what is the use of fflush stdin in c programming

Question

I have the following program   include  lt stdio h gt   include  lt stdlib h gt   int main        char ans 8       int i      for i 1 i lt  3 i                  printf   n What is the unit of traffic              scanf   s  ans           fflush stdin            if stricmp ans  Earlang    0                        printf   nAnswer is correct                exit 1                     else             if i lt 3              printf   n Try Again  n              printf   n Nunit of traffic is Earlang         What is the use of fflush stdin  in this program

User · Answer

it clears stdin buffer before reading  From the man page      For output streams  fflush   forces a write of all user-space buffered   data for the given output or update stream via the stream s underlying   write function  For input streams  fflush   discards any buffered data   that has been fetched from the underlying file  but has not been   consumed by the application    Note  This is Linux-specific  using fflush   on input streams is undefined by the standard  however  most implementations behave the same as in Linux

User · Answer

It s an unportable way to remove all data from the input buffer till the next newline  I ve seen it used in cases like that   char c  char s 32   puts  Type a char    c getchar    fflush stdin   puts  Type a string    fgets s 32 stdin     Without the fflush    if you type a character  say  a   and the hit enter  the input buffer contains  a n   the getchar   peeks the  a   but the   n  remains in the buffer  so the next fgets   will find it and return an empty string without even waiting for user input   However  note that this use of fflush   is unportable  I ve tested right now on a Linux machine  and it does not work  for example

User · Answer

It s not in standard C  so the behavior is undefined   Some implementation uses it to clear stdin buffer   From C11 7 21 5 2 The fflush function  fflush works only with output update stream  not input stream      If stream points to an output stream or an update stream in which the most recent   operation was not input  the fflush function causes any unwritten data for that stream   to be delivered to the host environment to be written to the file  otherwise  the behavior is   undefined

[c] what is the use of fflush(stdin) in c programming

Examples related to c