scanf("%*[^\n]"); usage in a c programm?

Question

I have an assignment where i need to find out what scanf("%*[^\n]"); does in a c program. I know that [^\n] means that the input is read until \n and that %* puts the input in the buffer and discards it. I don't understand what usage you can get out of it, because in my understanding it just reads the input till \n and discards it then.

Does this help: https://stackoverflow.com/questions/40038538/how-does-scanf-n-str-work-in-c-programming ? — Adrian Mole, Dec 03 '19 at 12:24
`"%*[^\n]"` can be used to clear the input stream until newline. Where `%*` is to ignore whatever read. — kiran Biradar, Dec 03 '19 at 12:26
"in my understanding it just reads the input till \n and discards it then." And why couldn't that be a useful thing to do ? — Sander De Dycker, Dec 03 '19 at 12:27
@JL2210 it's not the same question. There is a * here, not in the question you referenced. — chmike, Dec 03 '19 at 12:47
@chmike It's the same thing, the `*` only discards the input. — S.S. Anne, Dec 03 '19 at 12:55
@JL2210 : the question here is not so much *how* it works, but rather *why* you would use it. — Sander De Dycker, Dec 03 '19 at 13:16

chux - Reinstate Monica · Answer 1 · 2019-12-03T13:59:56.543

scanf(“%*[^\n]”); usage in a c programm?

It is somewhat common to see yet fgets() is a better approach. Recommend to not use scanf() until you know why you should not use it. Then use it in a limited way.

I don't understand what usage you can get out of it

Example usage: code attempts to read numeric text with scanf("%d", &x); but "abc\n" is in stdin so function returns 0 and data in stdin remains. scanf("%*[^\n]"); clears out (reads and discards) the "abc" in preparation for a new line of input.

int x;
int count;
do {
  puts("Enter number");
  count = scanf("%d", &x);  // count is 0, 1 or EOF
  if (count == 0) {
    scanf("%*[^\n]");   // Read and discard input up, but not including, a \n
    scanf("%*1[\n]");   // Read and discard one \n
  }
} while (count == 0);

if (count == EOF) puts("No more input");
else puts("Success");

Variations like scanf(" %*[^\n]"); and scanf("%*[^\n]%*c"); have their own corner problems (1st consume all leading white-space, even multiple lines, 2nd fails to read anything if the next character is '\n').

scanf("%*[^\n]"); usage in a c programm?

1 Answers1