dg::file::WrappedJsonValue Struct Reference

Wrapped Access to Json values with error handling. More...

Public Member Functions
	WrappedJsonValue ()
	Default constructor By default the error mode is error::is_throw.
	WrappedJsonValue (error mode)
	Construct with error mode. More...
	WrappedJsonValue (Json::Value js)
	By default the error mode is error::is_throw. More...
	WrappedJsonValue (Json::Value js, error mode)
	Construct with Json value and error mode. More...
void	set_mode (error new_mode)
	Change the error mode. More...
const Json::Value &	asJson () const
	Read access to the raw Json value.
Json::Value &	asJson ()
	Write access to the raw Json value (if you know what you are doing)
std::string	access_string () const
	The creation history of the object. More...
WrappedJsonValue	operator[] (std::string key) const
	Wrap the corresponding Json::Value function with error handling.
WrappedJsonValue	get (std::string key, const Json::Value &value) const
	Wrap the corresponding Json::Value function with error handling.
WrappedJsonValue	operator[] (unsigned idx) const
	Wrap the corresponding Json::Value function with error handling.
WrappedJsonValue	get (unsigned idx, const Json::Value &value) const
	Wrap the corresponding Json::Value function with error handling.
unsigned	size () const
	Wrap the corresponding Json::Value function with error handling.
double	asDouble (double value=0) const
	Wrap the corresponding Json::Value function with error handling.
unsigned	asUInt (unsigned value=0) const
	Wrap the corresponding Json::Value function with error handling.
int	asInt (int value=0) const
	Wrap the corresponding Json::Value function with error handling.
bool	asBool (bool value=false) const
	Wrap the corresponding Json::Value function with error handling.
std::string	asString (std::string value="") const
	Wrap the corresponding Json::Value function with error handling.

Detailed Description

Wrapped Access to Json values with error handling.

The purpose of this class is to wrap the access to a Json::Value with guards that raise exceptions or display warnings in case an error occurs, for example when a key is misspelled, missing or has the wrong type. The goal is the composition of a good error message that helps a user quickly debug the input (file).

The Wrapper is necessary because Jsoncpp by default silently generates a new key in case it is not present which in our scenario is an invitation for stupid mistakes.

You can use the WrappedJsonValue like a Json::Value with read-only access:

Json::Value js;
dg::file::file2Json( "test.json", js);
dg::file::WrappedJsonValue ws( js, dg::file::error::is_throw);
try{
    std::string hello = ws.get( "hello", "").asString();
    // the following access will throw
    int idx0 = ws[ "array" ][out_of_bounds_index].asInt();
} catch ( std::exception& e){
    std::cerr << "Error in file test.json\n";
    //the what string knows that the out of bounds error occured in the array
    //called "array"
    std::cerr << e.what()<<std::endl;
}

A feature of the class is that it keeps track of how a value is called. For example

void some_function( dg::file::WrappedJsonValue ws)
{
    int value = ws[ "some_non_existent_key"].asUInt();
}
 
dg::file::WrappedJsonValue js;
try{
    some_function( js["nested"]);
} catch ( std::exception& e){ std::cerr << e.what()<<std::endl; }
//The what string knows that "some_non_existent_key" is expected to be
//contained in the "nested" key.

Constructor & Destructor Documentation

WrappedJsonValue() [1/3]

dg::file::WrappedJsonValue::WrappedJsonValue ( error  mode )

inline

Construct with error mode.

Parameters

mode	The error mode

WrappedJsonValue() [2/3]

dg::file::WrappedJsonValue::WrappedJsonValue ( Json::Value  js )

inline

By default the error mode is error::is_throw.

Parameters

js	The Json value that will be guarded

WrappedJsonValue() [3/3]

dg::file::WrappedJsonValue::WrappedJsonValue ( Json::Value  js, error  mode  )

inline

Construct with Json value and error mode.

Parameters

js	The Json value that will be guarded
mode	The error mode

Member Function Documentation

access_string()

std::string dg::file::WrappedJsonValue::access_string ( ) const

inline

The creation history of the object.

Useful to print when debugging parameter files

Returns

A string containing object history

set_mode()

void dg::file::WrappedJsonValue::set_mode ( error  new_mode )

inline

Change the error mode.

Parameters

new_mode

The new error mode

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The documentation for this struct was generated from the following file:

• json_utilities.h