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bitfield?

oddboy (3)
hey gang,

i have a function in a library i'm trying to use. the function returns an int which is a bit field. i'd like to do a switch/case with the result in a loop to figure out what options are set, i.e. which bits are set.

the function returns a number like "128259" (as an int).

then i do something like this:

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result = getBitFiled();
for (i=0; i<15; i++) {
  if (result & i) {      // this is where i'm not sure what to do
     switch(i) {
        case: 0x01
        // do something
        // ....
        case: 0x100
        // do something
     }
   }
}


Any pointers?

thanks!

maeriden (872)
You can try something like this, but it's untested and my knowledge on bit fields is scarce, so you might want to wait for an answer from a more experienced person
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result = getBitFiled();
// 0 is the absence of flags
for(i = 1; i <= last_flag_value; i << 1)
{
  switch(result & i)
  {
    case 0:  // The bit is turned off. It's the same as if(result & i == false)
      break;
    case 0x01: // or case OPTION_ONE
      break;
    case 0x02:
      break;
    // Etc
  }
}
naraku9333 (2163)
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result = getBitFiled();
// 0 is the absence of flags
for(i = 1; i <= last_flag_value; i << 1)
{
    If(result & i)
    {
        //bit is set
    }
    else
    {
        //not set
    }
}


The and will result in either 0 or 1 only.
Last edited on
Stewbond (2827)
I'm guessing that each bit will require us to do something different, so a loop doesn't really help us: 
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result = getBitFiled();
if (result & 0x01)
  // do something
if (result & 0x02)
  // do something
if (result & 0x04)
  // do something
if (result & 0x08)
  // do something
if (result & 0x10)
  // do something
if (result & 0x20)
  // do something
if (result & 0x40)
  // do something
if (result & 0x80)
  // do something


I think there are occasions where loops are over-used. I've edited the following out of code I saw just the other day:
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for (int i = 0; i < 2; i++)
{
  switch(i)
  {
  case 0:
    // do something
    break;
  case 1:
    // do something else
    break;
  }
}
 
Edited result:
// do something
// do something else
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