A simple file I/O problem

This is a discussion on A simple file I/O problem within the C Programming forums, part of the General Programming Boards category; Hi all, I have a simple file I/O query. I have opened a new file for writing, I write it ...

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    A simple file I/O problem

    Hi all,
    I have a simple file I/O query. I have opened a new file for writing, I write it to some point then decide to go back to a particular point and write there again.
    What I am doing is that I am storing the position I want to write at later, in a variable using fseek function. But later when I try to write at that position the text there is overwritten rather than getting inserted. so the problem is how to insert the text using C.

    Thanks a lot

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    Sr. Software Engineer filker0's Avatar
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    Quote Originally Posted by eecoder
    ...
    But later when I try to write at that position the text there is overwritten rather than getting inserted. so the problem is how to insert the text using C.
    The simple answer is that this is not how I/O works on files using the standard C file I/O functions. Writing always overwrites or extends the file, but never moves stuff around within the files.
    Insert obnoxious but pithy remark here

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    Rabble Rouser Slacker's Avatar
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    >so the problem is how to insert the text using C.
    You need to rewrite the entire file, inserting the lines you want as necessary during the rewrite. Unless your system supports record oriented files, you can't insert and shift everything after forward, or delete and shift everything after back.

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    Does cpp support insertion and deletion of lines or text??

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    ATH0 quzah's Avatar
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    File manipulation is handled the same in both. The only reason it seems like you're editing the middle of a file, is because the whole thing is loaded into memory in your text editor of choice, and rewritten when you press the "save" button.


    Quzah.
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    ok, and thank you all.

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    There is one way in which you can insert the text in between. You can initaly write some fake taxt at the place where you want to write, this mite not be usefull always, as u may not always be able to tolerate junk data in a file, but in some cases it may be usefull as you will not have to write the whole file again. This was the trick i was using, but wanted to know if there was any better way.
    Well thanks

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    Sr. Software Engineer filker0's Avatar
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    using lseek() followed by write() will overwrite existing text, yes, but this is not insertion, it's replacement.
    Insert obnoxious but pithy remark here

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    yes it is replacement, but you could have written some junk data at the place where you have to write later. If you know the length of string you have to write later.

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    Well to do this you would require to push all characters on and ahead of the insertion 1 char ahead. Leaving you with a blank space to type in. This could be done with some work.
    If its I/O to a file then it could be troublesome tho..
    Who needs a signature?

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    That post is about 4 years old Nathan - best to let the Zombie's sleep on.

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