Re: wip/mu: std::getline returning falsy value

[Martin Husemann <martin%duskware.de@localhost>]

On Thu, Apr 18, 2024 at 01:24:39PM +0000, Kevin Bloom wrote:
> > This would happen e.g. if the stdin of the program has been closed.
> 
> Do you have any ideas of what would cause such a thing to happen? I'm
> assuming it shouldn't happening since it's in the standard library...

No, I mean it would probably happen outside of the standard library.
Below is an example that demonstrates it, it's output looks like:

--8<--
 > ./a.out
hi there
the line you entered: hi there
something bad happened to std::cin!
-->8--

So the first std::getline() call works fine, but then the fclose(stdin)
makes the second call fail.

Martin


#include <string>
#include <iostream>

int main(int argc, char **argv)
{
	std::string aLine;

	std::getline(std::cin, aLine);
	std::cout << "the line you entered: " << aLine << std::endl;

	fclose(stdin);

	std::getline(std::cin, aLine);
	if (!std::cin) {
		std::cout << "something bad happened to std::cin!" << std::endl;
		return 1;
	}
	std::cout << "the line you entered: " << aLine << std::endl;

	return 0;
}