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digitalmars.D - printf/scanf extensions

reply Sean Kelly <sean f4.ca> writes:
I've been working on a scanf implementation as part of my stream mods, and I've
started wondering about D-specific extensions.  I've already added support for
the %.*s parameter for D strings, and have started to think about complex and
imaginary numbers.  Should I even bother trying to parse "A + Bi" as a single
number or should the user be expected to call scanf( "%f + %fi", cd.re, cd.im )
to parse this type of thing?


Sean
Jun 29 2004
next sibling parent Ben Hinkle <bhinkle4 juno.com> writes:
Sean Kelly wrote:


 I've been working on a scanf implementation as part of my stream mods, and
 I've
 started wondering about D-specific extensions.  I've already added support
 for the %.*s parameter for D strings, and have started to think about
 complex and
 imaginary numbers.  Should I even bother trying to parse "A + Bi" as a
 single number or should the user be expected to call scanf( "%f + %fi",
 cd.re, cd.im ) to parse this type of thing?


One advantage of a builtin complex support would be handling negative values
for B and zero for A. Otherwise if the code had scanf("%f + %fi") then
users would have to enter, for example, 0+-2i instead of the more natural
-2i. So I'd say go for it. I don't know if any other printf extension has
done this already - if there were we could check out their syntax. Off the
top of my head the format character "j" could be used - and "j" is commonly
used in engineering as the imaginary unit so it is a natural choice. That
would mean "%j" would parse a cfloat, "%lj" a cdouble and "%Lj" a creal. By
"parse" it would accept numbers of the form
 %f %fi
 %fi
 %f %fj
 %fj



 
 Sean
Jun 29 2004
prev sibling parent reply "Walter" <newshound digitalmars.com> writes:
I'm working on a replacement for printf, so don't bother with that <g>.

"Sean Kelly" <sean f4.ca> wrote in message
news:cbt0je$d8r$1 digitaldaemon.com...

 I've been working on a scanf implementation as part of my stream mods, and


I've

 started wondering about D-specific extensions.  I've already added support


for

 the %.*s parameter for D strings, and have started to think about complex


and

 imaginary numbers.  Should I even bother trying to parse "A + Bi" as a


single

 number or should the user be expected to call scanf( "%f + %fi", cd.re,


cd.im )

 to parse this type of thing?


 Sean
Jun 29 2004
parent reply Sean Kelly <sean f4.ca> writes:
In article <cbtik8$183l$1 digitaldaemon.com>, Walter says...

I'm working on a replacement for printf, so don't bother with that <g>.


That's what inspired me to ask this question :)  By the way, I've been mulling
over the width specifier and dealing with it seems like kind of a pain.  Assume
I have a file containing this:

-123 0x456

and I do this:

scanf( "%1i%i %2i%i", &a, &b, &c, &d );

The way I read the spec, I think I would end up with this:

a: 0
b: 123
c: 0
d: 456 (base 10)

Is this correct?  It seems odd that creative use of the width specifier can
cause a sign or base specifier to be lost.  I've even considered throwing some
kind of exception when this happens, but haven't decided whether that would be a
good idea.  On the other hand, I'm sure the optional sign and such need to be
counted as part of the value width (they're not in the current stream
implementation) since the specifier is meant to allow reads from fixed-width
files.


Sean
Jun 30 2004
parent reply "Walter" <newshound digitalmars.com> writes:
"Sean Kelly" <sean f4.ca> wrote in message
news:cbuvj5$tm3$1 digitaldaemon.com...

 In article <cbtik8$183l$1 digitaldaemon.com>, Walter says...

I'm working on a replacement for printf, so don't bother with that <g>.


 That's what inspired me to ask this question :)  By the way, I've been


mulling

 over the width specifier and dealing with it seems like kind of a pain.


Assume

 I have a file containing this:

 -123 0x456

 and I do this:

 scanf( "%1i%i %2i%i", &a, &b, &c, &d );

 The way I read the spec, I think I would end up with this:

 a: 0
 b: 123
 c: 0
 d: 456 (base 10)

 Is this correct?  It seems odd that creative use of the width specifier


can

 cause a sign or base specifier to be lost.  I've even considered throwing


some

 kind of exception when this happens, but haven't decided whether that


would be a

 good idea.  On the other hand, I'm sure the optional sign and such need to


be

 counted as part of the value width (they're not in the current stream
 implementation) since the specifier is meant to allow reads from


fixed-width

 files.


I think the 'x' where a number is expected would/should cause an error.
Jun 30 2004
parent Sean Kelly <sean f4.ca> writes:
In article <cbv8fu$1alf$2 digitaldaemon.com>, Walter says...

I think the 'x' where a number is expected would/should cause an error.


Oops, good point.  So it's only the sign char and leading '0' for octal numbers
that might cause problems.  I guess then, width<=2 for %i could do weird things
or width=1 for any integer type.  I'm going to ignore the problem for now as the
standard doesn't seem to care, but will perhaps revisit it if I decide to start
throwing exceptions out of scanf.

Sean
Jun 30 2004