www.digitalmars.com         C & C++   DMDScript  

D - Bug in printf function?

reply "Bruno A. Costa" <bruno codata.com.br> writes:
Hi,

The following code fails to produce the expected result:

// ====================================

import std.string;

int main (char[][] args)
{
        byte bt = 0;
        printf (toString (bt));

        return 0;
}
// ====================================

The printf function should display the string "0", but it shows the sequence
"0123456789". The same thing occurs if I change the value of variable bt to
any number less than 10.

The problem *does not occur* if I concatenate the value returned from
toString with other string:

printf ("Value = " ~ toString(bt)); // Displays "Value = 0" correctly

I am using dmd 0.82 and gcc 3.2.3

cheers.

Bruno.
Apr 26 2004
next sibling parent reply J Anderson <REMOVEanderson badmama.com.au> writes:
Bruno A. Costa wrote:


Hi,

The following code fails to produce the expected result:

// ====================================

import std.string;

int main (char[][] args)
{
        byte bt = 0;
        printf (toString (bt));

        return 0;
}
// ====================================
  



printf as well.

As a workaround (if it is a bug), you can go:
 printf (toString (bt).dup);


-- 
-Anderson: http://badmama.com.au/~anderson/
Apr 26 2004
parent reply Ant <Ant_member pathlink.com> writes:
In article <c6ivk0$2roe$1 digitaldaemon.com>, J Anderson says...

Bruno A. Costa wrote:


Hi,

The following code fails to produce the expected result:

// ====================================

import std.string;

int main (char[][] args)
{
        byte bt = 0;
        printf (toString (bt));

        return 0;
}
// ====================================
  



printf as well.

As a workaround (if it is a bug), you can go:
 printf (toString (bt).dup);



(I don't have D here)

will it print correctly with 
printf (toString (bt)~'\0');   // or "\0"
?

Ant
Apr 26 2004
parent J Anderson <REMOVEanderson badmama.com.au> writes:
Ant wrote:


(I don't have D here)

will it print correctly with 
printf (toString (bt)~'\0');   // or "\0"
?

Ant



You mean:
 printf (toString (bt) ~ "\0");

Yeah but:
What that's doing is essentially a dup because ~ causes a reallocation 
of the array with a length.  Afterwoods D automatically converts to a 
zero-terminated string any way.  You could add " " on if you wished for 
the same effect.

-- 
-Anderson: http://badmama.com.au/~anderson/
Apr 26 2004
prev sibling next sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Bruno A. Costa wrote:


 Hi,
 
 The following code fails to produce the expected result:




         printf (toString (bt));




Does it work if you do the Right Thing by converting it to a 
null-terminated string?  i.e.

	printf (toStringz(toString(bt)));

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the 
unfortunate victim of intensive mail-bombing at the moment.  Please keep 
replies on the 'group where everyone may benefit.
Apr 26 2004
next sibling parent reply J Anderson <REMOVEanderson badmama.com.au> writes:
Stewart Gordon wrote:


 Does it work if you do the Right Thing by converting it to a 
 null-terminated string?  i.e.

     printf (toStringz(toString(bt)));

 Stewart.




That works but as I explained before that causes a reallocation.  D 
automaticly converts char [] to zero terminated string if you pass it 
into a c char * function.


-- 
-Anderson: http://badmama.com.au/~anderson/
Apr 26 2004
parent Vathix <vathix dprogramming.com> writes:
On Mon, 26 Apr 2004 21:03:02 +0800, J Anderson 
<REMOVEanderson badmama.com.au> wrote:


 Stewart Gordon wrote:


 Does it work if you do the Right Thing by converting it to a 
 null-terminated string?  i.e.

     printf (toStringz(toString(bt)));

 Stewart.




 That works but as I explained before that causes a reallocation.  D 
 automaticly converts char [] to zero terminated string if you pass it 
 into a c char * function.



toStringz() only reallocates if there's not a zero byte past the end. D 
will implicitly convert char[] to char*, but whether or not it's zero 
terminated is up to the caller. This comes up too often ;)


-- 
Christopher E. Miller
Apr 26 2004
prev sibling parent reply "Bruno A. Costa" <bruno codata.com.br> writes:
Stewart Gordon wrote:



 
 Does it work if you do the Right Thing by converting it to a
 null-terminated string?  i.e.
 
 printf (toStringz(toString(bt)));
 
 Stewart.
 



If I do:
        printf (toString (bt).dup);
        printf (toStringz(toString (bt)));

it works.

If I do:
        printf (toString(125)); // numbers >= 10 don't cause problems

it works too, but if I pass a number < 10:

        printf (toString(5)); // Error: shows 56789 instead of 5.

Note that the problem does not seem to be in toString function, because
concatenated strings are displayed correctly:

        printf ("Value = " ~ toString (5));   // Displays "Value = 5"

Cheers.

Bruno.
Apr 26 2004
next sibling parent Vathix <vathix dprogramming.com> writes:
On Mon, 26 Apr 2004 10:41:13 -0300, Bruno A. Costa <bruno codata.com.br> 
wrote:


 If I do:
         printf (toString (bt).dup);
         printf (toStringz(toString (bt)));

 it works.

 If I do:
         printf (toString(125)); // numbers >= 10 don't cause problems

 it works too, but if I pass a number < 10:

         printf (toString(5)); // Error: shows 56789 instead of 5.

 Note that the problem does not seem to be in toString function, because
 concatenated strings are displayed correctly:

         printf ("Value = " ~ toString (5));   // Displays "Value = 5"

 Cheers.

 Bruno.



D strings aren't always compatible with C strings. They often are, which 
makes it tricky. Why not use the D function stdout.printf() by importing 
std.stream and you won't have to worry about it.


-- 
Christopher E. Miller
Apr 26 2004
prev sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Bruno A. Costa wrote:

<snip>

 If I do:
         printf (toString(125)); // numbers >= 10 don't cause problems
 
 it works too, but if I pass a number < 10:
 
         printf (toString(5)); // Error: shows 56789 instead of 5.




That gives insight into how toString works.  Obviously it has a string 
"0123456789" somewhere, and in order to toString a single digit, it just 
returns a slice of the array.  And the length gets lost in the 
conversion from char[] to char*.

This is also consistent with my experience that slices invariably aren't 
null terminated.  At least if they're not at the end of the string, and 
the string doesn't have an intervening null char in just the right place.

OTOH, if the number >= 10, then it builds up the string rather than just 
cutting a slice.  Which, with the way things are implemented, tends to 
lead to a null termination.

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the 
unfortunate victim of intensive mail-bombing at the moment.  Please keep 
replies on the 'group where everyone may benefit.
Apr 26 2004
parent reply "Walter" <newshound digitalmars.com> writes:
"Stewart Gordon" <smjg_1998 yahoo.com> wrote in message
news:c6j62v$4np$1 digitaldaemon.com...

 That gives insight into how toString works.  Obviously it has a string
 "0123456789" somewhere, and in order to toString a single digit, it just
 returns a slice of the array.  And the length gets lost in the
 conversion from char[] to char*.



You're on to me <g>. One advantage to garbage collection is you don't need
to keep track of what is a malloc'd pointer and what is static, they can be
mixed up. So, since most conversions are just a single digit, it's very fast
to just slice a static array for them. This is one advantage to gc systems
that few gc detractors recognize.
Apr 26 2004
parent reply "Matthew" <matthew.hat stlsoft.dot.org> writes:
"Walter" <newshound digitalmars.com> wrote in message
news:c6jnbk$13o0$1 digitaldaemon.com...

 "Stewart Gordon" <smjg_1998 yahoo.com> wrote in message
 news:c6j62v$4np$1 digitaldaemon.com...

 That gives insight into how toString works.  Obviously it has a string
 "0123456789" somewhere, and in order to toString a single digit, it just
 returns a slice of the array.  And the length gets lost in the
 conversion from char[] to char*.



 You're on to me <g>. One advantage to garbage collection is you don't need
 to keep track of what is a malloc'd pointer and what is static, they can be
 mixed up. So, since most conversions are just a single digit, it's very fast
 to just slice a static array for them. This is one advantage to gc systems
 that few gc detractors recognize.



Yes indeed. Someone needs to point that out in a book sometime, don't you think?
Apr 26 2004
parent "Walter" <newshound digitalmars.com> writes:
"Matthew" <matthew.hat stlsoft.dot.org> wrote in message
news:c6jrgb$1aln$1 digitaldaemon.com...

 "Walter" <newshound digitalmars.com> wrote in message
 news:c6jnbk$13o0$1 digitaldaemon.com...

 "Stewart Gordon" <smjg_1998 yahoo.com> wrote in message
 news:c6j62v$4np$1 digitaldaemon.com...

 That gives insight into how toString works.  Obviously it has a string
 "0123456789" somewhere, and in order to toString a single digit, it










 returns a slice of the array.  And the length gets lost in the
 conversion from char[] to char*.



 You're on to me <g>. One advantage to garbage collection is you don't







 to keep track of what is a malloc'd pointer and what is static, they can







 mixed up. So, since most conversions are just a single digit, it's very







 to just slice a static array for them. This is one advantage to gc







 that few gc detractors recognize.



 Yes indeed. Someone needs to point that out in a book sometime, don't you




LOL!
Apr 26 2004
prev sibling parent "Walter" <newshound digitalmars.com> writes:
"Bruno A. Costa" <bruno codata.com.br> wrote in message
news:c6iumk$2qar$1 digitaldaemon.com...

 Hi,

 The following code fails to produce the expected result:

 // ====================================

 import std.string;

 int main (char[][] args)
 {
         byte bt = 0;
         printf (toString (bt));

         return 0;
 }
 // ====================================

 The printf function should display the string "0", but it shows the




 "0123456789".



That's because toString() creates a D string, whose length is determined by
the ".length" property. printf's first argument takes a 0 terminated string.
To get what you want,

printf("%.*s", toString(bt));    // %.*s will recognize a D string

or:

printf(toStringz(toString(bt)));    // makes a 0 terminated string
Apr 26 2004