fpurge()

[jrothwell97]

Right, I'm attempting to flush stdin in a C++ app (because otherwise the menu in my program behaves oddly - it uses getchar().)

On attempting to do an fpurge(stdin), I found that it wasn't declared. I searched the 'net, and found this thread (http://ubuntuforums.org/showthread.php?t=1051954&highlight=fpurge()) which points out that fpurge() is non-standard C and that fflush() doesn't work on GNU/Linux.

All I'm looking for here is a simple answer: how do I flush/purge stdin when compiling on Ubuntu using g++?

[dwhitney67]

The getchar() problem surfaces again... but why in a C++ app?

When reading in a single char, the last char you typed (a newline) is still in the buffer. If you are programming in C++, then is buffer is within std::cin. To clear out the buffer, use something similar to the following:


char ch;
std::cout << "Choice: ";
std::cin >> ch;
std::cin.ignore(128, '\n'); // ignore the next 128 characters


Or you can choose to use one of these choices:

1. use ncurses library;
2. create your own getc() function that manipulates the terminal settings so that the terminal does not block when reading input;
3. read in a string in lieu of a single character

Here's an example for option 3:



#include <string>
#include <iostream>

int main()
{
std::cout << "Menu:\n"
<< "\n\t1. option one"
<< "\n\t2. option two"
<< "\n\t3. option three"
<< "\n\tq. quit"
<< "\n\n"
<< "Enter a choice: ";

std::string choice;

getline(std::cin, choice);

switch (choice[0])
{
case '1': ...
case '2': ...
...
case 'q': ...
}
}

[nvteighen]

The getchar() problem surfaces again... but why in a C++ app?


And again I feel ncurses is the best you can use, as it is designed to be a higher level solution to getchar() and such... Though, I don't know how well does ncurses play in C++.

[dwhitney67]

And again I feel ncurses is the best you can use, as it is designed to be a higher level solution to getchar() and such... Though, I don't know how well does ncurses play in C++.
ncurses works well with C++... I have experience using it back in '97 to develop a simple spreadsheet application when I was taking a course at a community college.

Personally, though, if all that is needed is the ability to get one lousy character, and to discard the trailing newline char, I would not bother with ncurses. It's too much baggage, and the std::cin approach is probably best (whether reading a single-char and ignoring the rest, or reading a string).

[jrothwell97]

Thanks for the help.

std::cin.ignore worked excellently. Note to self: learn C++ properly instead of hotchpotching between it and pure C...