Re: [Mingw-users] ifstream read() results in wrong gcount and eof for CR+LF terminated files

[Danny S. <dan...@cl...>]

----- Original Message ----- 
From: "Earnie Boyd" 
Sent: Friday, 13 January 2006 11:26


> Quoting Ronald Lamprecht <R.Lamprecht@T-Online.de>:
> 
> > Hi,
> >
> > Using the current mingw3.4.2 the following simple example used with a
> > Windows CR+LF lineterminated testfile of more than 512 bytes results in
> > wrong gcount() and eof():
> >
> >     std::ifstream ifs("my_cr_lf_file.txt");
> >     std::vector<char> dest;
> >     int blocksize = 512;
> >     size_t len = 0;
> >     int nread=0;
> >     do {
> >         dest.resize(dest.size() + blocksize);
> >         is.read (&dest[len], blocksize);
> >         nread = is.gcount();
> >         len += nread;
> >     } while (nread == blocksize);
> >
> > If the testfile consists of 17 lines within the first 512 bytes
> > gcount() will return 495 and eof() will be true after the first read()
> > call. Looks like a problem with CR+LF to LF convertion in read().
> >
> > I found the following hint in this mailing list that was missing details
> > and code examples:
> >
> 
> Microsoft when creating MSDOS introduced your problem.  If the i/o 
> channel is in ``text mode'' the read will return a count of one less 
> than actually read if the lines of the file end with \r\n.  Set your 
> file descriptor to ``binary mode'' to correct the issue or use the 
> dos2unix utility to change the file to \n line endings instead of \r\n.
> 

Actually, fstream should still work correctly in text mode.  This was 
 PR libstdc++/20806.  It is fixed in gcc-3.4.5. No need to use binary mode.
Danny

> Earnie Boyd
> 
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