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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Floating point to string, and back via `%a'...
Date: Wed, 22 Jul 2015 16:52:23 -0700
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Keith Thompson <kst-u@mib.org> writes:
> "Chris M. Thomasson" <nospam@nospam.nospam> writes:
> [...]
>>> It looks like MSVC simply has a bug.  You could calculate the number of
>>> digits you need but that would be fiddly to get right in every single
>>> case.
>>
>> Right. FWIW, %a does not work on MSVC for sscanf always returns zero.
>
> Does MSVC just not implement %a?  Did you try changing to %la (you may
> have already answered that).
>
> Try this test program:
>
> #include <stdio.h>
> int main(void) {
>     char buf[256];
>     double in  = 1.0123456789;
>     double out = 1.0123456789;

Sorry, I should have left `out` uninitialized, or initialized it
to some other value (it was a copy-and-paste error).

>         int result;
>
>         sprintf(buf, "%a", in);
>         result = sscanf(buf, "%la", &out);
>
>         printf("in  = %.10f = %a\n", in, in);
>         printf("buf = \"%s\"\n", buf);
>         printf("sscanf returned %d\n", result);
>         printf("out = %.10f = %a\n", out, out);
>
>         if (in == out) {
>                 puts("in == out");
>         }
>         else {
>                 puts("in != out");
>         }
>         return 0;
> }
[...]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"