04 is 100? Does &-ing give a boolean result or an int? In this case, what does abyte & 00x4 return?

Thanks for the explanation
Bruce

try this:

fprintf(stdout, "%c", data & 0x4 ? '1' : '0');

This will print out a '1' if the 3rd bit is on and '0' if not. It

will be printed to your terminal. If you want the result to go to a
different file just substitue your file pointer in place of stdout.
--
Regards,
Stan Milam
=============== =============== =============== =============== =
Charter Member of The Society for Mediocre Guitar Playing on
Expensive Instruments, Ltd.
=============== =============== =============== =============== =

Thanks, but data & 0x4 need not necessarily give a 0 or 1 right? I
mean, if data is 11011000 & 0x4, the result would be 0010000
How do I write the bits to a file using fprintf (or anything else)?
If my character is a, its ascii value will be in bits 1100001. I have
this and I need to write it to the file so that the file has the char
'a'.
Could someone please explain this bit extraction and writing?
Thanks
Bruce

[GrandElf]

maybe you don't need bit operations.plea se look at the simple code
fragment:
void main()
{
FILE *fp;
fp = fopen("d:\\a.tx t","w+");
printf("---------------\n");
if(fp==NULL)
{
printf("fail to open file \n");
return;
}
fprintf(fp,"%c" ,'a');
fclose(fp);

return;
}
the program is complied in TC20,it only do create a file "a.txt" on
d:\.The content of a.txt
is 'a'.

[infobahn]

GrandElf wrote:

maybe you don't need bit operations.plea se look at the simple code
fragment:
1
void main()
2, 3
{
FILE *fp;
4
fp = fopen("d:\\a.tx t","w+");
5
printf("---------------\n");
if(fp==NULL)
{
printf("fail to open file \n");
6
return;
7
}
fprintf(fp,"%c" ,'a');
8
fclose(fp);

return;
9
}

A: Do some research, to find out why your code is broken (the numbers
should give you a few hints as to where the problems are).

B: Fix those problems.

C: Try re-posting if you wish. Of course, the OP might have got bored
of waiting by then.

[Richard Bos]

"GrandElf" <Ni*******@gmai l.com> wrote:

maybe you don't need bit operations.plea se look at the simple code
fragment:
void main()
{
FILE *fp;
fp = fopen("d:\\a.tx t","w+");
printf("---------------\n");
if(fp==NULL)
{
printf("fail to open file \n");
return;
}
fprintf(fp,"%c" ,'a');
fclose(fp);

return;
}

And how does this non-conforming, badly indented (learn to use Google
Broken Beta correctly or get a real newsreader!) code, with a
system-specific filename, help even the slightest bit with the OP's
problem, which is outputting the binary representation of an object?
Even if we assume a single interpretation of "binary representation"
(there are two reasonable ones), your code does not reliably output
either of those for all objects.

Richard

[Keith Thompson]

rl*@hoekstra-uitgeverij.nl (Richard Bos) writes:
[...]

badly indented (learn to use Google Broken Beta correctly or get a
real newsreader!) code

[...]

Unfortunately, it's not possible to indent code correctly using Google
Broken Beta. You can work around it by prefixing each line with a '.'
character, or use groups.google.c a (which, last time I checked, still
uses the old interface), or, as you suggest, get a real newsreader.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.