Converting a string to a real numeric value

isync has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Converting a string to a real numeric value - what's faster? by mwah (Hermit) on Sep 17, 2009 at 09:18 UTC
First, whats meant by: I ran into an issue that involved quite low-level transformations and as it turned out To your comparison: The code sequence () `$string='7'; $num=$string+0` [download] gives (): `C:\>perl -MO=Concise,-exec -e"$string='7';$num=$string+0" 1 <0> enter 2 <;> nextstate(main 1 -e:1) v:{ 3 <$> const[PV "7"] s 4 <#> gvsv[string] s 5 <2> sassign vKS/2 6 <;> nextstate(main 1 -e:1) v:{ 7 <#> gvsv[string] s 8 <$> const[IV 0] s 9 <2> add[t4] sK/2 a <#> gvsv[num] s b <2> sassign vKS/2 c <@> leave[1 ref] vKP/REFC` [download] and the sequence () `$string='7'; $num=int($string)"` [download] gives () `C:\>perl -MO=Concise,-exec -e"$string='7';$num=int($string)" 1 <0> enter 2 <;> nextstate(main 1 -e:1) v:{ 3 <$> const[PV "7"] s 4 <#> gvsv[string] s 5 <2> sassign vKS/2 6 <;> nextstate(main 1 -e:1) v:{ 7 <#> gvsv[string] s 8 <1> int[t4] sK/1 9 <#> gvsv[num] s a <2> sassign vKS/2 b <@> leave[1 ref] vKP/REFC -e syntax OK` [download] The Difference is () `8 <$> const[IV 0] s 9 <2> add[t4] sK/2` [download] compared to (*) `8 <1> int[t4] sK/1` [download] so there shouldn't be too much difference Regards mwa	[reply] [d/l] [select]
Re^2: Converting a string to a real numeric value - what's faster? by isync (Hermit) on Sep 17, 2009 at 09:50 UTC
Thanks! What I learn from that is: if i am handling non-floating-point values, it's a bit more elegant and possibly a tick faster (one iteration less, 1-b vs 1-c) to use int(), otherwise the +0 trick isn't that much of a hack it seems to be.	[reply]
Re^3: Converting a string to a real numeric value - what's faster? by mwah (Hermit) on Sep 17, 2009 at 10:04 UTC
if i am handling non-floating-point values, it's a bit more elegant ... to use int() .. if it's worth the typed characters at all ;-) As you said before, Perl will convert the string into a number internally if the string isn't already converted (IV-Flag not set) and if the string is used in a numerical context. Of course, when using Perl-Guts (XS), you have to worry. regards mwa	[reply]
Re: Converting a string to a real numeric value - what's faster? by JavaFan (Canon) on Sep 17, 2009 at 09:08 UTC
Now, yesterday, I ran into an issue that involved quite low-level transformations and as it turned out (thanks tofjw!), my string value was simply ignored and a true* numeric value worked.* Really? If that's true, then there's a bug in Perl. Perhaps you can show a code fragment that shows this behaviour? Now: what is the best way to transform a string to a true numeric value, in terms of speed/internal efficiency? You tell us. Run a benchmark and tell us. Note also that they aren't equivalent if $string contains, say "1.23". Of course, I would expect that the fastest solution is to do nothing, and to let perl decide if and when a conversion is needed. And way faster still would be the get rid of Perl, ditch the CGI interface, and write embedded C.	[reply]
Re^2: Converting a string to a real numeric value - what's faster? by isync (Hermit) on Sep 17, 2009 at 09:45 UTC
"Really? If that's true, then there's a bug in Perl." No need to worry: it was a known bug in an XS module I use here, and the developer of the module already fixed it - but it steered my attention towards this string/number thing. "You tell us." Call me a lazy bum, but being the noob that I am at proper benchmarking, I thought a quick post and a question to people who know the Perl internals would be faster.	[reply]
Re^3: Converting a string to a real numeric value - what's faster? by Anonymous Monk on Sep 17, 2009 at 10:04 UTC
to people who know the Perl internals perlmonks ne perl5-porters ;)	[reply]