filepointer

This is a discussion on filepointer within the C Programming forums, part of the General Programming Boards category; hi i work with text-files that i opened with fopen. i can get and restor the curent psoition by using ...

  1. #1
    Registered User stormbringer's Avatar
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    filepointer

    hi

    i work with text-files that i opened with fopen. i can get and restor the curent psoition by using fgetpos and fsetpos. but is it also possible to just move the pointer one element backward or forwar by simply incrementing the handle or something similar? always storing and setiting the position isn't too efficient i think. is it also possible to jump to a known position (for example i know that i just have to start with the 1000 st char) without just looping and reading char after char till 100 is reached?

    thanks

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    Registered User The Junglist's Avatar
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    fseek() is what you are looking for.

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    Confused Magos's Avatar
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    Use this:
    Code:
    fseek(MyFile, 1, SEEK_CUR);
    to go one step forward and this:
    Code:
    fseek(MyFile, -1, SEEK_CUR);
    to go one step backwards. Of course you can change 1 to some other value (constant or variable) if you want to move more than one step. Make sure you catch the return value to make sure no error occured, ie you move outside the bounds.
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    moi
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    Re: filepointer

    Originally posted by stormbringer
    hi

    i work with text-files that i opened with fopen. i can get and restor the curent psoition by using fgetpos and fsetpos. but is it also possible to just move the pointer one element backward or forwar by simply incrementing the handle or something similar? always storing and setiting the position isn't too efficient i think. is it also possible to jump to a known position (for example i know that i just have to start with the 1000 st char) without just looping and reading char after char till 100 is reached?

    thanks
    fseek () as had been already mentioned. incrementing the FILE pointer will do everything but what you want it to; it points to a struct that contains information about the file in question, and does not point to the data in the file at all.
    hello, internet!

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    Registered User stormbringer's Avatar
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    thanks everybody

    is there any document where i can see how the struct for tehe filepointer looks. i'm just interested, of course i'll use fseek.

  6. #6
    Registered User stormbringer's Avatar
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    that's something that makes me curious since a long time. the c standard is very simple, so the stuff like reading from strams and so on is provided by the compiler's .h files.
    1. the .h files just have definitions and so on. the source that actualy does something has to be in a .c file, doesn't it. so how does the compiler know where that .c file is and how the name is. there ain't something like a "note" in the .h file.

    2. are the routines that do stuff like opening io ports, sockets and so on writen in c or assembly or what? that would mean that they are very platform dependend. so the only thing making code portable ist, that for every platfor exist's a speciel compiler with special standard .h files.

    this all get's me a little bit confused.

  7. #7
    n_h
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    The C Runtime is the gate to platform independence. The Runtime itself calls for the specific OS routines (so you have the same programming interface on every platform). The Filepointer is an handle, which the OS needs to perform file operations (yes, there's a structure the OS has, but you can't modify it directly. Instead you modify it by using the OS specific file operation functions)

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