Home
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running the QNX OS 8.0.
Utilities & Libraries
Devctl and Ioctl Commands
DCMD_CHR_*
DCMD_CHR_ISCHARS
Determine the number of characters waiting to be read

QNX Momentics IDE User's Guide
This User's Guide describes version 8.0 of the Integrated Development Environment (IDE) that's part of the QNX Tool Suite.
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running the QNX OS 8.0.
- Quickstart Guide
- System Architecture
  The System Architecture guide accompanies the QNX OS and is intended for both application developers and end-users.
- OS Components & Operations
- Graphics
- Programming
- System Security Guide
  The QNX System Security Guide is intended for both system integrators who are responsible for the security of a QNX OS system and developers who want to create a QNX OS resource manager free from vulnerabilities.
- Utilities & Libraries
  - C Library Reference
  - Devctl and Ioctl Commands
    - BIOC*
    - CAN_DEVCTL_*
    - DCMD_ALL_*
    - DCMD_BLK_*
    - DCMD_CHR_*
      - DCMD_CHR_DISABLE_LOGGING
        Disable the logging of transmitted and/or received data
      - DCMD_CHR_ENABLE_LOGGING
        Enable the logging of transmitted and/or received data
      - DCMD_CHR_FLUSH_LOG
        Force a flush of the logged data to the log files
      - DCMD_CHR_FORCE_RTS
        Force the RTS line to the specified level
      - DCMD_CHR_GETOBAND
        Get out-of-band data stored by a device
      - DCMD_CHR_GETOBAND_EXTENDED
        Get extended out-of-band data stored by a device
      - DCMD_CHR_GETSIZE
        Get the size of a character device
      - DCMD_CHR_GETVERBOSITY
        Get the verbosity of io-char
      - DCMD_CHR_IDLE
        Put the device into idle
      - DCMD_CHR_ISATTY
        Test to see if a file descriptor is associated with a terminal
      - DCMD_CHR_ISCHARS
        Determine the number of characters waiting to be read
      - DCMD_CHR_ISSIZE
        Determine the size of the device's input buffer
      - DCMD_CHR_LINESTATUS
        Get line status information for the terminal device
      - DCMD_CHR_OSCHARS
        Determine the number of characters waiting to be sent
      - DCMD_CHR_OSSIZE
        Determine the size of the device's output buffer
      - DCMD_CHR_PARCTL
        Control a parallel device
      - DCMD_CHR_PNPTEXT
        Get the text associated with a plug and play device
      - DCMD_CHR_PUTOBAND
        Send out of band data to the device
      - DCMD_CHR_RESET
        Reset the device
      - DCMD_CHR_RESUME
        Make the device resume from idle
      - DCMD_CHR_SERCTL
        Control serial communication lines
      - DCMD_CHR_SET_LOGGING_DIR
        Set the path to the logging directory
      - DCMD_CHR_SETSIZE
        Set the size of a character device
      - DCMD_CHR_SETVERBOSITY
        Set the verbosity of io-char
      - DCMD_CHR_TCDRAIN
        Wait until all output has been transmitted to a device
      - DCMD_CHR_TCFLOW
        Perform a flow-control operation on a data stream
      - DCMD_CHR_TCFLUSH
        Flush the input or output stream
      - DCMD_CHR_TCGETATTR
        Get the terminal properties
      - DCMD_CHR_TCGETPGRP
        Get the process group ID associated with a device
      - DCMD_CHR_TCGETSID
        Get the process group ID of a controlling terminal's session leader
      - DCMD_CHR_TCINJECTC, DCMD_CHR_TCINJECTR
        Inject characters into a device's input buffer
      - DCMD_CHR_TCSETATTR, DCMD_CHR_TCSETATTRD, DCMD_CHR_TCSETATTRF
        Set terminal properties
      - DCMD_CHR_TCSETPGRP
        Set the process group ID associated with a device
      - DCMD_CHR_TCSETSID
        Set the process group ID of a controlling terminal's session leader
      - DCMD_CHR_TTYINFO
        Get information about a terminal device
      - DCMD_CHR_WAITINFO
        Get information about blocked processes
    - DCMD_DUMPER_*
    - DCMD_F3S_*
    - DCMD_FSYS_*
    - DCMD_IP_*
    - DCMD_MEMMGR_*
    - DCMD_MISC_*
    - DCMD_MMCSD_*
    - DCMD_PROC_*
    - DCMD_PROF_*
    - DCMD_PTPD_*
    - DCMD_SDIO_*
    - DCMD_SDMMC_*
    - DCMD_SPI_*
    - PTP_*
    - FIO*
    - TC*
    - TIOC*
  - JSON Library Reference
  - PAM Reference
  - QNX Helpers Developer's Guide
    These libraries provide QNX helpers, including helpers that assist with logging, string conversion, and number and type sizes.
  - SPI Framework Technote
  - Utilities Reference
  - WPA Control Interface Reference
    This document provides a reference for the Wi-Fi Protected Access (WPA) control interface, which provides a C API for the WPA/IEEE 802.11i protocols in Wi-Fi client stations. Application developers who want to control WPA operations and get associated status and event data should read this reference.
- Migrating to QNX OS 8.0
QNX Software in the Cloud
QNX Toolkit for Visual Studio Code
This User's Guide describes the QNX^® Toolkit for Visual Studio Code. The guide introduces you to the QNX Toolkit by explaining the QNX development environment and how to build, run, and debug your QNX^® Operating System (OS) applications and systems.
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation, explains how to obtain technical support, and provides some information about licensing.

DCMD_CHR_ISCHARS

QNX SDP8.0Devctl and Ioctl CommandsDeveloper

Determine the number of characters waiting to be read

Synopsis:

#include <sys/dcmd_chr.h>

#define DCMD_CHR_ISCHARS    __DIOF('f', 127, unsigned)   /* FIONREAD */

Arguments to devctl():


Argument	Value
`filedes`	A file descriptor that you obtained by opening the device.
`dcmd`	DCMD_CHR_ISCHARS
`dev_data_ptr`	A pointer to an unsigned
`n_bytes`	`sizeof(unsigned)`
`dev_info_ptr`	NULL

Description:

This command determine the number of characters waiting to be read. It's also implemented as the FIONREAD ioctl() command.

Note:

This command is for internal use, and you shouldn't use it directly. Instead use the tcischars() cover function.

Input:

None.

Output:

The number of characters.