binary data conversion

**Martin Ambuhl** · Nov 14 '05, 05:28 AM

Re: binary data conversion

Drake wrote:
[color=blue]
> Well, I'm stuck in legacy land and I need a helping hand.
>
> We're trying to give some modern value-added functionality to
> a circa-1985 fortran proggie.
>
> The program produces a binary file, by itself no problem...
> each record needs to be converted into std::vector<mys truct>[/color]

Bummer. Ask C++ questions in a C++ newsgroup like news:comp.lang. c++

**Mike Wahler** · Nov 14 '05, 05:28 AM

Re: binary data conversion

"Drake" <x@y.net> wrote in message
news:Xns94C7AF6 EC57AEnomailcom @207.217.125.20 4...[color=blue]
> Well, I'm stuck in legacy land and I need a helping hand.
>
> We're trying to give some modern value-added functionality to
> a circa-1985 fortran proggie.
>
> The program produces a binary file, by itself no problem...
> each record needs to be converted into std::vector<mys truct>
> I'm having a helluva time with the binary-->(pod)datatyp e conversion.
>
> Although I've referred to C++ containers, iostreams
> are not used... FILE* only. Insert/extract operators are not an option.
>
> Here's 3 records (broken into lines for easy reading)...
>
> D5840000428F000 0140501000B0000 000000
> 993A000066C7000 0140501000F0000 000000
> C0880000538D010 0140501001D0000 000000
>
> Here's (pod) mystruct...
>
> static struct IDX_RECORD /* length 18 bytes */
> {
> unsigned long respnum; // 4 bytes
> unsigned long datfile_offset; // 4 bytes
> unsigned char disposition; // 1 byte
> unsigned char status; // 1 byte
> unsigned char segment_svd; // 1 byte
> unsigned char not_used; // 1 byte
> unsigned short segment_dupr; // 2 bytes
> unsigned long next_segment_of fset; // 4 bytes
> };[/color]

I'll assume those byte sizes in your comments refer
to your particular implementation. The language
doesn't require those sizes (but it does require
minimum sizes).
[color=blue]
>
> Is this one of those times fscanf IS the "better" (whatever that means)[/color]
way?[color=blue]
>
> Assuming the powers have big-time aversion to "scan" functions,
> what's an alternative?[/color]

fscanf() is not what you need. It reads textual data.

Use fread(). And be sure to account for 'endianness'.

-Mike

**Mac** · Nov 14 '05, 05:28 AM

Re: binary data conversion

On Sun, 11 Apr 2004 00:14:44 +0000, Drake wrote:
[color=blue]
> Well, I'm stuck in legacy land and I need a helping hand.
>
> We're trying to give some modern value-added functionality to
> a circa-1985 fortran proggie.
>
> The program produces a binary file, by itself no problem...
> each record needs to be converted into std::vector<mys truct>
> I'm having a helluva time with the binary-->(pod)datatyp e conversion.
>
> Although I've referred to C++ containers, iostreams
> are not used... FILE* only. Insert/extract operators are not an option.
>
> Here's 3 records (broken into lines for easy reading)...
>
> D5840000428F000 0140501000B0000 000000
> 993A000066C7000 0140501000F0000 000000
> C0880000538D010 0140501001D0000 000000[/color]

Is this a hex dump of the file, or is the file text... You said it was
binary earlier.
[color=blue]
>
> Here's (pod) mystruct...
>
> static struct IDX_RECORD /* length 18 bytes */
> {
> unsigned long respnum; // 4 bytes
> unsigned long datfile_offset; // 4 bytes
> unsigned char disposition; // 1 byte
> unsigned char status; // 1 byte
> unsigned char segment_svd; // 1 byte
> unsigned char not_used; // 1 byte
> unsigned short segment_dupr; // 2 bytes
> unsigned long next_segment_of fset; // 4 bytes
> };
>
> Is this one of those times fscanf IS the "better" (whatever that means) way?
>[/color]

Well, if the file is text, I think fscanf() is probably the best way, but
you can do whatever you want, including reading a character at a time with
getc() and not calling any other library functions. Another function to
consider is fgets() (again, assuming a text file.)

If the file is binary, which is what you said initially, I definitely
would not use fscanf(). I would use getc() or fread().
[color=blue]
> Assuming the powers have big-time aversion to "scan" functions,
> what's an alternative?
>[/color]

What do you mean by "powers?" Is that short for "powers that be," meaning,
loosely, whoever is in charge?
[color=blue]
> Thank you for your thoughts,
> Drake[/color]

I think you may want comp.lang.c++.

If you want a c solution, I suggest you rephrase to make that more clear,
removing all reference to c++, just to be safe, and repost.

If you want a c++ solution, post in comp.lang.c++, but read their faq
and/or lurk first to make sure you don't annoy anyone.

--Mac

**Drake** · Nov 14 '05, 05:28 AM

Re: binary data conversion

Martin Ambuhl <mambuhl@earthl ink.net> wrote in news:c5a47k$2m9 rj0$3@ID-
227552.news.uni-berlin.de:
[color=blue]
> Drake wrote:
>[color=green]
>> Well, I'm stuck in legacy land and I need a helping hand.
>>
>> We're trying to give some modern value-added functionality to
>> a circa-1985 fortran proggie.
>>
>> The program produces a binary file, by itself no problem...
>> each record needs to be converted into std::vector<mys truct>[/color]
>
> Bummer. Ask C++ questions in a C++ newsgroup like news:comp.lang. c++[/color]

A few lines later the post tried and obviously failed in avoiding this
answer.

<< Although I've referred to C++ containers, iostreams
<< are not used... FILE* only. Insert/extract operators are not an
<< option.

Anyway std::vector isn't the problem. It's the conversion.

Drake

**Dilton McGowan II** · Nov 14 '05, 05:28 AM

Re: binary data conversion

"Drake" <x@.y.net> wrote in message
news:Ju3ec.4494 $k05.1243@newsr ead2.news.pas.e arthlink.net...[color=blue]
> Martin Ambuhl <mambuhl@earthl ink.net> wrote in news:c5a47k$2m9 rj0$3@ID-
> 227552.news.uni-berlin.de:
>[color=green]
> > Drake wrote:
> >[color=darkred]
> >> Well, I'm stuck in legacy land and I need a helping hand.
> >>
> >> We're trying to give some modern value-added functionality to
> >> a circa-1985 fortran proggie.
> >>
> >> The program produces a binary file, by itself no problem...
> >> each record needs to be converted into std::vector<mys truct>[/color]
> >
> > Bummer. Ask C++ questions in a C++ newsgroup like news:comp.lang. c++[/color]
>
>
> A few lines later the post tried and obviously failed in avoiding this
> answer.
>
> << Although I've referred to C++ containers, iostreams
> << are not used... FILE* only. Insert/extract operators are not an
> << option.
>
> Anyway std::vector isn't the problem. It's the conversion.
>
>
> Drake[/color]

Tastefully dispatched. ;-)

**Malcolm** · Nov 14 '05, 05:28 AM

Re: binary data conversion

"Drake" <x@y.net> wrote in message[color=blue]
>
> Here's 3 records (broken into lines for easy reading)...
>
> D5840000428F000 0140501000B0000 000000
> 993A000066C7000 0140501000F0000 000000
> C0880000538D010 0140501001D0000 000000
>
> Here's (pod) mystruct...
>
> static struct IDX_RECORD /* length 18 bytes */
> {
> unsigned long respnum; // 4 bytes
> unsigned long datfile_offset; // 4 bytes
> unsigned char disposition; // 1 byte
> unsigned char status; // 1 byte
> unsigned char segment_svd; // 1 byte
> unsigned char not_used; // 1 byte
> unsigned short segment_dupr; // 2 bytes
> unsigned long next_segment_of fset; // 4 bytes
> };
>
> Assuming the powers have big-time aversion to "scan" functions,
> what's an alternative?
>[/color]
As someone else has pointed out, you don't say whether your example is a
hexdump or a text file. fscanf() is useful only for text files, but of
limited utlity if numerics are not separated by delimiters.

What you need are the functions

unsigned long read32us(FILE *fp);
unsigned short read16us(FILE *fp);

If you want to use C++ you can be ugly and replace the FILE * with a stream,
or be object-oriented and derive a class from iostream with the functions
added.
In either case, build the read32() function on top of fgetc() / character
extraction.
If you are using C++, throw exceptions in the case of premature EOF.

**Thomas Matthews** · Nov 14 '05, 05:29 AM

Re: binary data conversion

Drake wrote:
[color=blue]
> Well, I'm stuck in legacy land and I need a helping hand.
>
> We're trying to give some modern value-added functionality to
> a circa-1985 fortran proggie.
>
> The program produces a binary file, by itself no problem...
> each record needs to be converted into std::vector<mys truct>
> I'm having a helluva time with the binary-->(pod)datatyp e conversion.
>
> Although I've referred to C++ containers, iostreams
> are not used... FILE* only. Insert/extract operators are not an option.
>
> Here's 3 records (broken into lines for easy reading)...
>
> D5840000428F000 0140501000B0000 000000
> 993A000066C7000 0140501000F0000 000000
> C0880000538D010 0140501001D0000 000000
>
> Here's (pod) mystruct...
>
> static struct IDX_RECORD /* length 18 bytes */
> {
> unsigned long respnum; // 4 bytes
> unsigned long datfile_offset; // 4 bytes
> unsigned char disposition; // 1 byte
> unsigned char status; // 1 byte
> unsigned char segment_svd; // 1 byte
> unsigned char not_used; // 1 byte
> unsigned short segment_dupr; // 2 bytes
> unsigned long next_segment_of fset; // 4 bytes
> };
>
> Is this one of those times fscanf IS the "better" (whatever that means) way?
>
> Assuming the powers have big-time aversion to "scan" functions,
> what's an alternative?
>
> Thank you for your thoughts,
> Drake[/color]

If your file is ASCII encoded hex file (a.k.a. Hex dump),
then you may want to read each line using fgets(), then
fill in your data structure by converting the ASCII values
into native formats. This is probably the faster method
than fscanf.

If the file is actually binary, you may want to use the
fread function and read a block into a buffer then load
the fields of your structure from the buffer.

In no case do you want to load your structure directly
from the file or memory. The simple rule is that the
size of a structure may not be equal to the size of its
members. The compiler is allowed to add "padding" bytes
between members. This is what kills most programs that
attempt to map a structure directly to an input stream.

--
Thomas Matthews

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