in reply to sprintf values

Mixing integers and floating point is always problematic, the following illustrates:
use strict; 
use warnings; 

my @num = (3.95,4.95,5.95,8.95,8.94,8.96,9.95,9.96,9.97,9.94,10.08);

foreach (@num){
    my $num = $_ *100;   
    printf ("%d\t%010d\t%011.4f\n", $num, $num, $num);
}

395     0000000395      000395.0000
495     0000000495      000495.0000
595     0000000595      000595.0000
894     0000000894      000895.0000
894     0000000894      000894.0000
896     0000000896      000896.0000
994     0000000994      000995.0000
996     0000000996      000996.0000
997     0000000997      000997.0000
994     0000000994      000994.0000
1008    0000001008      001008.0000

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Update: I just noticed I got slightly different results to you, which only goes to show how untrustworthy conversions are. I am probably running on different hardware, operating system, perl version, and C runtime library to you.

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Re^2: sprintf values
by almut (Canon) on Apr 07, 2010 at 15:41 UTC
    ...and C runtime library

    FWIW, the C runtime library shouldn't matter here, as Perl has its own "printf"-like formatting routine ( Perl_sv_vcatpvfn() in sv.c, in case you're interested ).

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      I think sv_vcatpvfn can or does use the C runtime to format floats. Even if it doesn't, the C runtime is used to create the floats in the first place, so it definitely matters.
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        I just re-checked with ltrace, and yes you're right, it does in fact call snprintf() and frexp() to format floats.

        I had done a similar check some time ago, and was surprised to not find any libc calls related to Perl's s/printf()  (which is why I posted) — but that must have been without a float format specifier being used... (rather only integer formatting like %d, %u etc.)   As to the creation of floats, however, I don't see any calls to libc or libm. Any idea what function that would be (just out of curiosity)?

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