Re: Reading a file.
On Jul 16, 10:47 pm, "BobR" <removeBadB...@worldnet.att.net> wrote:
<szcl...@googlemail.com> wrote in message...
Right, I have managed to read the file it's all ASCII characters, I've
realised that I need to read some stupid hand book to find out which
bytes need to be read or something... Anyway, is there a way I can
extract readable text from the file and write it to a text file? It
asks me to "Extract the administrative message contained within the
last 800 bytes of the Interpretation Block and write it to a disk file
called Admin.txt" I can see this piece of text when I compile the
program.
[...]
std::ifstream in( "filename.txt" );
The file is opened in text mode.
in.seekg( -800, std::ios::end ); // may need adjust for '\n'
So this is illegal.
The simplest way to do this is just to read the entire file into
a variable (std::string or std::vector< char >), then write it,
e.g.:
std::string s( (std::istreambuf_iterator< char >( in )),
(std::istreambuf_iterator< char >()) ) ;
std::copy( s.end() - std::min( s.size(), N ),
s.end(),
std::ostreambuf_iterator< char >( out ) ) ;
This can quickly become very slow, however, or even fail, if the
file is large. (I regularly have to deal with log files of
hundreds of megabytes; I do *not* use this solution for them.)
The alternative is to open the file in binary mode, so you can
seek however you want in it.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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