How to convert char array to byte?

[GolamMostafa]

@lastchancename

atol(), or,if a smaller integer will do, you could use the atoi() function.

atoi() function requires that --
(1) The array containing the elemnets must be char type.
(2) Each elemnt should be an ASCII code for the numberals 0 to 9.
(3) For example: Given the number 255, the array declaration should be:

char myNum = {0x32, 0x35, 0x35, 0x00};
or
char myNum = "255";

The @mirage's following declaration meets Step-(1) only. Therefore, atoi() function will extract 0 (zero) and not the number 255.

char high[4] = "0xff";

[GolamMostafa]

@J-M-L

Would be interesting to know where the "0xFF" string originate from. May be there is more straightforward way if the format could be different. (Otherwise yes, strtoul() is the solution)

Given in Post-1:

char high[] = "0xff";

The strtoul() function correctly extracts the number 255. Would appreciate to heard why the function works when the array contains a non-digit symbol 'x'. As I understand, the parsing should stop at x; as a result, the function should produce 0.

[chrisknightley]

@GolamMostafa

Would appreciate to heard why the function works when the array contains a non-digit symbol 'x'.

The strtol() and strtoul() functions are specially designed to interpret numbers with different radixes.
There are rules for binary, hex and octal notation in C++, and they are implemented so that they can be interpreted.

See strtol() functions documents.
https://www.cplusplus.com/reference/cstdlib/strtol/

[J-M-L]

@GolamMostafa

char myNum = {0x32, 0x35, 0x35, 0x00};

Ooops…

[GolamMostafa]

Thanks for the link.
The strtoul() function is really smart to sense that 0x is the pre-fix for a hexadecimal number and accordingly, it correcltly converts this string: "0xff" into a valid number (255 in decimal and 0xFF in hex).

[J-M-L]

@GolamMostafa

char myNum = "255";

Oooppps

[J-M-L]

@GolamMostafa

The strtoul() function correctly extracts the number 255. Would appreciate to heard why the function works when the array contains a non-digit symbol 'x'. As I understand, the parsing should stop at x; as a result, the function should produce 0.

The function is smart

The doc states

If the base value is between 2 and 36, the format expected for the integral number is a succession of any of the valid digits and/or letters needed to represent integers of the specified radix (starting from '0' and up to 'z' /'Z' for radix 36). The sequence may optionally be preceded by a sign (either + or - ) and, if base is 16, an optional "0x" or "0X" prefix.

[GolamMostafa]

@J-M-L

char myNum = {0x32, 0x35, 0x35, 0x00};
char myNum = "255";

Ooops…

char myNum[] = {0x32, 0x35, 0x35, 0x00};
or
char myNum[] = "255";

[J-M-L]

Better

[GolamMostafa]

@J-M-L

and, if base is 16, an optional "0x" or "0X" prefix.

Noted with thanks.