convert string to hex number

MIOS programming (C)
1

Hi all there,

A quite small question: is there a simple way to convert a string into a number? On google I’ve seen plenty of stuff with the atoi function but it doesn’t seem to work with me.

I have a string that looks like this: “0xA3” and want to put that A3 hexadecimal value into a u8 number.

Anyone can help?

Best regards

Baptistou

2

On google I’ve seen plenty of stuff with the atoi function but it doesn’t seem to work with me.

I have a string that looks like this: “0xA3” and want to put that A3 hexadecimal value into a u8 number.

0xA3 is hex, you’ll need and integer string like “163” for atoi() to work for you. But if you are going to do that, you might as well just write a hextoi() function yourself.

Here is a simple conversion that will take a two digit hex string in the format “0xHH” and convert it to an int:

#include <ctype.h>


int hextoi(const char * valstr) {


	char valchr[3];

	strncpy(valchr, &valstr[2], 3);

	valchr[0] = toupper(valchr[0]);

	valchr[1] = toupper(valchr[1]);


	int result = 0;

	int positionValue = 1;


	for (int i = 1; i >= 0; i--) {

		int valc = 0;

		if (isalpha(valchr[i])) {

			valc = (int)valchr[i] - (int)'A' + 10;

		}

		else if (isnumber(valchr[i])) {

			valc = (int)valchr[i] - (int)'0';

		}


		result += (valc * positionValue);

		positionValue = positionValue << 4;

	}


	return result;

}


int main (int argc, char * const argv[]) {


	int result = hextoi("0xa3");


	printf("%d", result);

}

If you want a char value result, it’s easy to convert this function to do that.

3

For STM32/MIOS32 I’m normaly using strtol since it allows to differ between decimal and hexadecimal values.

here an example:

/////////////////////////////////////////////////////////////////////////////
// help function which parses a decimal or hex value
// returns >= 0 if value is valid
// returns -1 if value is invalid
/////////////////////////////////////////////////////////////////////////////
static s32 get_dec(char *word)
{
if( word == NULL )
return -1;

char *next;
long l = strtol(word, &next, 0);

if( word == next )
return -1;

return l; // value is valid
}
[/code]









You have to add "#include \<string.h\>" to the header of your .c file







Best Regards, Thorsten.
4

Thanks guys, I’ve spend the whole day programming yesterday and couldn’t write more smart stuff by the end of the day. This saves me a lot of time!

Baptistou