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nlohmann
144 lines
4.0 KiB
Markdown
144 lines
4.0 KiB
Markdown
# nlohmann::basic_json::operator!=
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```
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// until C++20
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bool operator!=(const_reference lhs, const_reference rhs) noexcept; // (1)
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template<typename ScalarType>
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bool operator!=(const_reference lhs, const ScalarType rhs) noexcept; // (2)
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template<typename ScalarType>
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bool operator!=(ScalarType lhs, const const_reference rhs) noexcept; // (2)
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// since C++20
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class basic_json {
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bool operator!=(const_reference rhs) const noexcept; // (1)
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template<typename ScalarType>
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bool operator!=(ScalarType rhs) const noexcept; // (2)
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};
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```
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1. Compares two JSON values for inequality. Returns `!(lhs == rhs)` (until C++20) or `!(*this == rhs)` (since C++20).
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- This means the comparison is simply the logical negation of `operator==`, including for special values like `NaN` and `discarded`.
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1. Compares a JSON value and a scalar or a scalar and a JSON value for inequality by converting the scalar to a JSON value and comparing both JSON values according to 1.
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## Template parameters
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`ScalarType` : a scalar type according to `std::is_scalar<ScalarType>::value`
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## Parameters
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`lhs` (in) : first value to consider
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`rhs` (in) : second value to consider
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## Return value
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whether the values `lhs`/`*this` and `rhs` are not equal
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## Exception safety
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No-throw guarantee: this function never throws exceptions.
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## Complexity
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Linear.
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## Notes
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Comparing `NaN` and `discarded`
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Since `operator!=` is defined as `!(a == b)`, the behavior for special values follows that of `operator==`:
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- For `NaN` values: `NaN == NaN` yields `false`, so `NaN != NaN` yields `true`.
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- For `discarded` values: `discarded == x` yields `false` for any `x`, so `discarded != x` yields `true`.
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## Examples
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Example
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The example demonstrates comparing several JSON types.
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create several JSON values
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json array_1 = {1, 2, 3};
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json array_2 = {1, 2, 4};
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json object_1 = {{"A", "a"}, {"B", "b"}};
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json object_2 = {{"B", "b"}, {"A", "a"}};
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json number_1 = 17;
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json number_2 = 17.000000000000001L;
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json string_1 = "foo";
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json string_2 = "bar";
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// output values and comparisons
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std::cout << std::boolalpha;
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std::cout << array_1 << " != " << array_2 << " " << (array_1 != array_2) << '\n';
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std::cout << object_1 << " != " << object_2 << " " << (object_1 != object_2) << '\n';
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std::cout << number_1 << " != " << number_2 << " " << (number_1 != number_2) << '\n';
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std::cout << string_1 << " != " << string_2 << " " << (string_1 != string_2) << '\n';
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}
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```
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Output:
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```
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[1,2,3] != [1,2,4] true
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{"A":"a","B":"b"} != {"A":"a","B":"b"} false
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17 != 17.0 false
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"foo" != "bar" true
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```
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Example
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The example demonstrates comparing several JSON types against the null pointer (JSON `null`).
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create several JSON values
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json array = {1, 2, 3};
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json object = {{"A", "a"}, {"B", "b"}};
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json number = 17;
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json string = "foo";
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json null;
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// output values and comparisons
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std::cout << std::boolalpha;
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std::cout << array << " != nullptr " << (array != nullptr) << '\n';
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std::cout << object << " != nullptr " << (object != nullptr) << '\n';
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std::cout << number << " != nullptr " << (number != nullptr) << '\n';
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std::cout << string << " != nullptr " << (string != nullptr) << '\n';
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std::cout << null << " != nullptr " << (null != nullptr) << '\n';
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}
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```
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Output:
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```
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[1,2,3] != nullptr true
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{"A":"a","B":"b"} != nullptr true
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17 != nullptr true
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"foo" != nullptr true
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null != nullptr false
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```
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## Version history
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1. Added in version 1.0.0. Added C++20 member functions in version 3.11.0. Changed in version 3.13.0 to remove special-casing for `NaN` and `discarded` values; `operator!=` now consistently means `!(a == b)`.
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1. Added in version 1.0.0. Added C++20 member functions in version 3.11.0. Changed in version 3.13.0 to remove special-casing for `NaN` and `discarded` values; `operator!=` now consistently means `!(a == b)`.
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