docs/latex/wx/tstream.tex

   1 \section{Streams in wxWindows overview}\label{wxstreamoverview}
   2
   3 Classes: \helpref{wxStreamBase}{wxstreambase},
   4  \helpref{wxStreamBuffer}{wxstreambuffer}, \helpref{wxInputStream}{wxinputstream},
   5  \helpref{wxOutputStream}{wxoutputstream},
   6  \helpref{wxFilterInputStream}{wxfilterinputstream},
   7  \helpref{wxFilterOutputStream}{wxfilteroutputstream}
   8
   9 \wxheading{Purpose of wxStream}
  10
  11 We went into troubles with c++ std streams on some platform:
  12 they react quite well in most cases, but in multi-threaded case, for example,
  13 they have a LOT of problems.
  14
  15 Then, wxStreams have been built in wxWindows because an application should compile
  16 and run on all supported platforms and we don't want users depend on release
  17 X.XX of libg++ or some other compiler to run the program.
  18
  19 wxStreams is divided in two main parts:
  20 \begin{enumerate}\itemsep=0pt
  21 \item the core: wxStreamBase, wxStreamBuffer, wxInputStream, wxOutputStream,
  22 wxFilterIn/OutputStream
  23 \item the "IO" classes: wxSocketIn/OutputStream, wxDataIn/OutputStream, wxFileIn/OutputStream, ...
  24 \end{enumerate}
  25
  26 wxStreamBase is the base definition of a stream. It defines, for example,
  27 the API of OnSysRead, OnSysWrite, OnSysSeek and OnSysTell. These functions are
  28 are really implemented by the "IO" classes.
  29 wxInputStream and wxOutputStream inherit from it.
  30
  31 wxStreamBuffer is a cache manager for wxStreamBase (it manages a stream buffer
  32 linked to a stream). One stream can have multiple stream buffers  but one stream
  33 have always one autoinitialized stream buffer.
  34
  35 wxInputStream is the base class for read-only streams. It implements Read,
  36 SeekI (I for Input), and all read or IO generic related functions.
  37 wxOutputStream does the same thing but it is for write-only streams.
  38
  39 wxFilterIn/OutputStream is base class definition for stream filtering.
  40 I mean by stream filtering, a stream which does no syscall but filter datas
  41 which are passed to it and then pass them to another stream.
  42 For example, wxZLibInputStream is an inline stream decompressor.
  43
  44 The "IO" classes implements the specific parts of the stream. This could be
  45 nothing in the case of wxMemoryIn/OutputStream which bases itself on
  46 wxStreamBuffer. This could also be a simple link to the a true syscall
  47 (for example read(...), write(...)).
  48
  49 \wxheading{Generic usage: an example}
  50
  51 About its usage, it's simple. We can take the example of wxFileInputStream and here is a sample
  52 code:
  53
  54 \begin{verbatim}
  55  ...
  56  // The constructor initializes the stream buffer and open the file descriptor
  57  // associated to the name of the file.
  58  wxFileInputStream in\_stream("the\_file\_to\_be\_read");
  59
  60  // Ok, read some bytes ... nb\_datas is expressed in bytes.
  61  in\_stream.Read(data, nb\_datas);
  62  if (in\_stream.LastError() != wxStream\_NOERROR) {
  63    // Oh oh, something bad happens.
  64    // For a complete list, look into the documentation at wxStreamBase.
  65  }
  66
  67  // You can also inline all like this.
  68  if (in\_stream.Read(data, nb\_datas).LastError() != wxStream\_NOERROR) {
  69    // Do something.
  70  }
  71
  72  // You can also get the last number of bytes REALLY put into the buffer.
  73  size\_t really\_read = in\_stream.LastRead();
  74
  75  // Ok, moves to the beginning of the stream. SeekI returns the last position
  76  // in the stream counted from the beginning.
  77  off\_t old_position = in\_stream.SeekI(0, wxFromBeginning);
  78
  79  // What is my current position ?
  80  off\_t position = in\_stream.TellI();
  81
  82  // wxFileInputStream will close the file descriptor on the destruction.
  83 \end{verbatim}
  84
  85 \wxheading{Compatibility with c++ stream}
  86
  87 As I said previously, we could add a filter stream so it takes an istream
  88 argument and builds a wxInputStream from it: I don't think it should
  89 be difficult to implement it and it may be available in the fix of wxWindows 2.0.