Comments on: C Tutorial – Binary File I/O

By: C Tutorial – Binary File I/O | CodingUnit Programming Tutorials | FRANCESCO DI FUSCO

Wed, 16 Nov 2011 13:37:19 +0000

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By: Alan

Alan — Sat, 06 Aug 2011 19:09:44 +0000

This was an extremely helpful tutorial. Thank you so much.

I understand that fseek() offsets the pointer by characters. Is there anyway I can offset the pointer by ‘n’ number of lines? I’m trying to write/overwrite a string to a specific line in my text file. I tried

fprintf(myfile+3, “www.codingunit.com”);

but it does not offset my pointer to line 3 in my textfile. Please enlighten me with your wisdom, great one.

Thanks again!
Alan

By: isaiah

isaiah — Thu, 04 Aug 2011 12:06:54 +0000

tnx for some example of the program tnx a lot….more power

By: admin

admin — Sat, 14 May 2011 12:40:23 +0000

@mohammed – It’s very easy to use variables y and z in the first write and read examples. You just have to add some additional lines. The examples now only uses the variable x to keep the examples smaller. To use all three (x,y,z) variables add the following lines to the examples:

Write for loop:
for ( counter=1; counter <= 10; counter++) {
my_record.x= counter;
my_record.y= counter;
my_record.z= counter;
fwrite(&my_record, sizeof(struct rec), 1, ptr_myfile);
}

The read example:
for ( counter=1; counter <= 10; counter++) {
fread(&my_record,sizeof(struct rec),1,ptr_myfile);
printf(“%d\n”,my_record.x);
printf(“%d\n”,my_record.y);
printf(“%d\n”,my_record.z);
}

As you can see we only have to fill the other two variables (y and z) as we did with x variable. Then we can read them as we did x in the read example.

Hope this helps!

By: mohammed

mohammed — Fri, 13 May 2011 07:15:12 +0000

the first example in the web page only writes to variable x? how to write and read using variable y and z?

By: Sandeep Kumar

Sandeep Kumar — Sat, 26 Feb 2011 17:57:39 +0000

I want to store a character array data (89 bytes) to a binary file. Please send the fwrite function code for this. Is it possible to store current PC time to same binary file?

Thanks,
Sandeep

By: Pratap

Pratap — Sat, 22 Jan 2011 01:07:28 +0000

I want to dump some memory into a file, a complex structure which contains pointers to list etc, and again want to set the same memory from this file.

Is it possible to do with fwrite & fread functions

By: admin

admin — Thu, 09 Dec 2010 08:11:12 +0000

@radix: the goal of that example is to show how to use of the rewind() function. That’s why the end of the file is searched (otherwise there is nothing to rewind from) and then rewind() is called to go to first position of the file.

You will get garbage if rewind isn’t called because the for loop will try to read records beyond the end of the file, because there is no check performed to check if the end of the file has been reached.

So again it’s just to show the use of the rewind() function: nothing more, nothing less. The search for the end of the file is only done, so we that we can rewind.

By: radix

radix — Wed, 08 Dec 2010 15:25:13 +0000

In your last example you do the following…

fseek(ptr_myfile, sizeof(struct rec), SEEK_END);
rewind(ptr_myfile);

And mention that you get garbage without the rewind. If you seek to the end of file and then offset beyond the end of the file, you will be reading garbage, you need a negative offset.

These 2 lines are pointless in your example. Or am I mistaken?

By: John

John — Fri, 06 Aug 2010 12:05:22 +0000

I’ve seen people read 1 byte at a time, then if you need it to be one number just multiply it by it corresponding position…

first number n*10000
+ second number n*1000
+ third number n*100
+ forth number n*10
+ fifth number n..

I’m not a professional so please research for better ways.