Thread: bit clearing problem

  1. #1
    Registered User
    Join Date
    May 2005

    bit clearing problem

    I'm using the following code to clear a bit in position pos (starting with position 0 on the far right) in the integer value. (Please don't comment on the stupidity of the code writing right now). When I give it an input of 15 and 1 it gives me some massively negative number (-2147483639) as the return value while it should be returning 13
    (clearing the first bit would effectively subtract two from the original value)
    Any ideas on why this is not working properly?
    unsigned int IBCLR(int value, int pos)
        unsigned int tempval = (unsigned)value;
        unsigned int temppos = (unsigned)pos;
        return tempval & (~((unsigned)1 << temppos));

  2. #2
    Join Date
    Mar 2005
    I know you said not to clean it, but I rewrote it to make sure it was correct...

    I got 13 with this code:
    #include <iostream>
    using namespace std;
    unsigned IBCLR (unsigned value, unsigned pos)
        return value & (~(1U << pos));
    int main () {
       cout << IBCLR (15, 1) << endl;
    Yes, your code works.
    Last edited by JoshR; 07-19-2005 at 05:31 PM.

  3. #3
    Registered User Codeplug's Avatar
    Join Date
    Mar 2003
    >> it gives me some massively negative number
    And yet your return type is are you getting a negative number?

    Your code looks fine to me.


  4. #4
    ATH0 quzah's Avatar
    Join Date
    Oct 2001
    Let's see his call to it. Possibly something like this?
    unsigned int myfunction( ... );
    int x;
    x = myfunction( somestuff );

    Hope is the first step on the road to disappointment.

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