Why is the scanf_s function not taking input correctly?

Question

When I input a, the output is not a. Condition is true so why is the output not a?. When I use getchar instead of scanf_s, it works fine. What's the issue?

char op;
scanf_s("%c", &op);
if ( op == 'a' )
    printf("the character is a");
else
    printf("not a");

see [scanf_s](https://msdn.microsoft.com/en-us/library/w40768et.aspx) — BLUEPIXY, Oct 03 '15 at 15:07

score 2 · Answer 1 · edited Oct 03 '15 at 15:13

2

Try scanf() instead of scanf_s().

edited Oct 03 '15 at 15:13

Spikatrix

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answered Oct 03 '15 at 15:05

zulkarnain shah

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VS will emit a warning (maybe an error) when using `scanf()`. This is annoying. – Spikatrix Oct 03 '15 at 15:08
@Cool Guy http://stackoverflow.com/a/23487039/2410359 to quiet warning – chux - Reinstate Monica Oct 03 '15 at 15:18

ameyCU · Answer 2 · 2015-10-03T15:13:21.240

2

Specifier %c (two more such exceptions %s, %[) requires 3rd argument size-

scanf_s("%c", &op, 1);   // 1 to read single character

edited Oct 03 '15 at 15:13

answered Oct 03 '15 at 15:05

ameyCU

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score 0 · Answer 3 · answered Oct 03 '15 at 15:27

The third argument should be sizeof the type. scanf_s is only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdio.h>.

#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>

int main()
{
char op;
scanf_s("%c", &op, sizeof(op));
if ( op == 'a' )
    printf("the character is a");
else
    printf("not a");
    return 0;
}

Why is the scanf_s function not taking input correctly?

3 Answers3