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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
JSON Library Reference
JSON Decoding and Encoding API
JSON decoder functionality
json_decoder_get_double()
Get the double value from the current or the specified node

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
  - JSON Library Reference
    - JSON Library Overview
      The JSON library, libjson, allows applications to decode and encode JSON data. This is useful for reading and interpreting complex data or transferring data between systems.
    - JSON Decoding and Encoding API
      - JSON decoder functionality
        json_decoder_t
        JSON decoder structure
        json_decoder_cleanup()
        Clean up a JSON decoder instance, freeing any memory allocated for the decoder tree
        json_decoder_create()
        Create a new JSON decoder instance
        json_decoder_destroy()
        Destroy a JSON decoder instance
        json_decoder_dump_tree()
        Dump the tree contents of a JSON decoder
        json_decoder_error_t
        JSON decoder error codes
        json_decoder_free_state()
        Free a previously saved JSON decoder state
        json_decoder_get_bool()
        Get the boolean value from the current or the specified node
        json_decoder_get_data_version()
        Get the current data version for the decoder
        json_decoder_get_double()
        Get the double value from the current or the specified node
        json_decoder_get_encoder()
        Return an encoder instance for adding or updating nodes in the decoder tree
        json_decoder_get_int()
        Get the integer value from the current or the specified node
        json_decoder_get_int_ll()
        Get the long long integer value from the current or the specified node
        json_decoder_get_offset()
        Get the offset of the node's value within the original JSON string
        json_decoder_get_parse_error()
        Get the location and reason for a parse error
        json_decoder_get_state()
        Get the current state of the JSON decoder
        json_decoder_get_status()
        Get the error status of the JSON decoder
        json_decoder_get_string()
        Get the string value from the current or the specified node
        json_decoder_index()
        Get the index of the current node
        json_decoder_is_integer()
        Determine if a node represents an integer value
        json_decoder_length()
        Get the number of elements in the current node
        json_decoder_name()
        Get the name of the current property
        json_decoder_next()
        Move to the next node in the current array or object
        json_decoder_parse_error_t
        JSON decoder parser error codes
        json_decoder_parse_file()
        Parse a file of JSON data
        json_decoder_parse_json_str()
        Parse a string of JSON data
        json_decoder_pop()
        Ascend out of an object or array
        json_decoder_position_index()
        Move to the specified node in the current array or object
        json_decoder_position_property()
        Position the decoder at the specified property
        json_decoder_previous()
        Move to the previous node in the current array or object
        json_decoder_push_array()
        Descend into an array
        json_decoder_push_object()
        Descend into an object
        json_decoder_remove_node()
        Remove a node from the decoder tree
        json_decoder_reset()
        Reset a JSON decoder instance
        json_decoder_set_data_version()
        Set the data version for the decoder
        json_decoder_set_state()
        Set the state of the JSON decoder
        json_decoder_set_status()
        Set the error status of the JSON decoder
        json_decoder_state_t
        JSON decoder state
        json_decoder_type()
        Get the type of the current or specified node
        json_node_type_t
        JSON decoder node types
      - JSON encoder functionality
      - JSON utility functions
  - 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 Software in the Cloud enables developers to use the QNX OS in the Amazon cloud environment.
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.
QNX Hypervisor User's Guide
This User's Guide explains the QNX hypervisor architecture and provides instructions for installing and running a QNX Hypervisor system, changing system components and configuration, and using hypervisor features such as virtual devices (vdevs).
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.

json_decoder_get_double()

QNX SDP8.0JSON Library ReferenceAPIDeveloper

Get the double value from the current or the specified node

Synopsis:

#include <sys/json.h>

json_decoder_error_t json_decoder_get_double(json_decoder_t *decoder,
                                             const char *name,
                                             double *value,
                                             bool optional)

Arguments:

decoder: The JSON decoder instance.
name: The name of the node to return the value for, or NULL to return the value for the current node.
value: A pointer to the double that will be updated with the value.
optional: Indicates if the presence of this node is optional. When returning values for optional nodes, the decoder will not register an error status if the node does not exist.

Library:

libjson

Description:

This function gets the double integer value from the current node or from the node with the given name, if the decoder is currently positioned in an object. If successful, the decoder will advance its position to the next node in the object or array.

Returns:

JSON_DECODER_OK: Success.

JSON_DECODER_BAD_TYPE: The specified node is not a number type.

JSON_DECODER_CONVERSION_FAILED: The specified node is an integer type that cannot be accurately represented in a double.

JSON_DECODER_NOT_FOUND: The specified node does not exist.

Page updated: March 05, 2025