STDLIB Console and I/O operations

This section explains the console and the asynchronous input/output operations of STDLIB.

Console versus terminals

The STDLIB console (encapsulated by class CTtyDesc, defined in fdesc.h) is a client of the CConsoleBase class implemented by econs.dll. It provides very simple text input and output with no support for embedded control sequences. When STDLIB receives a character from the console it prints it out to the same console, providing a "local echo" facility to make simple command-line interfaces possible.

STDLIB does not provide any sort of terminal driver or line-discipline. In particular there is no support for local processing of backspace, nor any line buffering. Neither does it provide termio or termcap facilities. The Symbian platform is a graphics-based system and it is recommended that C code be ported into a Symbian program which uses a graphical user interface.

Asynchronous I/O vs blocking I/O

All STDLIB I/O operations are blocking; that is they will suspend the calling thread indefinitely until the I/O completes. Hence, in general, STDLIB I/O must not be used in a Symbian platform active object because it will cause the entire active scheduler to block. A possible way to avoid this problem might be to use fcntl() for individual file descriptors, but STDLIB does not currently implement this function.

Asynchronous I/O can be achieved using a set of C++ functions provided by STDLIB which implement a per-file-descriptor equivalent of the POSIX select() function. These functions provide a form of the ioctl() function which takes a TRequestStatus& as a parameter, together with functions for completing the ioctl() operation once the status has been signaled or canceling the pending ioctl. This scheme can be used within an active object to wait for a socket to become ready for reading or writing, so that the subsequent i/o does not block the whole active scheduler. See estlib.h for the interface to these functions. For more information on active objects and active scheduler, see active objects.

NOTE: There are no such blocking problems with I/O to local files, which is essentially a synchronous operation.

See also

Active Objects