Convert string containing decimal digit to unsigned char

Question

I have an array of char (string) that contain a decimal number. How do I convert it to unsigned char?

char  my_first_reg[2];
memcpy( my_first_reg, &my_str_mymatch[0], 1 );
my_first_reg[1] = '\0';
// now my_first_reg contain reg number ... how to convert to unsigned char

Why not `my_first_reg[0] = my_str_mymatch[0]`? Seems simpler with out using `memcpy` — Ed Heal, Feb 05 '16 at 22:03
Possible duplicate of [C - char isn't converting to int](http://stackoverflow.com/questions/9777117/c-char-isnt-converting-to-int) — Scott Hunter, Feb 05 '16 at 22:05
Are you just trying to convert an ASCII value digit character to its numerical value? — e0k, Feb 05 '16 at 22:07
Yes! ... just convert ASCII to unsigned char ... Im new to C — user836026, Feb 05 '16 at 22:09

e0k · Accepted Answer · 2016-02-05T22:23:11.670

1

To convert my_first_reg[0] the ASCII character to its numeric value:

unsigned char value = my_first_reg[0] - '0';

This works because digits in the ASCII table are sequential:

    '0' = 0x30 = 48
    '1' = 0x31 = 49
    '2' = 0x32 = 50
    '3' = 0x33 = 51
    '4' = 0x34 = 52
    ...
    '9' = 0x39 = 57

The above is for converting one character. If you have a longer string, consider using atoi(), strtol(), sscanf(), or something similar.

edited Feb 05 '16 at 22:23

answered Feb 05 '16 at 22:09

e0k

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This works because C requires the character set, be it ASCII or not, to have sequential digits `'0' ... '9'` characters. – chux - Reinstate Monica Feb 05 '16 at 22:18

Convert string containing decimal digit to unsigned char

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