negative offset

Discussion in 'C' started by markyjj, Dec 8, 2005.

  1. markyjj

    markyjj New Member

    Dec 7, 2005
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    Could someone please help me with the following code:

    Inout_file.seekp(((long)-1 * sizeof(int)), ios::cur);
    // offset // // mode//

    This code is used to move the offset back 4 bytes from the 12th byte after replacing a value in the list. The above offset is -4 in order to move the offset back and this results in the offset now being at the 8th byte. I cant understand why the offset is -4 though. Is this to do with the ‘long’ and what is the -1 for?. Also this code is worked on the basis that integers are 4 bytes.

    Hope that anyone can help…thanks
  2. shabbir

    shabbir Administrator Staff Member

    Jul 12, 2004
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    The seekp member function sets this pointer and thus provides random-access disk file output.

    Now about the code You are passing the first parameter as
    -1 * sizeof(int)
    Which is
    -1 * 4 [As you have told integer is 4 bytes]
    And so the result becomes
    -4 and so seekp moves the pointer 4 bytes in the reverse direction and so it moves from 12th to 8th byte.

    Shabbir Bhimani

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