fix for #133
added value() function to get object value at given key or a default value if key does not exist
This commit is contained in:
Niels
parent
2ba901bbf6
commit
cd04a7d3e9
7 changed files with 325 additions and 7 deletions
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@ -395,7 +395,7 @@ $ make
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$ ./json_unit "*"
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===============================================================================
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All tests passed (3341803 assertions in 28 test cases)
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All tests passed (3341846 assertions in 28 test cases)
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```
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For more information, have a look at the file [.travis.yml](https://github.com/nlohmann/json/blob/master/.travis.yml).
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29
doc/examples/basic_json__value.cpp
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29
doc/examples/basic_json__value.cpp
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@ -0,0 +1,29 @@
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#include <json.hpp>
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using namespace nlohmann;
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int main()
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{
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// create a JSON object with different entry types
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json j =
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{
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{"integer", 1},
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{"floating", 42.23},
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{"string", "hello world"},
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{"boolean", true},
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{"object", {{"key1", 1}, {"key2", 2}}},
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{"array", {1, 2, 3}}
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};
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// access existing values
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int v_integer = j.value("integer", 0);
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double v_floating = j.value("floating", 47.11);
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// access nonexisting values and rely on default value
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std::string v_string = j.value("nonexisting", "oops");
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bool v_boolean = j.value("nonexisting", false);
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// output values
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std::cout << std::boolalpha << v_integer << " " << v_floating
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<< " " << v_string << " " << v_boolean << "\n";
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}
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1
doc/examples/basic_json__value.link
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1
doc/examples/basic_json__value.link
Normal file
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@ -0,0 +1 @@
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<a target="_blank" href="http://melpon.org/wandbox/permlink/pehnjdIduvv90qfX"><b>online</b></a>
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1
doc/examples/basic_json__value.output
Normal file
1
doc/examples/basic_json__value.output
Normal file
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@ -0,0 +1 @@
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1 42.23 oops false
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102
src/json.hpp
102
src/json.hpp
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@ -2514,6 +2514,10 @@ class basic_json
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@liveexample{The example below shows how object elements can be read and
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written using at.,at__object_t_key_type}
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@sa @ref operator[](const typename object_t::key_type&) for unchecked
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access by reference
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@sa @ref value() for access by value with a default value
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*/
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reference at(const typename object_t::key_type& key)
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{
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@ -2546,6 +2550,10 @@ class basic_json
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@liveexample{The example below shows how object elements can be read using
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at.,at__object_t_key_type_const}
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@sa @ref operator[](const typename object_t::key_type&) for unchecked
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access by reference
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@sa @ref value() for access by value with a default value
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*/
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const_reference at(const typename object_t::key_type& key) const
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{
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@ -2655,6 +2663,10 @@ class basic_json
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@liveexample{The example below shows how object elements can be read and
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written using the [] operator.,operatorarray__key_type}
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@sa @ref at(const typename object_t::key_type&) for access by reference
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with range checking
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@sa @ref value() for access by value with a default value
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*/
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reference operator[](const typename object_t::key_type& key)
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{
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@ -2697,6 +2709,10 @@ class basic_json
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@liveexample{The example below shows how object elements can be read and
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written using the [] operator.,operatorarray__key_type}
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@sa @ref at(const typename object_t::key_type&) for access by reference
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with range checking
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@sa @ref value() for access by value with a default value
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*/
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template<typename T, std::size_t n>
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reference operator[](const T (&key)[n])
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@ -2719,6 +2735,86 @@ class basic_json
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}
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}
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/*!
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@brief access specified object element with default value
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Returns either a copy of an object's element at the specified key @a key or
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a given default value if no element with key @a key exists.
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The function is basically equivalent to executing
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@code{.cpp}
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try {
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return at(key);
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} catch(std::out_of_range) {
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return default_value;
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}
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@endcode
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@note Unlike @ref at(const typename object_t::key_type&), this function
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does not throw if the given key @a key was not found.
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@note Unlike @ref operator[](const typename object_t::key_type& key), this
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function does not implicitly add an element to the position defined by @a
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key. This function is furthermore also applicable to const objects.
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@param[in] key key of the element to access
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@param[in] default_value the value to return if @a key is not found
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@tparam ValueType type compatible to JSON values, for instance `int` for
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JSON integer numbers, `bool` for JSON booleans, or `std::vector` types for
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JSON arrays. Note the type of the expected value at @a key and the default
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value @a default_value must be compatible.
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@return copy of the element at key @a key or @a default_value if @a key
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is not found
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@throw std::domain_error if JSON is not an object
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@complexity Logarithmic in the size of the container.
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@liveexample{The example below shows how object elements can be queried
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with a default value.,basic_json__value}
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@sa @ref at(const typename object_t::key_type&) for access by reference
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with range checking
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@sa @ref operator[](const typename object_t::key_type&) for unchecked
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access by reference
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*/
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template <class ValueType, typename
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std::enable_if<
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std::is_convertible<basic_json_t, ValueType>::value
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, int>::type = 0>
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ValueType value(const typename object_t::key_type& key, ValueType default_value) const
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{
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// at only works for objects
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if (is_object())
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{
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// if key is found, return value and given default value otherwise
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const auto it = find(key);
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if (it != end())
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{
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return *it;
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}
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else
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{
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return default_value;
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}
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}
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else
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{
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throw std::domain_error("cannot use value() with " + type_name());
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}
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}
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/*!
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// overload for a default value of type const char*
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@copydoc basic_json::value()
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*/
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string_t value(const typename object_t::key_type& key, const char* default_value) const
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{
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return value(key, string_t(default_value));
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}
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/*!
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@brief access the first element
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@ -5660,9 +5756,9 @@ class basic_json
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/*!
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@brief wrapper to access iterator member functions in range-based for
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This class allows to access @ref key() and @ref value() during range-based
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for loops. In these loops, a reference to the JSON values is returned, so
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there is no access to the underlying iterator.
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This class allows to access @ref iterator::key() and @ref iterator::value()
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during range-based for loops. In these loops, a reference to the JSON
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values is returned, so there is no access to the underlying iterator.
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*/
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class iterator_wrapper
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{
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@ -2514,6 +2514,10 @@ class basic_json
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@liveexample{The example below shows how object elements can be read and
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written using at.,at__object_t_key_type}
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@sa @ref operator[](const typename object_t::key_type&) for unchecked
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access by reference
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@sa @ref value() for access by value with a default value
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*/
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reference at(const typename object_t::key_type& key)
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{
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@ -2546,6 +2550,10 @@ class basic_json
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@liveexample{The example below shows how object elements can be read using
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at.,at__object_t_key_type_const}
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@sa @ref operator[](const typename object_t::key_type&) for unchecked
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access by reference
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@sa @ref value() for access by value with a default value
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*/
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const_reference at(const typename object_t::key_type& key) const
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{
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@ -2655,6 +2663,10 @@ class basic_json
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@liveexample{The example below shows how object elements can be read and
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written using the [] operator.,operatorarray__key_type}
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@sa @ref at(const typename object_t::key_type&) for access by reference
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with range checking
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@sa @ref value() for access by value with a default value
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*/
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reference operator[](const typename object_t::key_type& key)
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{
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@ -2697,6 +2709,10 @@ class basic_json
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@liveexample{The example below shows how object elements can be read and
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written using the [] operator.,operatorarray__key_type}
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@sa @ref at(const typename object_t::key_type&) for access by reference
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with range checking
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@sa @ref value() for access by value with a default value
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*/
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template<typename T, std::size_t n>
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reference operator[](const T (&key)[n])
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@ -2719,6 +2735,86 @@ class basic_json
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}
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}
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/*!
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@brief access specified object element with default value
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Returns either a copy of an object's element at the specified key @a key or
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a given default value if no element with key @a key exists.
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The function is basically equivalent to executing
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@code{.cpp}
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try {
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return at(key);
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} catch(std::out_of_range) {
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return default_value;
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}
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@endcode
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@note Unlike @ref at(const typename object_t::key_type&), this function
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does not throw if the given key @a key was not found.
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@note Unlike @ref operator[](const typename object_t::key_type& key), this
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function does not implicitly add an element to the position defined by @a
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key. This function is furthermore also applicable to const objects.
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@param[in] key key of the element to access
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@param[in] default_value the value to return if @a key is not found
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@tparam ValueType type compatible to JSON values, for instance `int` for
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JSON integer numbers, `bool` for JSON booleans, or `std::vector` types for
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JSON arrays. Note the type of the expected value at @a key and the default
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value @a default_value must be compatible.
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@return copy of the element at key @a key or @a default_value if @a key
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is not found
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@throw std::domain_error if JSON is not an object
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@complexity Logarithmic in the size of the container.
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@liveexample{The example below shows how object elements can be queried
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with a default value.,basic_json__value}
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@sa @ref at(const typename object_t::key_type&) for access by reference
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with range checking
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@sa @ref operator[](const typename object_t::key_type&) for unchecked
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access by reference
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*/
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template <class ValueType, typename
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std::enable_if<
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std::is_convertible<basic_json_t, ValueType>::value
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, int>::type = 0>
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ValueType value(const typename object_t::key_type& key, ValueType default_value) const
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{
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// at only works for objects
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if (is_object())
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{
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// if key is found, return value and given default value otherwise
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const auto it = find(key);
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if (it != end())
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{
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return *it;
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}
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else
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{
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return default_value;
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}
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}
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else
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{
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throw std::domain_error("cannot use value() with " + type_name());
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}
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}
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/*!
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// overload for a default value of type const char*
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@copydoc basic_json::value()
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*/
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string_t value(const typename object_t::key_type& key, const char* default_value) const
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{
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return value(key, string_t(default_value));
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}
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/*!
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@brief access the first element
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@ -5660,9 +5756,9 @@ class basic_json
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/*!
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@brief wrapper to access iterator member functions in range-based for
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This class allows to access @ref key() and @ref value() during range-based
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for loops. In these loops, a reference to the JSON values is returned, so
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there is no access to the underlying iterator.
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This class allows to access @ref iterator::key() and @ref iterator::value()
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during range-based for loops. In these loops, a reference to the JSON
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values is returned, so there is no access to the underlying iterator.
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*/
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class iterator_wrapper
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{
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@ -3082,6 +3082,101 @@ TEST_CASE("element access")
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}
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}
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SECTION("access specified element with default value")
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{
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SECTION("access existing value")
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{
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CHECK(j.value("integer", 2) == 1);
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CHECK(j.value("integer", 1.0) == Approx(1));
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CHECK(j.value("null", json(1)) == json());
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CHECK(j.value("boolean", false) == true);
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CHECK(j.value("string", "bar") == "hello world");
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CHECK(j.value("string", std::string("bar")) == "hello world");
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CHECK(j.value("floating", 12.34) == Approx(42.23));
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CHECK(j.value("floating", 12) == 42);
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CHECK(j.value("object", json({{"foo", "bar"}})) == json(json::object()));
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CHECK(j.value("array", json({10, 100})) == json({1, 2, 3}));
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CHECK(j_const.value("integer", 2) == 1);
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CHECK(j_const.value("integer", 1.0) == Approx(1));
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CHECK(j_const.value("boolean", false) == true);
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CHECK(j_const.value("string", "bar") == "hello world");
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CHECK(j_const.value("string", std::string("bar")) == "hello world");
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CHECK(j_const.value("floating", 12.34) == Approx(42.23));
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CHECK(j_const.value("floating", 12) == 42);
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CHECK(j_const.value("object", json({{"foo", "bar"}})) == json(json::object()));
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CHECK(j_const.value("array", json({10, 100})) == json({1, 2, 3}));
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}
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SECTION("access non-existing value")
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{
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CHECK(j.value("_", 2) == 2);
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CHECK(j.value("_", false) == false);
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CHECK(j.value("_", "bar") == "bar");
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CHECK(j.value("_", 12.34) == Approx(12.34));
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CHECK(j.value("_", json({{"foo", "bar"}})) == json({{"foo", "bar"}}));
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CHECK(j.value("_", json({10, 100})) == json({10, 100}));
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CHECK(j_const.value("_", 2) == 2);
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CHECK(j_const.value("_", false) == false);
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CHECK(j_const.value("_", "bar") == "bar");
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CHECK(j_const.value("_", 12.34) == Approx(12.34));
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CHECK(j_const.value("_", json({{"foo", "bar"}})) == json({{"foo", "bar"}}));
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CHECK(j_const.value("_", json({10, 100})) == json({10, 100}));
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}
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SECTION("access on non-object type")
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{
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SECTION("null")
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{
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json j_nonobject(json::value_t::null);
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const json j_nonobject_const(j_nonobject);
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CHECK_THROWS_AS(j_nonobject.value("foo", 1), std::domain_error);
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CHECK_THROWS_AS(j_nonobject_const.value("foo", 1), std::domain_error);
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}
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SECTION("boolean")
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{
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json j_nonobject(json::value_t::boolean);
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const json j_nonobject_const(j_nonobject);
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CHECK_THROWS_AS(j_nonobject.value("foo", 1), std::domain_error);
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CHECK_THROWS_AS(j_nonobject_const.value("foo", 1), std::domain_error);
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}
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SECTION("string")
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{
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json j_nonobject(json::value_t::string);
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const json j_nonobject_const(j_nonobject);
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CHECK_THROWS_AS(j_nonobject.value("foo", 1), std::domain_error);
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CHECK_THROWS_AS(j_nonobject_const.value("foo", 1), std::domain_error);
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}
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SECTION("array")
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{
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json j_nonobject(json::value_t::array);
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const json j_nonobject_const(j_nonobject);
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CHECK_THROWS_AS(j_nonobject.value("foo", 1), std::domain_error);
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CHECK_THROWS_AS(j_nonobject_const.value("foo", 1), std::domain_error);
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}
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SECTION("number (integer)")
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{
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json j_nonobject(json::value_t::number_integer);
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const json j_nonobject_const(j_nonobject);
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CHECK_THROWS_AS(j_nonobject.value("foo", 1), std::domain_error);
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CHECK_THROWS_AS(j_nonobject_const.value("foo", 1), std::domain_error);
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}
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SECTION("number (floating-point)")
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{
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json j_nonobject(json::value_t::number_float);
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const json j_nonobject_const(j_nonobject);
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CHECK_THROWS_AS(j_nonobject.value("foo", 1), std::domain_error);
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CHECK_THROWS_AS(j_nonobject_const.value("foo", 1), std::domain_error);
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}
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}
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}
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SECTION("front and back")
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{
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// "array" is the smallest key
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