Alternate method for clearing input buffer in c

Question

Is there any other method to clear the input buffer in c withut using

 fflush();

or

 while(getchar()!='\n');

Because i have read it everywhere and cant find any other way to do it.

@barakmanos sorry sir, but din't you mean while (scanf("%c",&c) == 1);? — Sourav Ghosh
– Sourav Ghosh, Commented Dec 3, 2014 at 13:47
rewind(stdin); and fseek(stdin,0,SEEK_END); might work although i've not tested it... — Spikatrix
– Spikatrix, Commented Dec 3, 2014 at 13:47
What is the use-case where you need something other than this? — Gopi
– Gopi, Commented Dec 3, 2014 at 13:53
@JonatanGoebel , Using fflush on stdin is Undefined Behaviour — Spikatrix
– Spikatrix, Commented Dec 3, 2014 at 14:28

unwind · Accepted Answer · 2014-12-03 13:59:20Z

2

The best solution is to not depend on the input buffer's state so much.

Read input as whole lines, using fgets(), then parse those. Don't use e.g. scanf() to read individual values, since it interacts with the buffer in annoying ways.

answered Dec 3, 2014 at 13:59

unwind

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1 Comment

rahul tyagi Over a year ago

But i m talking about the case eg when using getchar( ) some "/n " or other characters which have not been read interferes with the functioning .using fgets() or getline() is another issue thanks for the reply though .

Community · Accepted Answer · 2017-05-23 12:17:50Z

Using fgets() as suggester @unwind best approach.

To flush to the end of the line.

void FlushStdin(void) { int ch; while(((ch = getchar()) !='\n') && (ch != EOF)); }

If stdin is all ready flushed to the end-of-line, calling FlushStdin() or other posted scanf(), fgetc() solutions, will flush to the end of the next line.

Note scanf("%*[^\n]%*1[\n]"); does not work if the next char is '\n'.

Spikatrix · Accepted Answer · 2023-05-09 04:19:30Z

2

Another method to clear the input buffer (stdin) would be to use

scanf("%*[^\n]"); scanf("%*c");

%*[^\n] instructs scanf to scan everything until a new-line character(\n) and then discards it. The %*c tells scanf to scan and discard a single character which in this case will be the newline character.

edited May 9, 2023 at 4:19

answered Dec 3, 2014 at 14:16

Spikatrix

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4 Comments

David C. Rankin Over a year ago

flushstdin.c:9:5: warning: unknown conversion type character ‘*’ in format [-Wformat=]

chux Over a year ago

"Here, %*[^\n] instructs scanf to scan everything until a new-line character(\n) is found and then discard it." is not true if the first char is '\n'. '\n' remains in stdin.

chux Over a year ago

Using %*c instead of %*1[\n] does not solve the problem when input is only '\n' as that 2nd part of the format specifier is not reached. Instead code code code use 2 independent scanf() calls: scanf("%*[^\n]"); scanf("%*1[\n]"); or scanf("%*[^\n]"); getchar();.

Spikatrix Over a year ago

@chux ,Isn't the % at the end of scanf("%*[^\n]%"); a typo? Anyway,Thanks for making me understand!

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