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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: problem with fread/fwrite
Keywords: fread, fwrite, file pointers
Message-ID: <14384@smoke.brl.mil>
Date: 7 Nov 90 12:05:56 GMT
References: <402@bally.Bally.COM>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 15

In article <402@bally.Bally.COM> siva@bally.Bally.COM (Siva Chelliah) writes:
-  fp = fopen("temp.dat","r+b");
-  fread(tbuf,sizeof(tbuf),1,fp);
-  fwrite(buf,sizeof(buf),1,fp);
-line 0line 1line 2line 3line 4line 0line 4
-Can you believe this?

Sure.

-When I used fseek before fwrite, it worked.  I do not remember reading 
-anywhere that I should do a fseek before fread/fwrite.

The exact requirement is spelled out quite explicitly in the C standard,
section 4.9.5.3.  I won't bore you with the technical reasons, but this
was not an oversight nor necessarily sloppiness on the part of your C vendor.