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ccharhexbitwise-and

bitwise-and with HEX and CHAR in C

I'm really getting frustrated here. Trying to implement the CRC-CCITT algorithm and I found a very nice example on an Internet site.

There is one line whose output I completely don't understand:

unsigned short update_crc_ccitt( unsigned short crc, char c){
[...]
short_c  = 0x00ff & (unsigned short) c;
[...]
}

I want to calculate the CRC of the "test" string "123456789". So in the first run the char 'c' is 1. From my understanding short_c from the first run should be equal to 1 as well, but when I print it to the console, I get short_c = 49 for c = 1. How?

0x00ff in binary is: 1 1 1 1 1 1 1 1 
char 1 in binary is: 0 0 0 0 0 0 0 1
bitand should be   : 0 0 0 0 0 0 0 1

Where is my mistake?

Solution

  • The character 1 has ASCII code 0x31 = 49. This is different from the character with ASCII code 1 (which is ^A).