value() [2/4]

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer, class BinaryType = std::vector<std::uint8_t>>

template<class ValueType , typename std::enable_if< detail::is_getable< basic_json_t, ValueType >::value, int >::type = 0>

ValueType nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::value ( const json_pointer &  ptr, const ValueType &  default_value  ) const

inline

access specified object element via JSON Pointer with default value

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(ptr);
} catch(out_of_range) {
    return default_value;
}

Note

Unlike at(const json_pointer&), this function does not throw if the given key key was not found.

Parameters

[in]	ptr	a JSON pointer to the element to access
[in]	default_value	the value to return if ptr found no value

Template Parameters

ValueType

type compatible to JSON values, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.

Returns

copy of the element at key key or default_value if key is not found

Exceptions

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.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value_ptr}

See also

see operator[](const json_pointer&) for unchecked access by reference

Since

version 2.0.2

Definition at line 21755 of file json.hpp.

    {
        // at only works for objects
        if (JSON_HEDLEY_LIKELY(is_object()))
        {
            // if pointer resolves a value, return it or use default value
            JSON_TRY
            {
                return ptr.get_checked(this).template get<ValueType>();
            }
            JSON_INTERNAL_CATCH (out_of_range &)
            {
                return default_value;
            }
        }
 
        JSON_THROW(type_error::create(306, "cannot use value() with " + std::string(type_name()), *this));
    }