New 'n' Improved comp.lang.c FAQ List

[Matthew J. Newhook]

paul at sequoia.cray.com (Paul Dow (CRI-UK)) writes:


>Will this never end.....   Here's my three ha'pence....

>In article <1991Apr4.024300.19969 at garfield.cs.mun.ca>, matthew1 at garfield.cs.mun.ca (Matthew J. Newhook) writes:
[ stuff deleted .. ]
>|> Actually here is a correct (portable) version (assuming that you want to 
>|> keep a static character buffer, and not use a newly malloc'd one each time).
>|> 
>|> #include <math.h>
>|> 
>|> char *itoa(int i)
>|> {
>|>     static int first = 1;
>|>     static char *s;
>|> 
>|>     if (first) { /* IF FIRST TIME ALLOCATE MEMORY FOR STRING */
>|>         first = 0;
>|>         s = (char *) 
>|>         malloc((long) ceil(log10(pow(2, (double) sizeof(int) * 8))) +1);
>|>         if (!s) {
>|>             fprintf(stderr,"malloc failed\n");
>|>             exit(1);
>|>         }
>|>     }
>|> 
>|>     sprintf(s, "%d", i);
>|>     return s;
>|> }
>|> 
>|> This is portable, 'cause it always assigns the correct value to the size of
>|> the array, without depending on the sizeof(int) == 2.
>|> 
>|> Matthew Newhook
>|>         


>It is easy to say that things are "correct" & "portable".  How often have
>people been flamed in this newsgroup (and others) for that.  A lot of people
>are put of replying to questions for fear of being flamed.  Mind you, if
>the replies were framed as suggestions as opposed to "correct"/"portable" etc,
>then they would not irritate the "flamer" so much.

>Anyhow, enough of that sideline, let us look at the last example above and ask
>a few questions ?

>Q1)    The "*8" I presume is for the numbers of bits in a byte.  Are there
>    problems here on a 9 bit machine?  I don't have access to any such                        machines, so I cannot test this out.

>Q2)    Should the first parameter to pow() be a double - the compiler may not
>    support prototypes.

I'm using ANSI C, and the standard says pow takes double.

>Q3)    The "+1" appears to be for the terminating NULL character.  Has any
>    space being allowed for a leading "-" sign ?

woops...

>Q4)    Malloc is being passed a "long" type for the number of bytes.  Should
>    this be an unsigned (int)  [it is on my SunOS 4.1 system].

Should actually be size_t according to the standard.

>Q5)    If the malloc fails, then a string is written to stderr.  Is this
>    accetable?  Is it also acceptable to exit at that point ?
>        This may not be acceptable to some applications which might not support a
>        stderr per se ["stderr" might exist, but is it valid to use it ?].
>    I have encountered this problem with assrted C libraries on several
>    systems.

It was acceptable for this example...

>    I have to admit that it is good to see return values checked.  Code that
>    ignores return values is the bane of my life.

>Suggestions:

>Here are a few things that I would think about.  They would not change the functionality, but may be worth considering - depending on ones viewpoint.

>S1)    I would tend to use a NULL/not NULL test for the pointer to determine if
>    the buffer needed to be allocated.

This is a moot point, IMHO.  "if (!p)" is a common enough expression...

>S2)    It took a bit of thinking about to work out what the
>        malloc((long) ceil(log10(pow(2, (double) sizeof(int) * 8))) +1);
>    was doing.  Can this be simplified ?

I don't know can it?  Any ideas anyone? 
>S3) It took me a second or two to work out where the result of the malloc was 
>     going. It would have helped me of the malloc line was indented more.  
> Possibly, but where else was the malloc going?  
Actually, I think someone posted a better solution to mine later...  
It went like this, if your limits.h defines INT_MIN in the right manner...  
(ie. -2147483648 instead of (1 << 31) or whatever).  And, of course, you 
use ANSI C.

#include <limits.h>
#define QUOTE(a)    #a
char *itoa(int i)
{
    static char retbuf[sizeof(QUOTE(INT_MIN)];
                      ^^^^^^^^ shouldn't there be a +1 here for the null char?
    /*
     * I *think* the above is a legitimate use of sizeof.  Can
     * any standard gurus confirm or deny this?
     */

    (void) sprintf(retbuf, "%d", i);
    return retbuf;
}

Aid.  (adrian at gonzo.mti.com)
>Paul.

>[All disclaimers may be assumed]
Matthew Newhook
-- 
----------------matthew1 at garfield.cs.mun.ca 
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