in reply to Re: Different behaviour of 'stat' function after assignment to $! (errno).
in thread Different behaviour of 'stat' function after assignment to $! (errno).
It's a little deeper than that.
now yieldsuse Devel::Peek; $! = 0.0; Dump($!); stat("non_existing_file"); Dump($!); die "died at first stat" if -$!; stat("non_existing_file"); Dump($!); die "died at second stat" if -$!;
pNOK is now set, but the value hasn't been updated by stat itself. It's only when $! is referenced that the updated value materializes. I certainly wouldn't recommend using -$!, but perlvar saysSV = PVMG(0x82c690) at 0x803478 REFCNT = 1 FLAGS = (GMG,SMG,pIOK,pNOK) IV = 0 NV = 0 PV = 0 MAGIC = 0x804900 MG_VIRTUAL = &PL_vtbl_sv MG_TYPE = PERL_MAGIC_sv(\0) MG_OBJ = 0x803460 MG_LEN = 1 MG_PTR = 0x8032d0 "!" SV = PVMG(0x82c690) at 0x803478 REFCNT = 1 FLAGS = (GMG,SMG,pIOK,pNOK) IV = 0 NV = 0 PV = 0 MAGIC = 0x804900 MG_VIRTUAL = &PL_vtbl_sv MG_TYPE = PERL_MAGIC_sv(\0) MG_OBJ = 0x803460 MG_LEN = 1 MG_PTR = 0x8032d0 "!" died at first stat at bug.pl line 6.
If used numerically, yields the current value of the C "errno" variable, or in other words, if a system or library call fails, it sets this variable. This means that the value of $! is meaningful only immediately after a failure:so one can be excused for doing numerical things. It also says
You can assign a number to $! to set errno if, for instance, you want "$!" to return the string for error n, or you want to set the exit value for the die() operator.and having to assign a non-integer value to avoid surprises doesn't fall in my category of "do what I mean".
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Re^3: Different behaviour of 'stat' function after assignment to $! (errno).
by ikegami (Patriarch) on May 24, 2011 at 15:56 UTC | |
Re^3: Different behaviour of 'stat' function after assignment to $! (errno).
by Anonymous Monk on May 24, 2011 at 13:31 UTC |
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