Board index » cppbuilder » size of a const at compile time

2006-03-28 02:18:16 AM
cppbuilder61
Hello,
At the moment (well for many years) I have following code:
#define MAX_LEN_TITLE 20
const u_8* blank_title = (u_8*)" ";
Where blank_title is just a string to clear a title on a form (embedded
system). The annoying thing is of course when I have to do a maintenance
and for example a customer wants a title length of 22. Then I have to
change also the const declaration.
Not a big deal of course, but can this also automatically happen at
compile time ? For example:
const u_8 blank_title[MAX_LEN_TITLE + 1] ... euh but how to fill it with
blanks at compile time ?
of course another solution would be to make it a variable in the pool,
but I like to have it in EPROM as I have not much spare memory.
--
rgds, Wilfried
www.mestdagh.biz
 

"Wilfried Mestdagh" < XXXX@XXXXX.COM >wrote in message
be easier?
--
Bruce
 

" Bruce Salzman" < XXXX@XXXXX.COM >writes:
 

{smallsort}

Wilfried Mestdagh < XXXX@XXXXX.COM >writes:
enum
{
MAX_LEN_TITLE = 20
};
makes MAX_LEN_TITLE a well-behaved name.
" " is of type 'array of 21 char const'. Why do you
first cast it to 'pointer to u_8 (non-const)' (whatever u_8 is) and then
to 'pointer to u_8 const'?
What's wrong with
char const blank_title[] = " ";
char const longer_blank_title[] = " ";
enum
{
MAX_LEN_TITLE = sizeof longer_blank_title
/ sizeof longer_blank_title[0];
};
If MAX_LEN_TITLE has to be defined independently of blank_title, you
could use a BOOST_STATIC_ASSERT
(cf. www.boost.org/doc/html/boost_staticassert.html) to make
sure that blank_title has the correct length. This doesn't fill
blank_title, but the compiler will tell you when to adjust its
filling.
 

Hi Thomas,
change is needed.
--
rgds, Wilfried
www.mestdagh.biz
 

Thomas Maeder [TeamB] wrote:
null string to the screen at the given position it will write nothing
and the characters are still visible. This is not PC, it is embedded system.
--
rgds, Wilfried
www.mestdagh.biz
 

Wilfried Mestdagh wrote:
memset(form_title, ' ', MAX_LEN_TITLE);
?
Tom
 

"Wilfried Mestdagh" < XXXX@XXXXX.COM >wrote in message
Rufus
 

Wilfried Mestdagh < XXXX@XXXXX.COM >writes:
enum
{
MAX_LEN_TITLE = (sizeof longer_blank_title
/ sizeof longer_blank_title[0])
- 1; // don't count the terminating 0 character
};
is probably better than the version quoted above.
 

Hi Tom,
all these RTL functions are unusable. Also it cost unneeded CPU time
because it can be in eprom.
--
rgds, Wilfried
www.mestdagh.biz
 

Wilfried Mestdagh wrote:
is just a string to clear a title on a form (embedded system)." Do you
have to copy the string to a fixed address, or can you just reassign the
title pointer? E.g. can you just do:
form_title = blank_title;
or do you need the equivalent of:
memcpy(form_title, blank_title, MAX_LEN_TITLE);
Incidentally, the embedded compiler I've used (GCC on QNX), has memset
as an intrinsic - no RTL required.
Tom
 

Wilfried Mestdagh wrote:
found a way to do it.
If you want to do it bad enough, you can do this in TASM.
.dataseg
public _title
public _blank_title
_title db 'This is the title',0
MAX_LEN_TITLE equ (LENGTH _title) -1
_blank_title db MAX_LEN_TITLE dup(' '),0
Or leave off the ,0 and -1 if you don't need zero-terminated strings.
 

Hi Bob,
Yes also good idea. thx.
--
rgds, Wilfried
www.mestdagh.biz
 

Hi Tom,
I want to thank you for your help, but we are not on my question
anymore. My mothers tongue is not English so my question was probably
not very clear, as also the names of the variables.
I just needed to have a constant in eprom filled with blanks and a
certain length wich are answered by Thomas and Bob.
As for the application, I need to clear a displays title which only can
be done to overwrite the screen locations with blanks. So there fore I
need the constant which has to have the length of the longest title.
--
rgds, Wilfried
www.mestdagh.biz