EOF Problem

[sugaray]

hi, the problem i'm having here is that after i've written
10 integers to a disk file, the reading process always output
one more integer than was in the file.

===========snippet for write ===========
int i;
FILE *fp;
fp=fopen("number","a+b");

for(i=0;i<10;++i)
fwrite(&i,sizeof(int),1,fp);

fclose(fp);

========== snippet for read ===========
int i;
FILE *fp;
fp=fopen("number","rb");

while(!feof(fp)){
fread(&i,sizeof(int),1,fp);
printf("%d\n",i);
};

fclose(fp);
=======================================

thanx for your help !

 

[Lew Pitcher]

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hi, the problem i'm having here is that after i've written
10 integers to a disk file, the reading process always output
one more integer than was in the file. [snip]
========== snippet for read ===========
int i;
FILE *fp;
fp=fopen("number","rb");

while(!feof(fp)){
fread(&i,sizeof(int),1,fp);
printf("%d\n",i);
};

fclose(fp);
=======================================

feof() only returns true /after/ you've read past end-of-file

Consider the following:
Assume that your file contains one (and only one) integer. Your program does
the following:
a) fopen the file
b) test if we have encountered eof on the file (feof())
c) because feof() is not true (we haven't read past eof yet)
fread() the first and only integer.
d) print integer
e) test if we have encountered eof on the file
f) since we haven't yet read past end-of-file (we're right /before/
end-of-file) feof() didn't return true, so we
fread() the second (non-existant) integer (this fails, silently, but also
now positions us such that we have /now/ read past eof)
g) print integer
h) test if we have encountered eof on the file
i) since we /have/ read past eof, we exit the loop
j) fclose
k) terminate





- --
Lew Pitcher

Master Codewright & JOAT-in-training | GPG public key available on request
Registered Linux User #112576 (http://counter.li.org/)
Slackware - Because I know what I'm doing.
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[Artie Gold]

hi, the problem i'm having here is that after i've written
10 integers to a disk file, the reading process always output
one more integer than was in the file.

===========snippet for write ===========
int i;
FILE *fp;
fp=fopen("number","a+b");

for(i=0;i<10;++i)
fwrite(&i,sizeof(int),1,fp);

fclose(fp);

========== snippet for read ===========
int i;
FILE *fp;
fp=fopen("number","rb");

while(!feof(fp)){
fread(&i,sizeof(int),1,fp);
printf("%d\n",i);
};

fclose(fp);
=======================================

See: http://www.eskimo.com/~scs/C-faq/q12.2.html

(you *did* read the FAQ before posting, didn't you? ;-))

HTH,
--ag

 

[CBFalconer]

hi, the problem i'm having here is that after i've written
10 integers to a disk file, the reading process always output
one more integer than was in the file.

===========snippet for write ===========
int i;
FILE *fp;
fp=fopen("number","a+b");

for(i=0;i<10;++i)
fwrite(&i,sizeof(int),1,fp);

fclose(fp);

========== snippet for read ===========
int i;
FILE *fp;
fp=fopen("number","rb");

while(!feof(fp)){
fread(&i,sizeof(int),1,fp);
printf("%d\n",i);
};

fclose(fp);
=======================================

The problem is failure to read the faq, in particular 12.2. Try:

while (fread(&i, sizeof (int), 1, fp)) printf("%d\n", i);

--
Some useful references:
<http://www.ungerhu.com/jxh/clc.welcome.txt>
<http://www.eskimo.com/~scs/C-faq/top.html>
<http://benpfaff.org/writings/clc/off-topic.html>
<http://anubis.dkuug.dk/jtc1/sc22/wg14/www/docs/n869/> (C99)

 

[Emmanuel Delahaye]

hi, the problem i'm having here is that after i've written
10 integers to a disk file, the reading process always output
one more integer than was in the file.

It's a FAQ.

while(!feof(fp)){

Can you name the book or the school/course that taught that to you ? They
desserve to burn in hell.