Experts please find the cause of infinite loop

i have an infinte loop that i cant find the cause.The terminating condition should be end of file .

Code:

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  FILE *f;
f=fopen("office.out","r+");
position=ftell(f);
 
  while(!feof(f))
    {
    fread(&p,sizeof(struct office),1,f);
    makeRecords(&p);
    fseek(f, position *( sizeof(struct office)),SEEK_SET);
    fwrite(&p, sizeof(struct office),1,f);
   
    position++;
    printf("am here"); }
    fclose(f);

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Your answer lies here : Cprogramming.com FAQ > Why it's bad to use feof() to control a loop

Look closely at your code ....
Keep close track of what you are reading, where you are seeking to and what you are writing...
You will never hit the end of the file because the file keeps getting bigger.
Any EOF indication you may have gotten with your fread() call is reset by your fwrite() call.
If you don't hit the end of the file on a READ operation, the loop never ends.

Also you don't even check to see if the file actually opened or not.

Quote:

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Originally Posted by CommonTater

Look closely at your code ....
Keep close track of what you are reading, where you are seeking to and what you are writing...
You will never hit the end of the file because the file keeps getting bigger.
Any EOF indication you may have gotten with your fread() call is reset by your fwrite() call.
If you don't hit the end of the file on a READ operation, the loop never ends.

Also you don't even check to see if the file actually opened or not.

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i am honestly looking through my code but cant find what am doing wrong.How does my file increase in size when am using fwrite which overwrites the content in the file

Throw in a printf() for debugging and see what 'position' is equal to.

Quote:

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Originally Posted by sigur47

i am honestly looking through my code but cant find what am doing wrong.How does my file increase in size when am using fwrite which overwrites the content in the file

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Ok so you do fread() and it hits the end of the file...
Now you write to the file at a higher postion... position * sizeof(struct) ...
the file gets bigger and the EOF flag is reset
Now you come back to the top of your loop... what's it testing for?

EOF is only signalled after a read operation fails against the end of the file.
Writing to the file resets the flag.
Seeking resets the flag (yes, you can seek past the end of the file).

Quote:

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Originally Posted by CommonTater

Ok so you do fread() and it hits the end of the file...
Now you write to the file at a higher postion... position * sizeof(struct) ...
the file gets bigger and the EOF flag is reset
Now you come back to the top of your loop... what's it testing for?

EOF is only signalled after a read operation fails against the end of the file.
Writing to the file resets the flag.
Seeking resets the flag (yes, you can seek past the end of the file).

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Hi i have just tested my freads .Basically i have a file that contains 12 structures and after the 12th structure fread should return a 0 but mine returns a 1

Quote:

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int finished=9;
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
finished=fread(&p,sizeof(struct office),1,f);
printf("%d\n",finished);

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> Basically i have a file that contains 12 structures and after the 12th structure fread should return a 0 but mine returns a 1
Yes, that is correct.

You have to attempt to read record 13 before fread() will fail, and feof() will become true.

Quote:

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Originally Posted by Salem

> Basically i have a file that contains 12 structures and after the 12th structure fread should return a 0 but mine returns a 1
Yes, that is correct.

You have to attempt to read record 13 before fread() will fail, and feof() will become true.

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yes salem your right but if you look at the last code i posted ,my fread is on 13 and still no failure thats my question?

hi
I think you are reading from "office out" in r+ mode,and your writing to the same file.so it will be a infinite loop..because when write to the same file it will again not reaching EOF.
i think so..if any mistake forgive me..

fread returning 0 wen it fail to read ,so better you have to check it ,for come out of the loop .

Quote:

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Originally Posted by sigur47

yes salem your right but if you look at the last code i posted ,my fread is on 13 and still no failure thats my question?

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Read or RE-read messages 3 and 6 in this thread...

Writing to the file resets the EOF flag.