Re: Distinguishing a v-string from something else

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Re: Re: Distinguishing a v-string from something else by John M. Dlugosz (Monsignor) on Dec 05, 2002 at 04:34 UTC
Good point. My context is that of a version number. Adding trailing zeros will not affect the ordering of greater/less, but will affect exact matches using eq (I figured stripping trailing zeros to normalize before comparing for equality). A function that takes an IP address as a buffer of 4 bytes, a v-string (which will UTF-8-encode the values above 127), or a string can tell the difference by looking for the presence of only digits and dots and of the total length. —John	[reply]
Re^3: Distinguishing a v-string from something else by particle (Vicar) on Dec 05, 2002 at 14:44 UTC
a v-string (which will UTF-8-encode the values above 127) actually, they're UTF-8 encoded if they're above 255. `> perl -MDevel::Peek -e"$a=v256;$b=v128;Dump$a;Dump$b" SV = PV(0x182ebf4) at 0x182383c REFCNT = 1 FLAGS = (POK,pPOK,UTF8) PV = 0x182013c "\304\200"\0 CUR = 2 LEN = 3 SV = PV(0x182ec24) at 0x1823848 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x182012c "\200"\0 CUR = 1 LEN = 2` [download] you can differentiate between a number and a v-string by examining the result of the SvPOKp(SV) macro. a true return means a v-string, false indicates a number. if you can differentiate between a v-string and any other string by your above method, you should be able to determine whether or not you have a v-string, no? ~Particle accelerates*	[reply] [d/l] [select]
Re: Re^3: Distinguishing a v-string from something else by John M. Dlugosz (Monsignor) on Dec 10, 2002 at 05:58 UTC
Re: actually, they're UTF-8 encoded if they're above 255. I just got around to verifying this. Actually, it does not work the same as `chr`, in that the v-string encoding faithfully follows the utf8 pragma, while chr decides for itself whether to return a byte or char oriented string regardless of the pragma setting. I'm wondering, though, if a number without a v and only 1 dot (normally a floating-point numeric constant) is dual-valued magic when parsed as the indirect object of a `use` or `require`? Have to peek at what comes into `VERSION`. if you can differentiate between a v-string and any other string by your above method, you should be able to determine whether or not you have a v-string, no? I can easily enough decide if I have a v-string or a string of the form "1.2.3.4" as ASCII, provided it has at least one dot in the latter. That's my purpose: to allow either as the value of $VERSION. —John	[reply] [d/l] [select]
Re^5: Distinguishing a v-string from something else by particle (Vicar) on Dec 10, 2002 at 11:53 UTC
Re^2: Distinguishing a v-string from something else by particle (Vicar) on Dec 05, 2002 at 14:36 UTC
For example, if you get '1.0', that could have really been written '1.0', or 49.46.48. There's no way to tell, other then context. i'm not so sure this is correct. the code below seems to illustrate the storage of v-strings is different than other text strings, as v-strings are stored as octals and periods are not included. \1 is not the same as chr(49). `> perl -MDevel::Peek -e"$a=v1.0; $b='1.0'; Dump$a; Dump$b" SV = PV(0x182ebf4) at 0x182383c REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x182013c "\1\0"\0 CUR = 2 LEN = 3 SV = PV(0x182ec24) at 0x1823848 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x182012c "1.0"\0 CUR = 3 LEN = 4` [download] ~Particle accelerates	[reply] [d/l] [select]
Re: Re^2: Distinguishing a v-string from something else by theorbtwo (Prior) on Dec 06, 2002 at 06:45 UTC
Ahh, but I didn't say that v1.0 eq "1.0"; I said '1.0' eq 49.46.48, and they are: `>perl -MDevel::Peek=Dump -e "$a=49.46.48; $b='1.0'; Dump $a; Dump $b" SV = PV(0x225484) at 0x19245fc REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x22ce4c "1.0"\0 CUR = 3 LEN = 4 SV = PV(0x2254b4) at 0x1924608 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x22b424 "1.0"\0 CUR = 3 LEN = 4` [download] Oh, two BTWs: all strings are stored as an array of chars (c-style); base doesn't enter into it, in the same way as 0x10 and 16 are both the same number. It's just that Devel::Peek prints nonprintable characters as octal escapes. Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).	[reply] [d/l]