Help! Cin killed Cout ...

[maccatalan]

Hi.

I made a C++ program. It's works very well on Linux and on CodeWarrior's SIOUX-WASTE interface, but not on Darwin's console. I mean :

when I do :
cout << "Enter a key : ";
cin >> akey;

Then on Darwin the application acts as if there was written in the code :

cin >> akey;
cout << "Enter a key : ";

Of course, if I use cerr instead of cout there's no problem, but more rare : even if I make a flush the problem still exists.

I tried to change the shell, the problem continues.

And the problem is the same in both Terminal application and console (when you log as >console).

Have you got an idea ?
Thank you to help me,
Pierre.

PS: I would like to don't put any endl at the end of text output, since I'd like the user to see "Enter a key : _" (where '_' is the cursor).

 

[ladavacm]

That would seem to be a cout tty flush bug, present in gcc or libiostream.

From C on practically any UNIX, fprintf is autoflushing if you are writing to a tty; it is block-flushing otherwise. To deal with that, one uses:

fprintf( file, format, ... );
fflush( file );

The same should be done using C++:

cout << "whatever";
cout.flush();

This does not seem to work with cout. The FreeBSD 2.95.2 version of gcc always autoflushes cout (wasteful), whereas OS X gcc seems to do that only on endl.

 

[maccatalan]

so without doing :

cerr << "enter a key : ";
cin >> mykey;

there's no solution ...

Thank you anyway,
Pierre.

 

[maccatalan]

you can find more information about this subject on a last thread I didn't see (sorry).

here you've got the <a href="http://www.macosx.com/showthread.php?threadid=4236">link</a>.

Pierre.

 

[bradleysmith]

I'm short on time so look at the code, try it to prove to yourself that it works then read up on the function. Note that IMHO this is not a bug in Mac OS X. I believe the specification for the functions are so wooly that different implementations will work differently. VC++ on windows has a similar problem: -

int foo;
// important bit here!
cin.sync_with_stdio(false);
cout << "Enter a number : ";
cin >> foo;
cout << "you entered " << foo << endl;
return 0;

Note the sync_with-stdio call. This is what makes it all work.

Regards
Brad