how to read a binary file backwards?

This is a discussion on how to read a binary file backwards? within the C Programming forums, part of the General Programming Boards category; I am writing a file in binary using fwrite. I am opening this file for read and write. After each ...

  1. #1
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    how to read a binary file backwards?

    I am writing a file in binary using fwrite. I am opening this file for read and write. After each write, the file pointer points to the end of the file, and I need to be able to read backwards x number of bytes.

    I could move the pointer backwards X bytes, and then do a forward read (I would prefer this way), but I'm not sure how to do this either.

    Any suggestions?

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    Look into fseek. It has a way to reference from the beginning of the file, the end of the file or the current position. One of the latter two methods should work for you.

  3. #3
    Gawking at stupidity
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    Check out fseek(3): reposition stream - Linux man page. Example: fseek(fp, sizeof(record), SEEK_CUR);
    If you understand what you're doing, you're not learning anything.

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    fseek seems to be exactly what I'm looking for! Thanks so much, again!!

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    With fseek, there's no way to go backwards from the end is there?

    For example, the current pointer is at the end, and I know I need the last 4 bytes back. Can i just go back 4 bytes?

    It seems that I have to start from the very start and go forward total_bytes - 4bytes?

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    maybe I have to a combination of fgetpos and fsetpos

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    a_capitalist_story
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    If forward is positive, what would backwards be?

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    Some times, I'm smart. Others, the -1 of smart.

    It works. Thanks you lol.

  9. #9
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    Quote Originally Posted by dayalsoap View Post
    With fseek, there's no way to go backwards from the end is there?

    For example, the current pointer is at the end, and I know I need the last 4 bytes back. Can i just go back 4 bytes?

    It seems that I have to start from the very start and go forward total_bytes - 4bytes?
    Read the docs... There are in fact three options for seeking in a file... SEEK_SET relative to the beginning of the file, SEEK_CUR relative to the current position and SEEK_END relative to the end of the file...

    Reading is good....

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