perlapio.1

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.

to have \*(L"file\*(R" first.  Arranges that next read operation will return
the byte \fBc\fR.  Despite the implied \*(L"character\*(R" in the name only
values in the range 0..0xFF are defined. Returns the byte \fBc\fR on
success or \-1 (\f(CW\*(C`EOF\*(C'\fR) on error.  The number of bytes that can be
\&\*(L"pushed back\*(R" may vary, only 1 character is certain, and then only if
it is the last character that was read from the handle.
.IP "\fBPerlIO_getc(f)\fR" 4
.IX Item "PerlIO_getc(f)"
This corresponds to \fIgetc()\fR.
Despite the c in the name only byte range 0..0xFF is supported.
Returns the character read or \-1 (\f(CW\*(C`EOF\*(C'\fR) on error.
.IP "\fBPerlIO_eof(f)\fR" 4
.IX Item "PerlIO_eof(f)"
This corresponds to \fIfeof()\fR.  Returns a true/false indication of
whether the handle is at end of file.  For terminal devices this may
or may not be \*(L"sticky\*(R" depending on the implementation.  The flag is
cleared by \fIPerlIO_seek()\fR, or \fIPerlIO_rewind()\fR.
.IP "\fBPerlIO_error(f)\fR" 4
.IX Item "PerlIO_error(f)"
This corresponds to \fIferror()\fR.  Returns a true/false indication of
whether there has been an \s-1IO\s0 error on the handle.
.IP "\fBPerlIO_fileno(f)\fR" 4
.IX Item "PerlIO_fileno(f)"
This corresponds to \fIfileno()\fR, note that on some platforms, the meaning
of \*(L"fileno\*(R" may not match Unix. Returns \-1 if the handle has no open
descriptor associated with it.
.IP "\fBPerlIO_clearerr(f)\fR" 4
.IX Item "PerlIO_clearerr(f)"
This corresponds to \fIclearerr()\fR, i.e., clears 'error' and (usually)
\&'eof' flags for the \*(L"stream\*(R". Does not return a value.
.IP "\fBPerlIO_flush(f)\fR" 4
.IX Item "PerlIO_flush(f)"
This corresponds to \fIfflush()\fR.  Sends any buffered write data to the
underlying file.  If called with \f(CW\*(C`NULL\*(C'\fR this may flush all open
streams (or core dump with some \s-1USE_STDIO\s0 implementations).  Calling
on a handle open for read only, or on which last operation was a read
of some kind may lead to undefined behaviour on some \s-1USE_STDIO\s0
implementations.  The \s-1USE_PERLIO\s0 (layers) implementation tries to
behave better: it flushes all open streams when passed \f(CW\*(C`NULL\*(C'\fR, and
attempts to retain data on read streams either in the buffer or by
seeking the handle to the current logical position.
.IP "\fBPerlIO_seek(f,offset,whence)\fR" 4
.IX Item "PerlIO_seek(f,offset,whence)"
This corresponds to \fIfseek()\fR.  Sends buffered write data to the
underlying file, or discards any buffered read data, then positions
the file descriptor as specified by \fBoffset\fR and \fBwhence\fR (sic).
This is the correct thing to do when switching between read and write
on the same handle (see issues with \fIPerlIO_flush()\fR above).  Offset is
of type \f(CW\*(C`Off_t\*(C'\fR which is a perl Configure value which may not be same
as stdio's \f(CW\*(C`off_t\*(C'\fR.
.IP "\fBPerlIO_tell(f)\fR" 4
.IX Item "PerlIO_tell(f)"
This corresponds to \fIftell()\fR.  Returns the current file position, or
(Off_t) \-1 on error.  May just return value system \*(L"knows\*(R" without
making a system call or checking the underlying file descriptor (so
use on shared file descriptors is not safe without a
\&\fIPerlIO_seek()\fR). Return value is of type \f(CW\*(C`Off_t\*(C'\fR which is a perl
Configure value which may not be same as stdio's \f(CW\*(C`off_t\*(C'\fR.
.IP "\fBPerlIO_getpos(f,p)\fR, \fBPerlIO_setpos(f,p)\fR" 4
.IX Item "PerlIO_getpos(f,p), PerlIO_setpos(f,p)"
These correspond (loosely) to \fIfgetpos()\fR and \fIfsetpos()\fR. Rather than
stdio's Fpos_t they expect a \*(L"Perl Scalar Value\*(R" to be passed. What is
stored there should be considered opaque. The layout of the data may
vary from handle to handle.  When not using stdio or if platform does
not have the stdio calls then they are implemented in terms of
\&\fIPerlIO_tell()\fR and \fIPerlIO_seek()\fR.
.IP "\fBPerlIO_rewind(f)\fR" 4
.IX Item "PerlIO_rewind(f)"
This corresponds to \fIrewind()\fR. It is usually defined as being
.Sp
.Vb 2
\&    PerlIO_seek(f,(Off_t)0L, SEEK_SET);
\&    PerlIO_clearerr(f);
.Ve
.IP "\fB\f(BIPerlIO_tmpfile()\fB\fR" 4
.IX Item "PerlIO_tmpfile()"
This corresponds to \fItmpfile()\fR, i.e., returns an anonymous PerlIO or
\&\s-1NULL\s0 on error.  The system will attempt to automatically delete the
file when closed.  On Unix the file is usually \f(CW\*(C`unlink\*(C'\fR\-ed just after
it is created so it does not matter how it gets closed. On other
systems the file may only be deleted if closed via \fIPerlIO_close()\fR
and/or the program exits via \f(CW\*(C`exit\*(C'\fR.  Depending on the implementation
there may be \*(L"race conditions\*(R" which allow other processes access to
the file, though in general it will be safer in this regard than
ad. hoc. schemes.
.IP "\fBPerlIO_setlinebuf(f)\fR" 4
.IX Item "PerlIO_setlinebuf(f)"
This corresponds to \fIsetlinebuf()\fR.  Does not return a value. What
constitutes a \*(L"line\*(R" is implementation dependent but usually means
that writing \*(L"\en\*(R" flushes the buffer.  What happens with things like
\&\*(L"this\enthat\*(R" is uncertain.  (Perl core uses it \fIonly\fR when \*(L"dumping\*(R";
it has nothing to do with $| auto-flush.)
.Sh "Co-existence with stdio"
.IX Subsection "Co-existence with stdio"
There is outline support for co-existence of PerlIO with stdio.
Obviously if PerlIO is implemented in terms of stdio there is no
problem. However in other cases then mechanisms must exist to create a
\&\s-1FILE\s0 * which can be passed to library code which is going to use stdio
calls.
.PP
The first step is to add this line:
.PP
.Vb 1
\&   #define PERLIO_NOT_STDIO 0
.Ve
.PP
\&\fIbefore\fR including any perl header files. (This will probably become
the default at some point).  That prevents \*(L"perlio.h\*(R" from attempting
to #define stdio functions onto PerlIO functions.
.PP
\&\s-1XS\s0 code is probably better using \*(L"typemap\*(R" if it expects \s-1FILE\s0 *
arguments.  The standard typemap will be adjusted to comprehend any
changes in this area.
.IP "\fBPerlIO_importFILE(f,mode)\fR" 4
.IX Item "PerlIO_importFILE(f,mode)"
Used to get a PerlIO * from a \s-1FILE\s0 *.
.Sp
The mode argument should be a string as would be passed to
fopen/PerlIO_open.  If it is \s-1NULL\s0 then \- for legacy support \- the code
will (depending upon the platform and the implementation) either
attempt to empirically determine the mode in which \fIf\fR is open, or
use \*(L"r+\*(R" to indicate a read/write stream.
.Sp
Once called the \s-1FILE\s0 * should \fI\s-1ONLY\s0\fR be closed by calling
\&\f(CW\*(C`PerlIO_close()\*(C'\fR on the returned PerlIO *.
.Sp
The PerlIO is set to textmode. Use PerlIO_binmode if this is
not the desired mode.
.Sp
This is \fBnot\fR the reverse of \fIPerlIO_exportFILE()\fR.
.IP "\fBPerlIO_exportFILE(f,mode)\fR" 4
.IX Item "PerlIO_exportFILE(f,mode)"
Given a PerlIO * create a 'native' \s-1FILE\s0 * suitable for passing to code
expecting to be compiled and linked with \s-1ANSI\s0 C \fIstdio.h\fR.  The mode
argument should be a string as would be passed to fopen/PerlIO_open.
If it is \s-1NULL\s0 then \- for legacy support \- the \s-1FILE\s0 * is opened in same
mode as the PerlIO *.
.Sp
The fact that such a \s-1FILE\s0 * has been 'exported' is recorded, (normally
by pushing a new :stdio \*(L"layer\*(R" onto the PerlIO *), which may affect
future PerlIO operations on the original PerlIO *.  You should not
call \f(CW\*(C`fclose()\*(C'\fR on the file unless you call \f(CW\*(C`PerlIO_releaseFILE()\*(C'\fR
to disassociate it from the PerlIO *.  (Do not use \fIPerlIO_importFILE()\fR
for doing the disassociation.)
.Sp
Calling this function repeatedly will create a \s-1FILE\s0 * on each call
(and will push an :stdio layer each time as well).
.IP "\fBPerlIO_releaseFILE(p,f)\fR" 4
.IX Item "PerlIO_releaseFILE(p,f)"
Calling PerlIO_releaseFILE informs PerlIO that all use of \s-1FILE\s0 * is
complete. It is removed from the list of 'exported' \s-1FILE\s0 *s, and the
associated PerlIO * should revert to its original behaviour.
.Sp
Use this to disassociate a file from a PerlIO * that was associated
using \fIPerlIO_exportFILE()\fR.
.IP "\fBPerlIO_findFILE(f)\fR" 4
.IX Item "PerlIO_findFILE(f)"
Returns a native \s-1FILE\s0 * used by a stdio layer. If there is none, it
will create one with PerlIO_exportFILE. In either case the \s-1FILE\s0 *
should be considered as belonging to PerlIO subsystem and should
only be closed by calling \f(CW\*(C`PerlIO_close()\*(C'\fR.
.ie n .Sh """Fast gets"" Functions"
.el .Sh "``Fast gets'' Functions"
.IX Subsection "Fast gets Functions"
In addition to standard-like \s-1API\s0 defined so far above there is an
\&\*(L"implementation\*(R" interface which allows perl to get at internals of
PerlIO.  The following calls correspond to the various FILE_xxx macros
determined by Configure \- or their equivalent in other
implementations. This section is really of interest to only those
concerned with detailed perl-core behaviour, implementing a PerlIO
mapping or writing code which can make use of the \*(L"read ahead\*(R" that
has been done by the \s-1IO\s0 system in the same way perl does. Note that
any code that uses these interfaces must be prepared to do things the
traditional way if a handle does not support them.
.IP "\fBPerlIO_fast_gets(f)\fR" 4
.IX Item "PerlIO_fast_gets(f)"
Returns true if implementation has all the interfaces required to
allow perl's \f(CW\*(C`sv_gets\*(C'\fR to \*(L"bypass\*(R" normal \s-1IO\s0 mechanism.  This can
vary from handle to handle.
.Sp
.Vb 3
\&  PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \e
\&                        PerlIO_canset_cnt(f) && \e
\&                        \`Can set pointer into buffer\*(Aq
.Ve
.IP "\fBPerlIO_has_cntptr(f)\fR" 4
.IX Item "PerlIO_has_cntptr(f)"
Implementation can return pointer to current position in the \*(L"buffer\*(R"
and a count of bytes available in the buffer.  Do not use this \- use
PerlIO_fast_gets.
.IP "\fBPerlIO_get_cnt(f)\fR" 4
.IX Item "PerlIO_get_cnt(f)"
Return count of readable bytes in the buffer. Zero or negative return
means no more bytes available.
.IP "\fBPerlIO_get_ptr(f)\fR" 4
.IX Item "PerlIO_get_ptr(f)"
Return pointer to next readable byte in buffer, accessing via the
pointer (dereferencing) is only safe if \fIPerlIO_get_cnt()\fR has returned
a positive value.  Only positive offsets up to value returned by
\&\fIPerlIO_get_cnt()\fR are allowed.
.IP "\fBPerlIO_set_ptrcnt(f,p,c)\fR" 4
.IX Item "PerlIO_set_ptrcnt(f,p,c)"
Set pointer into buffer, and a count of bytes still in the
buffer. Should be used only to set pointer to within range implied by
previous calls to \f(CW\*(C`PerlIO_get_ptr\*(C'\fR and \f(CW\*(C`PerlIO_get_cnt\*(C'\fR. The two
values \fImust\fR be consistent with each other (implementation may only
use one or the other or may require both).
.IP "\fBPerlIO_canset_cnt(f)\fR" 4
.IX Item "PerlIO_canset_cnt(f)"
Implementation can adjust its idea of number of bytes in the buffer.
Do not use this \- use PerlIO_fast_gets.
.IP "\fBPerlIO_set_cnt(f,c)\fR" 4
.IX Item "PerlIO_set_cnt(f,c)"
Obscure \- set count of bytes in the buffer. Deprecated.  Only usable
if \fIPerlIO_canset_cnt()\fR returns true.  Currently used in only doio.c to
force count less than \-1 to \-1.  Perhaps should be PerlIO_set_empty or
similar.  This call may actually do nothing if \*(L"count\*(R" is deduced from
pointer and a \*(L"limit\*(R".  Do not use this \- use \fIPerlIO_set_ptrcnt()\fR.
.IP "\fBPerlIO_has_base(f)\fR" 4
.IX Item "PerlIO_has_base(f)"
Returns true if implementation has a buffer, and can return pointer
to whole buffer and its size. Used by perl for \fB\-T\fR / \fB\-B\fR tests.
Other uses would be very obscure...
.IP "\fBPerlIO_get_base(f)\fR" 4
.IX Item "PerlIO_get_base(f)"
Return \fIstart\fR of buffer. Access only positive offsets in the buffer
up to the value returned by \fIPerlIO_get_bufsiz()\fR.
.IP "\fBPerlIO_get_bufsiz(f)\fR" 4
.IX Item "PerlIO_get_bufsiz(f)"
Return the \fItotal number of bytes\fR in the buffer, this is neither the
number that can be read, nor the amount of memory allocated to the
buffer. Rather it is what the operating system and/or implementation
happened to \f(CW\*(C`read()\*(C'\fR (or whatever) last time \s-1IO\s0 was requested.
.Sh "Other Functions"
.IX Subsection "Other Functions"
.IP "PerlIO_apply_layers(f,mode,layers)" 4
.IX Item "PerlIO_apply_layers(f,mode,layers)"
The new interface to the \s-1USE_PERLIO\s0 implementation. The layers \*(L":crlf\*(R"
and \*(L":raw\*(R" are only ones allowed for other implementations and those
are silently ignored. (As of perl5.8 \*(L":raw\*(R" is deprecated.)  Use
\&\fIPerlIO_binmode()\fR below for the portable case.
.IP "PerlIO_binmode(f,ptype,imode,layers)" 4
.IX Item "PerlIO_binmode(f,ptype,imode,layers)"
The hook used by perl's \f(CW\*(C`binmode\*(C'\fR operator.
\&\fBptype\fR is perl's character for the kind of \s-1IO:\s0
.RS 4
.IP "'<' read" 8
.IX Item "'<' read"
.PD 0
.IP "'>' write" 8
.IX Item "'>' write"
.IP "'+' read/write" 8
.IX Item "'+' read/write"
.RE
.RS 4
.PD
.Sp
\&\fBimode\fR is \f(CW\*(C`O_BINARY\*(C'\fR or \f(CW\*(C`O_TEXT\*(C'\fR.
.Sp
\&\fBlayers\fR is a string of layers to apply, only \*(L":crlf\*(R" makes sense in
the non \s-1USE_PERLIO\s0 case. (As of perl5.8 \*(L":raw\*(R" is deprecated in favour
of passing \s-1NULL\s0.)
.Sp
Portable cases are:
.Sp
.Vb 3
\&    PerlIO_binmode(f,ptype,O_BINARY,Nullch);
\&and
\&    PerlIO_binmode(f,ptype,O_TEXT,":crlf");
.Ve
.Sp
On Unix these calls probably have no effect whatsoever.  Elsewhere
they alter \*(L"\en\*(R" to \s-1CR\s0,LF translation and possibly cause a special text
\&\*(L"end of file\*(R" indicator to be written or honoured on read. The effect
of making the call after doing any \s-1IO\s0 to the handle depends on the
implementation. (It may be ignored, affect any data which is already
buffered as well, or only apply to subsequent data.)
.RE
.IP "PerlIO_debug(fmt,...)" 4
.IX Item "PerlIO_debug(fmt,...)"
PerlIO_debug is a \fIprintf()\fR\-like function which can be used for
debugging.  No return value. Its main use is inside PerlIO where using
real printf, \fIwarn()\fR etc. would recursively call PerlIO and be a
problem.
.Sp
PerlIO_debug writes to the file named by \f(CW$ENV\fR{'\s-1PERLIO_DEBUG\s0'} typical
use might be
.Sp
.Vb 2
\&  Bourne shells (sh, ksh, bash, zsh, ash, ...):
\&   PERLIO_DEBUG=/dev/tty ./perl somescript some args
\&
\&  Csh/Tcsh:
\&   setenv PERLIO_DEBUG /dev/tty
\&   ./perl somescript some args
\&
\&  If you have the "env" utility:
\&   env PERLIO_DEBUG=/dev/tty ./perl somescript some args
\&
\&  Win32:
\&   set PERLIO_DEBUG=CON
\&   perl somescript some args
.Ve
.Sp
If \f(CW$ENV\fR{'\s-1PERLIO_DEBUG\s0'} is not set \fIPerlIO_debug()\fR is a no-op.