Re: [LIP] std::cin.readsome(...) and std::cin.rdbuf()->in_avail()

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  >>> On Tuesday 02 December 2003 08:33 pm, JP <Josy P. Pullockara> said:

    JP> When it is undesirable to wait for input from a keyboard to std::cin
 we JP> use either std::cin.readsome() to peek at the stream. Also
    JP> std::cin.in_avail() can be used for similar purposes.
    JP>
    JP> But, how to know in this situation whether std::cin has received
 <EOF> JP> as both the above functions do not set the ios_base::eofbit. JP>
    JP> For example,
    JP>
[snip]
    JP> int main(void)
    JP> {
    JP> 	while (std::cin) {
    JP> 		if (std::cin.rdbuf()->in_avail()) parse(std::cin);
    JP> 		else /* do something */ ;
    JP> 	}
    JP> 	return 0;
    JP> }
    JP> will NOT quit when <ctrl-D> is pressed. It does quit if followed by a
 \n JP> ie., <Enter>. What can be done in main() to quit when <ctrl-D> is JP>
 pressed? Should not std::istream::readsome() and in_avail() set the JP>
 ios_base::eofbit?
    JP>
    JP>

Hi,
 In UNIX, pressing ctrl-D at the start of a line acts as end-of-file. Pressing
it somewhere else within a line in your program doesn't work. (check it out!)
You have to test the stream for EOF if you want to exit with ctrl-d.

The easiest and most common way is to test a stream within a conditional, as
EOF sets the fail flag.

For example, instead of using just :

	while (std::cin){ ....}

declare a string (or whatever data you wanna force from user), eg str, and do

	while (std::cin >> str){.....}

As soon as you press ctrl-d, this conditional fails and your program exits.
Now you have the input stored in a string and you can manipulate it as you
want. The fail flag is set when any stream operation fails, like attempting
to read a name fails due to end of file, or something other than the expected
data type appears in the stream

Your code suggests that you want to manipulate the stream directly. So you wud
probably have to find a workaround if you want to use cin::rdbuf->in_avail()
etc. or else change the code as cin is no longer required. In fact it gets
simpler and shorter this way.

Regards,
Bhaskar.

- --

- ---------------------------
Bhaskar Dutta <[email protected]> <[email protected]>
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