getchar() best practices

I have a program that outputs a menu, the input should be a char from stdin. Naturally, I would think to use getchar(). Are you supposed to do the following every time after you are finished getting the character?

Code:

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

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I was googling around and I found fflush(stdin). Unfortunately, the behavior of flushing stdin is undefined, so there goes that idea.

What's the best alternative to using getchar to read character input. Or, do you just have to be prudent to clear stdin of newline characters.

Well if you have say

Code:

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char buff[BUFSIZ];
if ( fgets( buff, sizeof buff, stdin ) != NULL ) {
  // do stuff with buff, say sscanf
}

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Then all the various hacks to clean up the input stream cease to be necessary.

Quote:

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Originally Posted by albundy

I have a program that outputs a menu, the input should be a char from stdin. Naturally, I would think to use getchar(). Are you supposed to do the following every time after you are finished getting the character?

Code:

---

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

---

I was googling around and I found fflush(stdin). Unfortunately, the behavior of flushing stdin is undefined, so there goes that idea.

What's the best alternative to using getchar to read character input. Or, do you just have to be prudent to clear stdin of newline characters.

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It's going to depend what you are reading. Salem has the best suggestion for string inputs, but if you are using the buffer as a string now you need to clean the newline out of the buffer (unless you want your strings to have newlines at the end). For human readable numerics fgets() then sscanf() to pluck your numbers out of the buffer... For single characters getchar() then the little loop you had to clear the \n out of the buffer.

The old standard of fflush(stdin) only works in compilers who's libraries are wired up to clear the input buffer for you (Turbo C, VC++, and a couple of others) but this is non-standard behavior and can't be trusted on other compilers.