Thread: modify txt file in C

  1. #1
    Registered User
    Join Date
    Dec 2007

    modify txt file in C

    hi everyone,
    i met some problem in this.
    i used fseek to locate position prepared to be written.
    for example,
    while time will be users input.

    the content of the txt file to be modified

    aabb, ccddeeff, 30gghhiijjkk

    obvious the string 30(at byte position 16)
    is going to be changed.
    but if users input were 3000
    then gg(position 18) will be overwrote.
    i will get the result
    aabb, ccddeeff, 3000hhiijjkk

    but all i need is

    aabb, ccddeeff, 3000gghhiijjkk

    or EVEN users input were 300000
    i still need the result to be

    aabb, ccddeeff, 300000gghhiijjkk

    how to do it?

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    You read the file line by line
    You change each line to suit
    You write the line to a new temporary file.

    When you're done, close both files, delete the original and rename the temporary.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

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