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read_bit

Posted on 2001-07-12
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Last Modified: 2008-02-01
Iam have program in C++Builder and I want to read specific bit in String Can I do that and how??
exmple(A=(1000001)bin I want to know the fouth bit is 0 or the last bit is 1)
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Question by:aminmohsalih
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nietod earned 30 total points
ID: 6277754
You will need to obtain the byte that the bit is stored in, then extract the bit from there with operator &.

example follows.
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Expert Comment

by:nietod
ID: 6277786
Thsi function miight be useful to you

const itn BitPerChr = 8*sizeof(char); // Might need to be changed
                          // for machines that don't store 8 bits per byte.

bool TestStringBit(const char *Str, // string to extract from.
                        int BitNum)   // 0-based bit number of bit to extract.
{
    int BytNum = BitNum / BitPerChr;
    BitNum %= BitPerChr;

   assert(BytNum < strlen(Str)); // Might want this as a permenant test.
   int Byt = Str[BytNum];  // Get desired byte.
   int Msk = 1 << (BitNum-1);  // mask for the desired bit.

   return (Byt & Msk) != 0;
}
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