// (1) template<class ValueType> ValueType value(const typename object_t::key_type& key, const ValueType& default_value) const; // (2) template<class ValueType> ValueType value(const json_pointer& ptr, const ValueType& default_value) const;
Returns either a copy of an object's element at the specified key key
or a given default value if no element with key key
exists.
The function is basically equivalent to executing
try { return at(key); } catch(out_of_range) { return default_value; }
Returns either a copy of an object's element at the specified JSON pointer ptr
or a given default value if no value at ptr
exists.
The function is basically equivalent to executing
try { return at(ptr); } catch(out_of_range) { return default_value; }
Unlike operator[]
, this function does not implicitly add an element to the position defined by key
/ptr
key. This function is furthermore also applicable to const objects.
ValueType
: type compatible to JSON values, for instance #!cpp int
for JSON integer numbers, #!cpp bool
for JSON booleans, or #!cpp std::vector
types for JSON arrays. Note the type of the expected value at key
/ptr
and the default value default_value
must be compatible.
key
(in) : key of the element to access
default_value
(in) : the value to return if key/ptr found no value
ptr
(in) : a JSON pointer to the element to access
key
or default_value
if key
is not foundptr
or default_value
if no value for ptr
is foundStrong guarantee: if an exception is thrown, there are no changes to any JSON value.
type_error.302
if default_value
does not match the type of the value at key
type_error.306
if the JSON value is not an object; in that case, using value()
with a key makes no sense.type_error.302
if default_value
does not match the type of the value at ptr
type_error.306
if the JSON value is not an object; in that case, using value()
with a key makes no sense.??? example
The example below shows how object elements can be queried with a default value. ```cpp --8<-- "examples/basic_json__value.cpp" ``` Output: ```json --8<-- "examples/basic_json__value.output" ```
??? example
The example below shows how object elements can be queried with a default value. ```cpp --8<-- "examples/basic_json__value_ptr.cpp" ``` Output: ```json --8<-- "examples/basic_json__value_ptr.output" ```