C++ / Arduino: How do I convert a string/char-array to byte?

Question

I want to convert

char lineOneC[8] = {0,1,1,0,0,0,0,1};

into

byte lineOneB = B01100001;

How do I do this in C++ / Arduino?

Billy ONeal · Accepted Answer · 2010-12-06 19:12:52Z

6

I'm not sure about specific restrictions imposed by the Adruino platform, but this should work on any standard compiler.

char GetBitArrayAsByte(const char inputArray[8])
{
    char result = 0;
    for (int idx = 0; idx < 8; ++idx)
    {
        result |= (inputArray[7-idx] << idx);
    }
    return result;
}

A test of this code is now on Codepad, if that helps.

answered Dec 6, 2010 at 19:12

Billy ONeal

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DReJ · Accepted Answer · 2010-12-06 19:11:48Z

5

Just shift 0 or 1 to its position in binary format. Like this

char lineOneC[8] = {0,1,1,0,0,0,0,1}; 
char lineOneB = 0;
for(int i=0; i<8;i++)
{
    lineOneB |= lineOneC[i] << (7-i);
}

answered Dec 6, 2010 at 19:11

DReJ

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Nikolai Fetissov · Accepted Answer · 2010-12-06 19:11:07Z

4

char lineOneC[8] = { 0, 1, 1, 0, 0, 0, 0, 1 };
unsigned char b = 0;

for ( int i = 7; i >= 0; i-- ) {
    b |= lineOneC[i] << ( 7 - i );
}

answered Dec 6, 2010 at 19:11

Nikolai Fetissov

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Comments

Zac Howland · Accepted Answer · 2010-12-06 19:13:46Z

0

If you know that the values of your character array will always be either 1 or 0:

char line[8] = { '0', '1', '1', '0', '0', '0', '0', '1'};

unsigned char linebyte = 0;
for (int i = 7, j = 0; j < 8; --i, ++j)
{
    if (line[j] == '1')
    {
        linebyte |= (1 << i);
    }
}

answered Dec 6, 2010 at 19:13

Zac Howland

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Comments

Will · Accepted Answer · 2010-12-07 03:14:49Z

0

If the result is supposed to be B01100001, then byte 0 is the MSB (most significant bit), not byte 7 ...

char line[8] = { 0, 1, 1, 0, 0, 0, 0, 1 };
unsigned char b = 0;
for ( int ii = 0; ii < 8; ii++ )
{
  b <<= 1;
  b |= line[ii];
}

The other answers I've seen, if I read them correctly, put the MSB on byte 7.

EDIT: Fixed quotes; miscopied it before.

edited Dec 7, 2010 at 3:14

answered Dec 6, 2010 at 19:22

Will

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2 Comments

Billy ONeal Over a year ago

Did you actually try the code? That answer doesn't work because you quoted the numbers ('0' is not the same as 0). And the subindex 7 is the 8th item in the list in C and C derived languages, because arrays begin at element zero, not element one.

Will Over a year ago

Thanks for the quotes; for some reason when I copied it from my editor earlier (not copy/paste, but retyping it) I didn't realize that I quoted the values; force of habit from quoting them all the time. As for arrays begin at zero - yes, if you read what I put, I said "byte 0" and "byte 7"; I don't normally reference my array positions 1-based, so "byte 7" is actually the eighth character in the array.

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