Question

Are there any dangers to using %*c in scanf() to clear the buffer when necessary.

For example:

char c;
for (int i = 0; i < 5; i++) {
  scanf("%c%*c", &c);
}

Or

char* str;
char c;
int i;
scanf("%s", str);
scanf("%d%*c", &i);
scanf("%c%*c", &c);

Should there be any concern for buffer overflows or other security issues?
There seems to be no formal documentation for the usage of the asterisk in scanf this way for C (EDIT This is not true), so I’m having trouble finding out exactly what happens to the extra characters that are inputted.
Is there a better way of clearing the scanf buffer in C?

Answer 1

You’ll have better luck conceptualizing the task you’re trying to accomplish as “how do I read and discard any junk that the user might’ve typed after what I care about”, which will lead you to constructs such as

int c;
while ((c = getchar()) != EOF && c != '\n') ;  /* discard till end of line or EOF */

But also, you can avoid the entire problem by not using scanf in the first place, which is a good idea for several other reasons. Read entire lines with getline, if you have it, or fgets if you don’t, and parse them by hand.