Hi,

I'm reading in a WORD (2 bytes) from a binary file. I can display the Hex format of that value without a problem, but I would also like to display the String value of that WORD variable. It's the first 2 bytes of a file, which contains the "magic number" of the file.

I would like my program to output the following:

-----------------
Header Section
header.ID (5348h = "HS")
...
-----------------

2009/10/23 Graeme Geldenhuys :

Hi, I'm reading in a WORD (2 bytes) from a binary file. I can display the

As I pressed the Send button, I thought about trying the following. And it worked! But is this the best way of doing what I want?

type
  TWord = record
    b1: Char;
    b2: Char;
  end;
var
  w: TWord;
  s: string;
begin
  w := TWord(hdr^.ID);
  s := w.b1 + w.b2;
  writeln(s);
end;

w: WORD
...
YourString := Chr(Lo(w)) + Chr(Hi(w))
or
YourString := Chr(Hi(w)) + Chr(Lo(w))

(depending on endianness)

2009/10/23 Aleksa Todorovic :

Ah, thanks. I was close, I used High() and Low() instead. :-( Dope!

Personally, I'd do something like this, as it is more explicit (you won't be left wondering what "magic" occurred later:

function WordToString(w: word): String;
begin
 Result := Char(hi(w)) + Char(lo(w));
end;

That's dangerous, though, if your magic number's two bytes aren't printable ASCII. I believe there is an RTL function like IsPrintableASCII or something like that that you could check each character with.

Jeff.

Jeff Wormsley wrote

That's dangerous, though, if your magic number's two bytes aren't printable

That should never be a problem for my tool though. The tool I am writing is specific to the INF help format. The tool dumps the file structure to a text file. (I need this for debugging purposes)

When my app processes a file, it reads the first 155 bytes (header information), then does a numerical check of the magic number in the header. If it's an unknown value, it stops right there. If it's a known value, it continues at which point it starts outputing the text to file.

Jeff Wormsley wrote

Oh, I was fairly certain of that. Its just these little routines tend to end up in libraries of handy code. I tend to be overly cautious with some of these because of that.

Point taken. :-) This code is purposely rewritten and totally standalone so I can track down a bug in my actual project, the INF DocView project.

Wouldn't it be more direct to use

Blockwrite(<file>,header.ID,sizeof(header.ID));

That would make it robust against changes of ID size and would avoid the many type castings.

Jürgen Hestermann wrote

Wouldn't it be more direct to use Blockwrite(<file>,header.ID,sizeof(header.ID));

I read the complete header structure in one go (155 bytes). I simply want to output to a text file, a human readable structure of the complete INF file. The INF file format is quite complex and one can easily get confuse between various bits of information all in various locations inside the file.

The tool I am writing is imply so I can see in a more visual way the various bits of information, without the need for a hex editor etc... So the solution described earlier will suffice for my needs.

You can consider declaring the ID in the header record type as array[1..2] of char.

Vincent

In our previous episode, Vincent Snijders said:

(starting to use ansichar might not be bad)

Vincent Snijders wrote

You can consider declaring the ID in the header record type as array[1..2] of char.

As Marco suggested... Char size might not always be the same. I did however change my header to array[0..1] of byte instead.

Good point. But I preferred to go with array of Byte.

But then you still cannot do:

if header.id='HS' then
   // magic is correct.

That is why I proposed a static array of char.

Vincent

2009/10/24 Vincent Snijders :

No, but I can do this... which is sufficient.

var
  s: string
begin
  s := hdr^.ID;
  if S = "HS" then
    ...

Not with fpc, I guess, otherwise I learned two new features:
* string constants that are surrounded with double quotes
* assignment to static array of byte to a string without conversion

What type is ID?

Vincent

As Marco suggested... Char size might not always be the same.

Why that? I hope noone changes the meaning of such long-time types some day. If a new type is needed, then it should get a new name too.

In our previous episode, Jürgen Hestermann said:

> As Marco suggested... Char size might not always be the same. Why that? I hope noone changes the meaning of such long-time types some day. If a new type is needed, then it should get a new name too.

Codegear did this with Delphi 2009 in August 2008, forcing to check all string code.

However FPC will probably only add a Delphi2009 mode, and code in the current modes will remain working.

----- Original Message -----

Doesn't String[2] imply a length byte followed by 2 bytes for content = 3 bytes for a Pascal string? Even a C string of two characters content is 3 bytes.

Just my $.03

Gary

----- Original Message -----