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Top Forums Programming Why does fflush(stdin) fail to work ? Post 303022512 by chihuyu on Sunday 2nd of September 2018 06:34:17 AM
Old 09-02-2018
Why does fflush(stdin) fail to work ?

Code:
   #include <stdio.h>
    #include <stdlib.h>
    int main(void)
    {
        double number;
        while (scanf("%lf", &number) != 1)
        {   
            printf("Error\n");
           
        }   
        printf("%lf\n", number);
    
    
        return 0;
    }

Look at the above code.

I want the program to stop for me to type something again every time scanf gets an invalid value.


Never ending loop occurs.

I know the first invalid value has not been cleared and is still in the buffer.

So I use fflush(stdin).

Code:
    #include <stdio.h>
    #include <stdlib.h>
    int main(void)
    {
        double number;
        while (scanf("%lf", &number) != 1)
        {   
            printf("Error\n");
            fflush(stdin);
        }   
        printf("%lf\n", number);
    
    
        return 0;
    }


However, it keeps failing to work.

Why am I wrong and how can I modify the code to make that work?
 

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scanf(3int)															       scanf(3int)

Name
       scanf, fscanf, sscanf - convert formatted input

Syntax
       #include <stdio.h>

       int scanf( format [, pointer ] ...  )
       char *format;

       int fscanf( stream, format [, pointer ] ...  )
       FILE *stream;
       char *format;

       int sscanf( s, format [, pointer ] ...  )
       char *s, *format;

Description
       The  international functions and are similar to the standard I/O functions. The difference is that the international functions allow you to
       use the %digit$ conversion character in place of the I% character you use in the standard I/O functions. The digit is  a  decimal  digit  n
       from 1 to 9.  The international functions apply conversions to the n th argument in the argument list, rather than to the next unused argu-
       ment.

       You can use % conversion character in the international functions.  However, you cannot mix the % conversion  character	with  the  %digit$
       conversion character in a single call.

       In  all	cases,	uses the radix character and collating sequence that is defined by the last successful call to category or If the radix or
       collating sequence is undefined, the function uses the C locale definitions.

   International Environment
       LC_COLLATE     Contains the user requirements for language, territory, and codeset for the character collation format.  affects the  behav-
		      ior  of regular expressions and the string collation functions in If is not defined in the current environment, provides the
		      necessary default.

       LC_NUMERIC     If this environment is set and valid, uses the international language database named in the definition  to  determine  radix
		      character rules.

       LANG	      If  this environment variable is set and valid uses the international language database named in the definition to determine
		      collation and character classification rules.  If or is defined,	their definitions supersede the definition of LANG.

Examples
       The following shows an example of using the function:
       scanf("%2$s %1$d", integer, string)
       If the input is `` january 9 '', the function assigns 9 to and ``january'' to

Return Values
       The function returns the number of successfully matched and assigned input fields.  This number can be  zero  if  the  function	encounters
       invalid input characters, as specified by the conversion specification, before it can assign input characters.

       If  the	input ends before the first conflict or conversion, returns EOF.  These functions return EOF on end of input and a short count for
       missing or invalid data items.

Environment
       In POSIX mode, the E, F, and X formats are treated the same as the e, f, and x formats, respectively;  otherwise,  the  upper-case  formats
       expect double, double, and long arguments, respectively.

See Also
       intro(3int), setlocale(3), strtod(3), strtol(3), printf(3int), getc(3s), printf(3s), scanf(3s)
       Guide to Developing International Software

																       scanf(3int)
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