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fprintf format specifiers

 
 
Harry
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      10-12-2006
Good Day,

Is there a way to print 8 bytes in a line in a file using
fprintf...like this

12 76 89 76 86 34 98 08
A4..............................

 
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Richard Heathfield
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      10-12-2006
Harry said:

> Good Day,
>
> Is there a way to print 8 bytes in a line in a file using
> fprintf...like this
>
> 12 76 89 76 86 34 98 08
> A4..............................


Nope. But of course you can do something like this:

int ch;
int i = 0;
while((ch = getc(fpin)) != EOF)
{
fprintf(fpout, " %02X", ch);
if(++i % 8 == 0)
{
i = 0;
putc('\n', fpout);
}
}
if(i > 0)
{
putc('\n', fpout);
}


--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)
 
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=?ISO-8859-1?Q?=22Nils_O=2E_Sel=E5sdal=22?=
Guest
Posts: n/a
 
      10-12-2006
Richard Heathfield wrote:
> Harry said:
>
>> Good Day,
>>
>> Is there a way to print 8 bytes in a line in a file using
>> fprintf...like this
>>
>> 12 76 89 76 86 34 98 08
>> A4..............................

>
> Nope. But of course you can do something like this:

Well - one could read 8 bytes, and do
fprintf(fpout, "%02X %02X %02X %02X %02X %02X %02X %02X\n",
buf[0],buf[1],buf[2],buf[3],buf[4],buf[5],buf[6],buf[7]);

Assuming he wanted a hexadecimal representation of each
of the individual byte values.



> int ch;
> int i = 0;
> while((ch = getc(fpin)) != EOF)
> {
> fprintf(fpout, " %02X", ch);
> if(++i % 8 == 0)
> {
> i = 0;
> putc('\n', fpout);
> }
> }
> if(i > 0)
> {
> putc('\n', fpout);
> }

 
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Richard Heathfield
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      10-12-2006
"Nils O. Selåsdal" said:

> Richard Heathfield wrote:
>> Harry said:
>>
>>> Good Day,
>>>
>>> Is there a way to print 8 bytes in a line in a file using
>>> fprintf...like this
>>>
>>> 12 76 89 76 86 34 98 08
>>> A4..............................

>>
>> Nope. But of course you can do something like this:

> Well - one could read 8 bytes, and do
> fprintf(fpout, "%02X %02X %02X %02X %02X %02X %02X %02X\n",
> buf[0],buf[1],buf[2],buf[3],buf[4],buf[5],buf[6],buf[7]);


....er, oh yeah, so he can.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)
 
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CBFalconer
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Posts: n/a
 
      10-12-2006
Richard Heathfield wrote:
> Harry said:
>
> > Is there a way to print 8 bytes in a line in a file using
> > fprintf...like this
> >
> > 12 76 89 76 86 34 98 08
> > A4..............................

>
> Nope. But of course you can do something like this:
>
> int ch;
> int i = 0;
> while((ch = getc(fpin)) != EOF)
> {
> fprintf(fpout, " %02X", ch);
> if(++i % 8 == 0)
> {
> i = 0;
> putc('\n', fpout);
> }
> }
> if(i > 0)
> {
> putc('\n', fpout);
> }


How about:

char b[8];
...
fprintf(fpout, "%02x", b[0]);
for (i = 1, i < 8; i++) fprintf(fpout, " %02x", b[i]);
putc(fpout, '\n');

or

fprintf(fpout, "%02x %02x %02x %02x %02x %02x %02x %02x\j",
b[0], b[1], b[2], b[3], b[4], b[5], b[6], b[7]);

--
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Christopher Benson-Manica
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      10-12-2006
Richard Heathfield <(E-Mail Removed)> wrote:

> > Well - one could read 8 bytes, and do
> > fprintf(fpout, "%02X %02X %02X %02X %02X %02X %02X %02X\n",
> > buf[0],buf[1],buf[2],buf[3],buf[4],buf[5],buf[6],buf[7]);


> ...er, oh yeah, so he can.


Yes, but what about the (likelier) case where the file has a number of
bytes that isn't a multiple of 8? Your original version handled that
easily; the suggested version less so. I'm presuming, possibly
incorrectly, that fprintf() is expensive relative to sprintf(), so
perhaps something like this would be good (criticisms welcome):

#include <stdio.h>
#include <assert.h>

#define BYTES_PER_LINE 8

int main( int argc, char *argv[] )
{
char outbuf[3*BYTES_PER_LINE+1], *bufptr;
int inchar, count=0;
FILE *fpin, *fpout;

assert( argc > 2 );
assert( (fpin = fopen(argv[1],"r")) != NULL );
assert( (fpout = fopen(argv[2],"w")) != NULL );
bufptr = outbuf;
while( (inchar=fgetc(fpin)) != EOF ) {
bufptr += sprintf( bufptr, "%02X ", inchar ); /* assume success */
if( ++count % BYTES_PER_LINE == 0 ) {
*(bufptr-1)='\n';
fputs( outbuf, fpout );
bufptr = outbuf;
}
}
if( bufptr != outbuf ) {
*(bufptr-1)='\n';
fputs( outbuf, fpout );
}
assert( !fclose(fpin) );
assert( !fclose(fpout) );
return 0;
}

--
C. Benson Manica | I *should* know what I'm talking about - if I
cbmanica(at)gmail.com | don't, I need to know. Flames welcome.
 
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Richard Heathfield
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Posts: n/a
 
      10-12-2006
Christopher Benson-Manica said:

> Richard Heathfield <(E-Mail Removed)> wrote:
>
>> > Well - one could read 8 bytes, and do
>> > fprintf(fpout, "%02X %02X %02X %02X %02X %02X %02X %02X\n",
>> > buf[0],buf[1],buf[2],buf[3],buf[4],buf[5],buf[6],buf[7]);

>
>> ...er, oh yeah, so he can.

>
> Yes, but what about the (likelier) case where the file has a number of
> bytes that isn't a multiple of 8? Your original version handled that
> easily;


Naturellement...

> the suggested version less so.


....mais, m'sieur, le question originale ne called pas for une solution
generale. Il merely required pour huit bytes to be ecri a stdout, oui?

> I'm presuming, possibly
> incorrectly, that fprintf() is expensive relative to sprintf(), so
> perhaps something like this would be good (criticisms welcome):
>
> #include <stdio.h>
> #include <assert.h>
>
> #define BYTES_PER_LINE 8
>
> int main( int argc, char *argv[] )
> {
> char outbuf[3*BYTES_PER_LINE+1], *bufptr;


I'd be tempted to make the "bytes per line" value configurable at runtime.

> int inchar, count=0;
> FILE *fpin, *fpout;
>
> assert( argc > 2 );
> assert( (fpin = fopen(argv[1],"r")) != NULL );
> assert( (fpout = fopen(argv[2],"w")) != NULL );


Three consecutive poor uses of assert. (I suspect you know this. I'm merely
heads-upping for newbies' benefit.)

> bufptr = outbuf;
> while( (inchar=fgetc(fpin)) != EOF ) {
> bufptr += sprintf( bufptr, "%02X ", inchar ); /* assume success */
> if( ++count % BYTES_PER_LINE == 0 ) {
> *(bufptr-1)='\n';


Does that overwrite the null terminator? I haven't checked, and perhaps it
doesn't, but the safety of the code is not obvious at a (cursory) glance.

> fputs( outbuf, fpout );
> bufptr = outbuf;
> }
> }
> if( bufptr != outbuf ) {
> *(bufptr-1)='\n';
> fputs( outbuf, fpout );
> }
> assert( !fclose(fpin) );
> assert( !fclose(fpout) );


Two more poor uses of assert. If you must do this, spin them around. If you
can't close the input file, it would be good to at least have had a stab at
closing the output file before the abort.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)
 
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Rod Pemberton
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Posts: n/a
 
      10-13-2006

"Christopher Benson-Manica" <(E-Mail Removed)> wrote in message
news:eglfn4$smh$(E-Mail Removed)...
> Richard Heathfield <(E-Mail Removed)> wrote:
>
> > > Well - one could read 8 bytes, and do
> > > fprintf(fpout, "%02X %02X %02X %02X %02X %02X %02X %02X\n",
> > > buf[0],buf[1],buf[2],buf[3],buf[4],buf[5],buf[6],buf[7]);

>
> > ...er, oh yeah, so he can.

>
> Yes, but what about the (likelier) case where the file has a number of
> bytes that isn't a multiple of 8? Your original version handled that
> easily; the suggested version less so. I'm presuming, possibly
> incorrectly, that fprintf() is expensive relative to sprintf(), so
> perhaps something like this would be good (criticisms welcome):
>


In that case, you'd use fread() with the size of a fixed buffer. fread()
will return the quantity read. This will either be the size of the buffer,
or a smaller quantity. So, you need two printing loops: one for the entire
buffer, and one for the remaining bytes. Both of which have been shown.


Rod Pemberton


 
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Tak-Shing Chan
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Posts: n/a
 
      10-13-2006
On Fri, 13 Oct 2006, Rod Pemberton wrote:

>
> "Christopher Benson-Manica" <(E-Mail Removed)> wrote in message
> news:eglfn4$smh$(E-Mail Removed)...
>> Richard Heathfield <(E-Mail Removed)> wrote:
>>
>>>> Well - one could read 8 bytes, and do
>>>> fprintf(fpout, "%02X %02X %02X %02X %02X %02X %02X %02X\n",
>>>> buf[0],buf[1],buf[2],buf[3],buf[4],buf[5],buf[6],buf[7]);

>>
>>> ...er, oh yeah, so he can.

>>
>> Yes, but what about the (likelier) case where the file has a number of
>> bytes that isn't a multiple of 8? Your original version handled that
>> easily; the suggested version less so. I'm presuming, possibly
>> incorrectly, that fprintf() is expensive relative to sprintf(), so
>> perhaps something like this would be good (criticisms welcome):
>>

>
> In that case, you'd use fread() with the size of a fixed buffer. fread()
> will return the quantity read. This will either be the size of the buffer,
> or a smaller quantity. So, you need two printing loops: one for the entire
> buffer, and one for the remaining bytes. Both of which have been shown.


In theory one could also use Duff's device:

int n = (count + 7) / 8;

switch (count % {
case 0: do { printf("%02X ", *from++);
case 7: printf("%02X ", *from++);
case 6: printf("%02X ", *from++);
case 5: printf("%02X ", *from++);
case 4: printf("%02X ", *from++);
case 3: printf("%02X ", *from++);
case 2: printf("%02X ", *from++);
case 1: printf("%02X ", *from++);
putchar('\n');
} while (--n > 0);
}

Tak-Shing
 
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Christopher Benson-Manica
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      10-13-2006
Richard Heathfield <(E-Mail Removed)> wrote:

> ...mais, m'sieur, le question originale ne called pas for une solution
> generale. Il merely required pour huit bytes to be ecri a stdout, oui?


Ah, le Francais, le langue d'amour! It sounds like you remember as
much of it as I do (Tu as raison.)

> I'd be tempted to make the "bytes per line" value configurable at runtime.


A rare time to give oneself over to the seductive whisperings of
temptation with nary a pang of guilt...

> Three consecutive poor uses of assert. (I suspect you know this. I'm merely
> heads-upping for newbies' benefit.)


Right, they were quick cover-my-bases hacks.

> > while( (inchar=fgetc(fpin)) != EOF ) {
> > bufptr += sprintf( bufptr, "%02X ", inchar ); /* assume success */
> > if( ++count % BYTES_PER_LINE == 0 ) {
> > *(bufptr-1)='\n';


> Does that overwrite the null terminator? I haven't checked, and perhaps it
> doesn't, but the safety of the code is not obvious at a (cursory) glance.


No, bufptr points to the null terminator, assuming per the comment
that sprintf() doesn't do anything unexpected; the code overwrites
the last space in the string. The fact that it wasn't obvious to
you probably means it isn't the best plan, but it does work.

> Two more poor uses of assert. If you must do this, spin them around. If you
> can't close the input file, it would be good to at least have had a stab at
> closing the output file before the abort.


Agreed, thank you.

--
C. Benson Manica | I *should* know what I'm talking about - if I
cbmanica(at)gmail.com | don't, I need to know. Flames welcome.
 
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