stream converting

[Moritz Tacke]

Hi there!

I have a problem concerning the file input to a c++ program: the
expected input is either in binary or in some kind of text format;
what I finally want is the binary version.
I know how to translate between these two versions and would like to
write some kind of wrapper. This wrapper should open the text file and
provide an istream which behaves exactly like the ifstream of an
equivalent binary file would. Is there a smart way to do this?
Greetings,
Moritz

 

[Mike Wahler]

Hi there!

I have a problem concerning the file input to a c++ program: the
expected input is either in binary or in some kind of text format;
what I finally want is the binary version.
I know how to translate between these two versions and would like to
write some kind of wrapper. This wrapper should open the text file and
provide an istream which behaves exactly like the ifstream of an
equivalent binary file would. Is there a smart way to do this?

No 'wrappers' or 'smartness' required:

std::ifstream input("myfile.txt", std::ios::binary);

-Mike

 

[Moritz Tacke]

No 'wrappers' or 'smartness' required:

std::ifstream input("myfile.txt", std::ios::binary);

-Mike

Well, it looks like I didn't express myself correctly: the binary
format and the "text"-format are qualitatively different. The text
format is some kind of encoding of the binary one, where four bytes of
"text" are used to encode three bytes of the "binary".
What I am trying to do right now is to write some kind of wrapper
which reads the four "text"-bytes and converts them to the three
corresponding binary-bytes; this wrapper should be used by the other
parts of the program as if it was an ifstream which directly reads the
binary file.

Hm. I hope I did succeed in formulating the point this time...
Greetings!
Moritz

 

[Ivan Vecerina]

....
| > std::ifstream input("myfile.txt", std::ios::binary);
....
| Well, it looks like I didn't express myself correctly: the binary
| format and the "text"-format are qualitatively different. The text
| format is some kind of encoding of the binary one, where four bytes of
| "text" are used to encode three bytes of the "binary".
| What I am trying to do right now is to write some kind of wrapper
| which reads the four "text"-bytes and converts them to the three
| corresponding binary-bytes; this wrapper should be used by the other
| parts of the program as if it was an ifstream which directly reads the
| binary file.
Hi Moritz,

The way to do what you are looking for is to implement a custom
streambuf class (the polymorphic buffering class which handles
the i/o behind any standard stream). Your implementation
of this file would generate the buffer by translating data
read from another stream.
For some examples, you may check Dietmar Kühl's website:
http://www.informatik.uni-konstanz.de/~kuehl/
Dietmar authored part of Josuttis' (excellent) book
"The C++ Standard Library - A Tutorial and Reference" (in particular
sections related to the i/o stream library), a valuable reference.

But I think that you would be picking the wrong level of
abstraction by working at the level of the streams.
It would probably be better to define a higher-level
interface (abstract base class) to read the contents
of a file, and implement it for both the ascii and binary
file formats.
Then, if needed, you can do the same to write both
formats, and -- if needed -- perform a translation
on-the-fly.


Regards,
Ivan