value() [4/4]

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 &&!std::is_same< value_t, ValueType >::value, int >::type = 0>

ValueType nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::value ( const typename object_t::key_type &  key, const ValueType &  default_value  ) const

inline

access specified object element 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(key);
} catch(out_of_range) {
    return default_value;
}

Note

Unlike at(const typename object_t::key_type&), this function does not throw if the given key key was not found.

Unlike operator[](const typename object_t::key_type& key), this function does not implicitly add an element to the position defined by key. This function is furthermore also applicable to const objects.

Parameters

[in]	key	key of the element to access
[in]	default_value	the value to return if key is not found

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 key
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}

See also

see at(const typename object_t::key_type&) for access by reference with range checking

see operator[](const typename object_t::key_type&) for unchecked access by reference

Since

version 1.0.0

Definition at line 21682 of file json.hpp.

    {
        // at only works for objects
        if (JSON_HEDLEY_LIKELY(is_object()))
        {
            // if key is found, return value and given default value otherwise
            const auto it = find(key);
 
            if (it != end())
            {
                return it->template get<ValueType>();
            }
 
            return default_value;
        }
 
        JSON_THROW(type_error::create(306, "cannot use value() with " + std::string(type_name()), *this));
    }