convert string to hex number

[baptistou]

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

[Narwhal]

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.

[TK.]

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.

[baptistou]

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