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.
	WrappedJsonValue (JsonType js)
	By default the error mode is error::is_throw.
	WrappedJsonValue (JsonType js, error mode)
	Construct with Json value and error mode.
void	set_mode (error new_mode)
	Change the error mode.
const JsonType &	asJson () const
	Read access to the raw Json value.
JsonType &	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.
std::string	toStyledString () const
	The stored json object as a formatted string.
bool	isMember (std::string key) const
	Return true if key is a Member of the json value.
WrappedJsonValue	operator[] (std::string key) const
WrappedJsonValue	get (std::string key, const JsonType &value) const
	Wrap the corresponding JsonType function with error handling.
WrappedJsonValue	operator[] (unsigned idx) const
	Wrap the corresponding JsonType function with error handling.
WrappedJsonValue	get (unsigned idx, const JsonType &value) const
	Wrap the corresponding JsonType function with error handling.
unsigned	size () const
	Wrap the corresponding JsonType function with error handling.
double	asDouble (double value=0) const
	Wrap the corresponding JsonType function with error handling.
unsigned	asUInt (unsigned value=0) const
	Wrap the corresponding JsonType function with error handling.
int	asInt (int value=0) const
	Wrap the corresponding JsonType function with error handling.
bool	asBool (bool value=false) const
	Wrap the corresponding JsonType function with error handling.
std::string	asString (std::string value="") const
	Wrap the corresponding JsonType function with error handling.

Detailed Description

Wrapped Access to Json values with error handling.

The purpose of this class is to serve as an extremely pedantic access guard to a Json file, in the sense that it will raise exceptions at the slightest misstep, for example when a key is misspelled, missing or has the wrong type. It will then compose an error message that shows where exactly the access in the file went wrong and thus help a user quickly debug the input (file).

This is necessary if the cost of a faulty input file with silly mistakes like misspelling could lead to potentially large (computational) costs if uncaught.

The interface of WrappedJsonValue is modelled after jsoncpp's Json::Value:

auto 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 a std::runtime_error
    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.

The caveat of this class is that once a json value is wrapped it is somewhat awkward to change its value (because it is what the class wants to prevent)

Attention

This class is only for read access. If you must change a value do so on the raw JsonType accesible with the asJson() method

Do not assign to a key like this:

dg::file::WrappedJsonValue ws;
ws["hello"]["world"] = dg::file::file2Json("test.json");
// NOT WHAT YOU EXPECT!
// it just assigns to a copy that goes out of scope
// instead you need to work on the unwrapped json directly
auto js = ws.asJson();
js["hello"]["world"] = dg::file::file2Json("test.json")

Note

If the Marco DG_USE_JSONHPP is defined, the #include <nlohmann/json.hpp> parser is used instead of #include <json/json.h> Since the former is header-only no additional linker options must be present at compilation.

Constructor & Destructor Documentation

WrappedJsonValue() [1/4]

dg::file::WrappedJsonValue::WrappedJsonValue ( )

inline

Default constructor By default the error mode is error::is_throw.

WrappedJsonValue() [2/4]

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

inline

Construct with error mode.

Parameters

mode	The error mode

WrappedJsonValue() [3/4]

dg::file::WrappedJsonValue::WrappedJsonValue ( JsonType js )

inline

By default the error mode is error::is_throw.

Parameters

js	The Json value that will be guarded

WrappedJsonValue() [4/4]

dg::file::WrappedJsonValue::WrappedJsonValue ( JsonType 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

asBool()

bool dg::file::WrappedJsonValue::asBool ( bool value = false ) const

inline

Wrap the corresponding JsonType function with error handling.

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asDouble()

double dg::file::WrappedJsonValue::asDouble ( double value = 0 ) const

inline

Wrap the corresponding JsonType function with error handling.

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asInt()

int dg::file::WrappedJsonValue::asInt ( int value = 0 ) const

inline

Wrap the corresponding JsonType function with error handling.

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asJson() [1/2]

JsonType & dg::file::WrappedJsonValue::asJson ( )

inline

Write access to the raw Json value (if you know what you are doing)

asJson() [2/2]

const JsonType & dg::file::WrappedJsonValue::asJson ( ) const

inline

Read access to the raw Json value.

asString()

std::string dg::file::WrappedJsonValue::asString ( std::string value = "" ) const

inline

Wrap the corresponding JsonType function with error handling.

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asUInt()

unsigned dg::file::WrappedJsonValue::asUInt ( unsigned value = 0 ) const

inline

Wrap the corresponding JsonType function with error handling.

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get() [1/2]

WrappedJsonValue dg::file::WrappedJsonValue::get ( std::string key, const JsonType & value ) const

inline

Wrap the corresponding JsonType function with error handling.

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get() [2/2]

WrappedJsonValue dg::file::WrappedJsonValue::get ( unsigned idx, const JsonType & value ) const

inline

Wrap the corresponding JsonType function with error handling.

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isMember()

bool dg::file::WrappedJsonValue::isMember ( std::string key ) const

inline

Return true if key is a Member of the json value.

operator[]() [1/2]

WrappedJsonValue dg::file::WrappedJsonValue::operator[] ( std::string key ) const

inline

Wrap the corresponding JsonType function with error handling

Attention

Do not assign to this! You will assign to a copy

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operator[]() [2/2]

WrappedJsonValue dg::file::WrappedJsonValue::operator[] ( unsigned idx ) const

inline

Wrap the corresponding JsonType function with error handling.

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set_mode()

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

inline

Change the error mode.

Parameters

new_mode

The new error mode

size()

unsigned dg::file::WrappedJsonValue::size ( ) const

inline

Wrap the corresponding JsonType function with error handling.

toStyledString()

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

inline

The stored json object as a formatted string.

Useful when writing json to file

Returns

A string displaying json object

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

• json_wrapper.h