以十六进制表示位字符串的最佳实践（Arduino）

Question

I have a string (or cstring) consisted of 24 bits "000101011110011110101110" that should be represented in hex (0x15e7ae).

As i understand bit string needs to be splitted on to 6 parts by 4 bits "0001 0101 1110 0111 1010 1110" and then each part converted to hex

0001 -> 1
0101 -> 5
1110 -> e
0111 -> 7
1010 -> a
1110 -> e

So what are the simplest and cost effective ways to convert it to hex representation: 0x15e7ae?

There is also dilemma for me which string type is better to use String or char[]. String can be easily splitted using substring function, but i don't know how to convert string type to hex.

And contrariwise char[] can be easily converted to hex using strtoul function but i didn't find simple way to split char string.

Answer 1

This is quite literally found in this link: StringConstructors

 // using an int and a base (hexadecimal):
 stringOne =  String(45, HEX);   
 // prints "2d", which is the hexadecimal version of decimal 45:
 Serial.println(stringOne);   

Answer 2

const char* binary = "000101011110011110101110" ;
char hex[9] = "" ;

uint32_t integer = 0 ;

for( int i = 0; binary[i+1] != '\0'; i++ )
{
    if( binary[i] == '1' )
    {
        integer |= 1 ;
    }
    integer <<= 1 ;
}

sprintf( hex, "0x%06x", integer ) ;

Answer 3

Let's try some simple bit shifting.

std::string sample_str = "000101011110011110101110";
uint32_t result = 0;
for (unsigned int i = 0; i < sample_str.length(); ++i)
{
  result = result << 1;
  result = result | (sample_str[i] & 1);
}

There may be faster methods, but you would have to search the web for "bit twiddling string".

Background
This is based on the assumption that the character representation of zero has the least significant bit set to zero. Likewise the character representation of one has the least significant bit set to one.

The algorithm shifts the result left by one to make room for a new bit value. Taking the character value and ANDing with 1 results in a value of zero for '0' and one for '1'. This result is ORed into the result value, to produce the correct value.

Try single stepping with a debugger to see how it works.

Answer 4

In C, this is quite simple. Use strtoumax(binary, 0, 2) to convert your binary string to an uintmax_t and then convert that to a hex string with sprintf or fprintf .