NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/12245

Internet Message Format | 1996-08-05 | 2.4 KB

Path: anvil.ugrad.cs.ubc.ca!not-for-mail
From: [e-mail] (Kazimir Kylheku)
Newsgroups: comp.lang.c
Subject: Re: Need help with a STRING that won't go away!!!
Date: 29 Mar 1996 15:07:59 -0800
Organization: Computer Science, University of B.C., Vancouver, B.C., Canada
Message-ID: <[e-mail]>
References: <4jh7e2$[e-mail]> <[e-mail]>
NNTP-Posting-Host: anvil.ugrad.cs.ubc.ca

In article <[e-mail]>,
The Amorphous Mass  <[e-mail]> wrote:
 >On 29 Mar 1996, George Hauser wrote:
 >
 >> In this program I am interested in processing unti the EOF, when
 >> I get to it I don't want to loop again to avoid dumping the
 >> data that still is in the string (line).
 >>
 >> As it is, it dumps the exact same record that was on the last line twice!
 >> This causes the import to POST an OCEAN FREIGHT amount 2x!!!
 >
 >  You fell in one of the pitfalls awaiting unsuspecting Pascal programmers.
 >  Since feof(stream) only tells you that your last read on stream
 >returned EOF, the following loop structure doesn't work the way it does
 >in Pascal:
 >
 >  while (!feof(stream1))
 >  {
 >    fgets(line, stream1);
 >    fputs(line, stream2);
 >  }

And with good reason. You see, on many operating systems, it's difficult to
tell whether you are at the end of the file until you actually attempt to
_read_ past the end of the file. C's stdio logic is probably easier to
implement because it reflects that.

You try the read, and then if you fail you return EOF.

 >  What you want is:
 >
 >  while (fgets(line, stream1))
 >    fputs(line, stream2);
 >
 >  since fgets() returns NULL when it hits EOF.  This reads "while fgets()
 >reads valid input, fputs() the string read by fgets()."

That's probably not the most appropriate way since fgets is used for line-mode
input. For a raw copy, you might want to do an unbuffered fread()/fwrite() or a
getc()/putc() loop. The latter is loop is efficient because it copies data
directly between one stream's buffer and another (getc/putc are frequently
implemented as macros, or are inlined by the compiler so doing it a character
at a time may actually be quite efficient). With fgets() or fread()/fwrite(),
you are putting the data through an intermediate ``bounce buffer'' rather than
pumping it directly between two streams.
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