Re: Different behaviour of 'stat' function after assignment to $! (errno).

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Re^2: Different behaviour of 'stat' function after assignment to $! (errno). by jpl (Monk) on May 24, 2011 at 11:27 UTC
I can reproduce it, but not explain it. `use Devel::Peek; $! = 0; Dump($!); stat("non_existing_file"); Dump($!); die "died at first stat" if -$!; stat("non_existing_file"); Dump($!); die "died at second stat" if -$!;` [download] yields SV = PVMG(0x214d690) at 0x2124478 REFCNT = 1 FLAGS = (GMG,SMG,pIOK) IV = 0 NV = 0 PV = 0 MAGIC = 0x2125900 MG_VIRTUAL = &PL_vtbl_sv MG_TYPE = PERL_MAGIC_sv(\0) MG_OBJ = 0x2124460 MG_LEN = 1 MG_PTR = 0x21242d0 "!" SV = PVMG(0x214d690) at 0x2124478 REFCNT = 1 FLAGS = (GMG,SMG,pIOK) IV = 0 NV = 0 PV = 0 MAGIC = 0x2125900 MG_VIRTUAL = &PL_vtbl_sv MG_TYPE = PERL_MAGIC_sv(\0) MG_OBJ = 0x2124460 MG_LEN = 1 MG_PTR = 0x21242d0 "!" SV = PVMG(0x214d690) at 0x2124478 REFCNT = 1 FLAGS = (GMG,SMG,pNOK,pPOK) IV = 0 NV = 2 PV = 0x21243a0 "No such file or directory"\0 CUR = 25 LEN = 32 MAGIC = 0x2125900 MG_VIRTUAL = &PL_vtbl_sv MG_TYPE = PERL_MAGIC_sv(\0) MG_OBJ = 0x2124460 MG_LEN = 1 MG_PTR = 0x21242d0 "!" died at second stat at bug.pl line 9. [download] Nothing "funny" has been done to $! before the second Dump, but it hasn't changed since before the stat.	[reply] [d/l] [select]
Re^3: Different behaviour of 'stat' function after assignment to $! (errno). by Anonymous Monk on May 24, 2011 at 11:45 UTC
Nothing "funny" has been done to $! before the second Dump, but it hasn't changed since before the stat. $! , errno, is supposed to be positive, so using -$! is something funny :)	[reply]
Re^4: Different behaviour of 'stat' function after assignment to $! (errno). by ikegami (Patriarch) on May 24, 2011 at 15:53 UTC
Negating positive numbers isn't doing something funny.	[reply]
Re^4: Different behaviour of 'stat' function after assignment to $! (errno). by jpl (Monk) on May 24, 2011 at 12:29 UTC
$! , errno, is supposed to be positive, so using -$! is something funny :) All the "funny" stuff happens after the second Dump, which happens immediately after the stat. Unless the optimizer is punishing us for something that is going to happen later, I cannot explain why the failing stat did not appear to modify $!.	[reply]
Re^5: Different behaviour of 'stat' function after assignment to $! (errno). by Anonymous Monk on May 24, 2011 at 12:54 UTC
Re^3: Different behaviour of 'stat' function after assignment to $! (errno). by Anonymous Monk on May 24, 2011 at 11:54 UTC
The battle of IV versus NV, lol $ perl -MDevel::Peek -e " Dump($!); $!=20; stat 1; printf qq[%d %s %d\ +n], $!,$!,-$!; Dump($!); " SV = PVMG(0x9b3adc) at 0x9ba5ac REFCNT = 1 FLAGS = (GMG,SMG) IV = 0 NV = 0 PV = 0 MAGIC = 0x9c6d9c MG_VIRTUAL = &PL_vtbl_sv MG_TYPE = PERL_MAGIC_sv(\0) MG_OBJ = 0x9ba59c MG_LEN = 1 MG_PTR = 0x9c2b7c "!" 2 No such file or directory -20 SV = PVMG(0x9b3adc) at 0x9ba5ac REFCNT = 1 FLAGS = (GMG,SMG,pNOK,pPOK) IV = 20 NV = 2 PV = 0x3ffed4 "No such file or directory"\0 CUR = 25 LEN = 28 MAGIC = 0x9c6d9c MG_VIRTUAL = &PL_vtbl_sv MG_TYPE = PERL_MAGIC_sv(\0) MG_OBJ = 0x9ba59c MG_LEN = 1 MG_PTR = 0x9c2b7c "!" [download]	[reply] [d/l]