Sequence IO
Sequences or streams (not to be confused with c++ streams) of
objects are accessed in RAVL with two classes DPIPortC<> and DPOPortC<>
. DPIPortC allows sequences of objects to be read in to a
program and DPOPortC is used for writing them out. You can
initialise streams with the OpenISequence
and OpenOSequence
respectively.
A typical example of where this kind of IO is used is the processing of video
sequences Ravl.Images.Video.
Following is a example of how to use these classes for reading
and writing a sequence of integers.
Before you can do anything you need to include the following header:
#include "Ravl/DP/SequenceIO.hh"
You also have to include the appropriate library for handling the
sequences you wish to use. e.g. For video IO you needs to add
RavlVideoIO to your USESLIBS line in the
defs.mk.
Reading a sequence
DPIPortC<int> in;
if(!OpenISequence(in,"myfile.abs")) {
// Failed to open input file.
// Report an error...
}
int value;
while(in.Get(value)) {
// Process your data...
}
Writting a sequence
DPOPortC<int> out;
if(!OpenOSequence(out,"myfile.abs")) {
// Failed to open output file.
// Report an error..
}
for(int i = 0;i < 10;i++)
out.Put(i); // Write some data.
Numbered files
It is possible to open a series of numbered files as a
sequence. This can be done in several ways, by opening the first
file in the sequence, by open with a filename containing %d in
place of the number or if the number is before the extension by
omitting the number entirely. See the sub-section Numbered files
for more details.
Type conversion
The same system of type conversion is used for streams as for
the loading and saving of single objects. For more details on
how this works and how to implement type converters see Ravl.Core.IO.
Seekable streams
Often you want both information about where in the stream you
are, and control over the position from which your going to read
or write data. This can be done with seekable streams DPISPortC<> and
DPOSPortC<>
. They can be used and initalised in the same way as
DPIPortC and DPOPortC seen previously with OpenISequence
and OpenOSequence.
These classes have an additional set of member functions which
allow control of the position in the stream. A description of
these functions can be found in DPSeekCtrlC. Note: not
all streams support all these methods, if a sequence doesn't
support a method your using it will report a failure. It is
possible to open any sequence in RAVL as a seekable stream,
though the seek controls will have no effect.
Normal functions:
OpenOSequence(DPOSPortC &,const StringC &,const StringC &,bool) | Open a seekable output stream. |
OpenISequence(DPISPortC &,const StringC &,const StringC &,bool) | Open a seekable input stream. |
OpenOSequence(DPOPortC &,const StringC &,const StringC &,bool) | Open a normal output stream |
OpenISequence(DPIPortC &,const StringC &,const StringC &,bool) | Open a normal input stream |