Using scanf for reading an unsigned char

Question

I\'m trying to use this code to read values between 0 to 255 (unsigned char).

#include
int main(void)
{
    unsigned char value;         


        

Answer 1

The %u specifier expects an integer which would cause undefined behavior when reading that into a unsigned char. You will need to use the unsigned char specifier %hhu.

Answer 2

For pre C99 I would consider writing an extra function for this just alone to avoid that segmentation fault due to undefined behaviour of scanf.

Approach:

#include<stdio.h>
int my_scanf_to_uchar(unsigned char *puchar)
{
  int retval;
  unsigned int uiTemp;
  retval = scanf("%u", &uiTemp);
  if (retval == 1)   
  {
    if (uiTemp < 256) {
      *puchar = uiTemp;
    }
    else {
      retval = 0; //maybe better something like EINVAL
    }
  }
  return retval; 
}

Then replace scanf("%u", with my_scanf_to_uchar(

Hope this is not off topic as I still used scanf and not another function like getchar :)

Another approach (without extra function)

if (scanf("%u", &uiTemp) == 1 && uiTemp < 256) { value = uitemp; }
else {/* Do something for conversion error */}