devel::peek.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

\&          FLAGS = (IOK,pIOK)
\&          IV = 42
.Ve
.PP
This says \f(CW$a\fR is an \s-1SV\s0, a scalar.  The scalar is an \s-1IV\s0, a number.  Its
reference count is 1.  It has the \f(CW\*(C`IOK\*(C'\fR flag set, meaning it is currently
being evaluated as a number.  Because \s-1IOK\s0 is set we look at the \s-1IV\s0 item to
see what is in the scalar.
.Sh "A simple scalar with an extra reference"
.IX Subsection "A simple scalar with an extra reference"
If the scalar from the previous example had an extra reference:
.PP
.Vb 4
\&        use Devel::Peek;
\&        $a = 42;
\&        $b = \e$a;
\&        Dump $a;
.Ve
.PP
The output:
.PP
.Vb 4
\&        SV = IV(0xbe860)
\&          REFCNT = 2
\&          FLAGS = (IOK,pIOK)
\&          IV = 42
.Ve
.PP
Notice that this example differs from the previous example only in its
reference count.  Compare this to the next example, where we dump \f(CW$b\fR
instead of \f(CW$a\fR.
.Sh "A reference to a simple scalar"
.IX Subsection "A reference to a simple scalar"
This shows what a reference looks like when it references a simple scalar.
.PP
.Vb 4
\&        use Devel::Peek;
\&        $a = 42;
\&        $b = \e$a;
\&        Dump $b;
.Ve
.PP
The output:
.PP
.Vb 8
\&        SV = RV(0xf041c)
\&          REFCNT = 1
\&          FLAGS = (ROK)
\&          RV = 0xbab08
\&        SV = IV(0xbe860)
\&          REFCNT = 2
\&          FLAGS = (IOK,pIOK)
\&          IV = 42
.Ve
.PP
Starting from the top, this says \f(CW$b\fR is an \s-1SV\s0.  The scalar is an \s-1RV\s0, a
reference.  It has the \f(CW\*(C`ROK\*(C'\fR flag set, meaning it is a reference.  Because
\&\s-1ROK\s0 is set we have an \s-1RV\s0 item rather than an \s-1IV\s0 or \s-1PV\s0.  Notice that Dump
follows the reference and shows us what \f(CW$b\fR was referencing.  We see the
same \f(CW$a\fR that we found in the previous example.
.PP
Note that the value of \f(CW\*(C`RV\*(C'\fR coincides with the numbers we see when we
stringify \f(CW$b\fR. The addresses inside \s-1\fIRV\s0()\fR and \s-1\fIIV\s0()\fR are addresses of
\&\f(CW\*(C`X***\*(C'\fR structure which holds the current state of an \f(CW\*(C`SV\*(C'\fR. This
address may change during lifetime of an \s-1SV\s0.
.Sh "A reference to an array"
.IX Subsection "A reference to an array"
This shows what a reference to an array looks like.
.PP
.Vb 3
\&        use Devel::Peek;
\&        $a = [42];
\&        Dump $a;
.Ve
.PP
The output:
.PP
.Vb 10
\&        SV = RV(0xf041c)
\&          REFCNT = 1
\&          FLAGS = (ROK)
\&          RV = 0xb2850
\&        SV = PVAV(0xbd448)
\&          REFCNT = 1
\&          FLAGS = ()
\&          IV = 0
\&          NV = 0
\&          ARRAY = 0xb2048
\&          ALLOC = 0xb2048
\&          FILL = 0
\&          MAX = 0
\&          ARYLEN = 0x0
\&          FLAGS = (REAL)
\&        Elt No. 0 0xb5658
\&        SV = IV(0xbe860)
\&          REFCNT = 1
\&          FLAGS = (IOK,pIOK)
\&          IV = 42
.Ve
.PP
This says \f(CW$a\fR is an \s-1SV\s0 and that it is an \s-1RV\s0.  That \s-1RV\s0 points to
another \s-1SV\s0 which is a \s-1PVAV\s0, an array.  The array has one element,
element zero, which is another \s-1SV\s0. The field \f(CW\*(C`FILL\*(C'\fR above indicates
the last element in the array, similar to \f(CW\*(C`$#$a\*(C'\fR.
.PP
If \f(CW$a\fR pointed to an array of two elements then we would see the
following.
.PP
.Vb 3
\&        use Devel::Peek \*(AqDump\*(Aq;
\&        $a = [42,24];
\&        Dump $a;
.Ve
.PP
The output:
.PP
.Vb 10
\&        SV = RV(0xf041c)
\&          REFCNT = 1
\&          FLAGS = (ROK)
\&          RV = 0xb2850
\&        SV = PVAV(0xbd448)
\&          REFCNT = 1
\&          FLAGS = ()
\&          IV = 0
\&          NV = 0
\&          ARRAY = 0xb2048
\&          ALLOC = 0xb2048
\&          FILL = 0
\&          MAX = 0
\&          ARYLEN = 0x0
\&          FLAGS = (REAL)
\&        Elt No. 0  0xb5658
\&        SV = IV(0xbe860)
\&          REFCNT = 1
\&          FLAGS = (IOK,pIOK)
\&          IV = 42
\&        Elt No. 1  0xb5680
\&        SV = IV(0xbe818)
\&          REFCNT = 1
\&          FLAGS = (IOK,pIOK)
\&          IV = 24
.Ve
.PP
Note that \f(CW\*(C`Dump\*(C'\fR will not report \fIall\fR the elements in the array,
only several first (depending on how deep it already went into the
report tree).
.Sh "A reference to a hash"
.IX Subsection "A reference to a hash"
The following shows the raw form of a reference to a hash.
.PP
.Vb 3
\&        use Devel::Peek;
\&        $a = {hello=>42};
\&        Dump $a;
.Ve
.PP
The output:
.PP
.Vb 10
\&        SV = RV(0x8177858) at 0x816a618
\&          REFCNT = 1
\&          FLAGS = (ROK)
\&          RV = 0x814fc10
\&          SV = PVHV(0x8167768) at 0x814fc10
\&            REFCNT = 1
\&            FLAGS = (SHAREKEYS)
\&            IV = 1
\&            NV = 0
\&            ARRAY = 0x816c5b8  (0:7, 1:1)
\&            hash quality = 100.0%
\&            KEYS = 1
\&            FILL = 1
\&            MAX = 7
\&            RITER = \-1
\&            EITER = 0x0
\&            Elt "hello" HASH = 0xc8fd181b
\&            SV = IV(0x816c030) at 0x814fcf4
\&              REFCNT = 1
\&              FLAGS = (IOK,pIOK)
\&              IV = 42
.Ve
.PP
This shows \f(CW$a\fR is a reference pointing to an \s-1SV\s0.  That \s-1SV\s0 is a \s-1PVHV\s0, a
hash. Fields \s-1RITER\s0 and \s-1EITER\s0 are used by \f(CW\*(C`each\*(C'\fR.
.PP
The \*(L"quality\*(R" of a hash is defined as the total number of comparisons needed
to access every element once, relative to the expected number needed for a
random hash. The value can go over 100%.
.PP
The total number of comparisons is equal to the sum of the squares of the
number of entries in each bucket.  For a random hash of \f(CW\*(C`<n\*(C'\fR> keys into
\&\f(CW\*(C`<k\*(C'\fR> buckets, the expected value is:
.PP
.Vb 1
\&                n + n(n\-1)/2k
.Ve
.Sh "Dumping a large array or hash"
.IX Subsection "Dumping a large array or hash"
The \f(CW\*(C`Dump()\*(C'\fR function, by default, dumps up to 4 elements from a
toplevel array or hash.  This number can be increased by supplying a
second argument to the function.
.PP
.Vb 3
\&        use Devel::Peek;
\&        $a = [10,11,12,13,14];
\&        Dump $a;
.Ve
.PP
Notice that \f(CW\*(C`Dump()\*(C'\fR prints only elements 10 through 13 in the above code.
The following code will print all of the elements.
.PP
.Vb 3
\&        use Devel::Peek \*(AqDump\*(Aq;
\&        $a = [10,11,12,13,14];
\&        Dump $a, 5;
.Ve
.Sh "A reference to an \s-1SV\s0 which holds a C pointer"
.IX Subsection "A reference to an SV which holds a C pointer"
This is what you really need to know as an \s-1XS\s0 programmer, of course.  When
an \s-1XSUB\s0 returns a pointer to a C structure that pointer is stored in an \s-1SV\s0
and a reference to that \s-1SV\s0 is placed on the \s-1XSUB\s0 stack.  So the output from
an \s-1XSUB\s0 which uses something like the T_PTROBJ map might look something like
this:
.PP
.Vb 11
\&        SV = RV(0xf381c)
\&          REFCNT = 1
\&          FLAGS = (ROK)
\&          RV = 0xb8ad8
\&        SV = PVMG(0xbb3c8)
\&          REFCNT = 1
\&          FLAGS = (OBJECT,IOK,pIOK)
\&          IV = 729160
\&          NV = 0
\&          PV = 0
\&          STASH = 0xc1d10       "CookBookB::Opaque"
.Ve
.PP
This shows that we have an \s-1SV\s0 which is an \s-1RV\s0.  That \s-1RV\s0 points at another
\&\s-1SV\s0.  In this case that second \s-1SV\s0 is a \s-1PVMG\s0, a blessed scalar.  Because it is
blessed it has the \f(CW\*(C`OBJECT\*(C'\fR flag set.  Note that an \s-1SV\s0 which holds a C
pointer also has the \f(CW\*(C`IOK\*(C'\fR flag set.  The \f(CW\*(C`STASH\*(C'\fR is set to the package
name which this \s-1SV\s0 was blessed into.
.PP
The output from an \s-1XSUB\s0 which uses something like the T_PTRREF map, which
doesn't bless the object, might look something like this:
.PP
.Vb 10
\&        SV = RV(0xf381c)
\&          REFCNT = 1
\&          FLAGS = (ROK)
\&          RV = 0xb8ad8
\&        SV = PVMG(0xbb3c8)
\&          REFCNT = 1
\&          FLAGS = (IOK,pIOK)
\&          IV = 729160
\&          NV = 0
\&          PV = 0
.Ve
.Sh "A reference to a subroutine"
.IX Subsection "A reference to a subroutine"
Looks like this:
.PP
.Vb 10
\&        SV = RV(0x798ec)
\&          REFCNT = 1
\&          FLAGS = (TEMP,ROK)
\&          RV = 0x1d453c
\&        SV = PVCV(0x1c768c)
\&          REFCNT = 2
\&          FLAGS = ()
\&          IV = 0
\&          NV = 0
\&          COMP_STASH = 0x31068  "main"
\&          START = 0xb20e0
\&          ROOT = 0xbece0
\&          XSUB = 0x0
\&          XSUBANY = 0
\&          GVGV::GV = 0x1d44e8   "MY" :: "top_targets"
\&          FILE = "(eval 5)"
\&          DEPTH = 0
\&          PADLIST = 0x1c9338
.Ve
.PP
This shows that
.IP "\(bu" 4
the subroutine is not an \s-1XSUB\s0 (since \f(CW\*(C`START\*(C'\fR and \f(CW\*(C`ROOT\*(C'\fR are
non-zero, and \f(CW\*(C`XSUB\*(C'\fR is zero);
.IP "\(bu" 4
that it was compiled in the package \f(CW\*(C`main\*(C'\fR;
.IP "\(bu" 4
under the name \f(CW\*(C`MY::top_targets\*(C'\fR;
.IP "\(bu" 4
inside a 5th eval in the program;
.IP "\(bu" 4
it is not currently executed (see \f(CW\*(C`DEPTH\*(C'\fR);
.IP "\(bu" 4
it has no prototype (\f(CW\*(C`PROTOTYPE\*(C'\fR field is missing).
.SH "EXPORTS"
.IX Header "EXPORTS"
\&\f(CW\*(C`Dump\*(C'\fR, \f(CW\*(C`mstat\*(C'\fR, \f(CW\*(C`DeadCode\*(C'\fR, \f(CW\*(C`DumpArray\*(C'\fR, \f(CW\*(C`DumpWithOP\*(C'\fR and
\&\f(CW\*(C`DumpProg\*(C'\fR, \f(CW\*(C`fill_mstats\*(C'\fR, \f(CW\*(C`mstats_fillhash\*(C'\fR, \f(CW\*(C`mstats2hash\*(C'\fR by
default. Additionally available \f(CW\*(C`SvREFCNT\*(C'\fR, \f(CW\*(C`SvREFCNT_inc\*(C'\fR and
\&\f(CW\*(C`SvREFCNT_dec\*(C'\fR.
.SH "BUGS"
.IX Header "BUGS"
Readers have been known to skip important parts of perlguts, causing much
frustration for all.
.SH "AUTHOR"
.IX Header "AUTHOR"
Ilya Zakharevich	[e-mail]\-state.edu
.PP
Copyright (c) 1995\-98 Ilya Zakharevich. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
.PP
Author of this software makes no claim whatsoever about suitability,
reliability, edability, editability or usability of this product, and
should not be kept liable for any damage resulting from the use of
it. If you can use it, you are in luck, if not, I should not be kept
responsible. Keep a handy copy of your backup tape at hand.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
perlguts, and perlguts, again.