How to use fflush in c on OS/X

Question

program source codeHow should I use fflush in C on OS/X? When I use it, it does not clear my buffer and terminates the program straight away.

Don't tell me you fflush-ed on `stdin`.... it invokes [undefined behavior](https://en.wikipedia.org/wiki/Undefined_behavior). — Sourav Ghosh, Aug 01 '16 at 11:20
Please show us your code as a [mcve] (or buy us all crystal balls). — kaylum, Aug 01 '16 at 11:39

score 0 · Accepted Answer · answered Aug 01 '16 at 14:28

Calling fflush(stdin); invokes undefined behavior. You should not use this to flush characters from the standard input buffer. Instead, you can read the characters upto the next linefeed and ignore them:

int c;
while ((c = getchar()) != EOF && c != '\n')
    continue;

You can also use scanf() for this, but it is tricky:

scanf("%*^[\n]");  // read and discard any characters different from \n
scanf("%*c");      // read and discard the next char, which, if present, is a \n

Note that you cannot combine the 2 calls above because it would fail to read a linefeed non preceded by any other characters, as the first format would fail.

How to use fflush in c on OS/X

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