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api/basic_json_view/operator_ne.md

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+# <small>nlohmann::basic_json_view::</small>operator!=
+
+```cpp
+// (1)
+bool operator!=(const basic_json_view& lhs, const basic_json_view& rhs);
+
+// (2)
+bool operator!=(const basic_json_view& lhs, const BasicJsonType& rhs);
+bool operator!=(const BasicJsonType& lhs, const basic_json_view& rhs);
+```
+
+1. Compares two views for inequality. Returns `#!cpp !(lhs == rhs)`, see [operator==](operator_eq.md).
+2. Compares a view and a `BasicJsonType` value for inequality, in either order. Returns `#!cpp !(lhs == rhs)` (or,
+   for the reversed order, `#!cpp !(rhs == lhs)`), see [operator==](operator_eq.md).
+
+Since `operator!=` is defined as the negation of [`operator==`](operator_eq.md), it follows the same rules for
+special cases: for instance, since a [discarded](is_discarded.md) view is never equal to anything by default (see
+[operator=='s Notes](operator_eq.md#notes)), it is never *unequal* to anything either -- `#!cpp discarded != discarded`
+is also `#!cpp false`, exactly as for a discarded `BasicJsonType` value.
+
+## Parameters
+
+`lhs` (in)
+:   first value to consider
+
+`rhs` (in)
+:   second value to consider
+
+## Return value
+
+whether the values `lhs` and `rhs` are not equal
+
+## Exception safety
+
+Strong exception safety: if an exception is thrown, there are no changes to either operand, or to the document(s) a
+view refers to.
+
+## Exceptions
+
+May throw `#!cpp std::bad_alloc`, propagated from [`operator==`](operator_eq.md#exceptions). Unlike most other
+`basic_json_view` functions, `operator!=` is not `#!cpp noexcept`.
+
+## Complexity
+
+Linear, as [`operator==`](operator_eq.md#complexity).
+
+## Notes
+
+See the [Notes](operator_eq.md#notes) of `operator==` -- in particular for how an object's members are compared
+(order matters for [`ordered_json_view`](../ordered_json_view.md) but not for [`json_view`](../json_view.md)) and
+for how discarded views compare.
+
+No ordering comparison (`#!cpp operator<`) is provided for `basic_json_view`; [`materialize()`](materialize.md) is
+the way to get a `BasicJsonType` value that supports it.
+
+## Examples
+
+??? example
+
+    The example below asserts, as a test would, that a received document differs from an unwanted value, and shows
+    that -- as for [`json`](../json.md)/[`ordered_json`](../ordered_json.md) -- reordering an object's members is
+    detected as a difference for an `ordered_json_view` but not for a `json_view`.
+
+    ```cpp
+    #include <iostream>
+    #include <nlohmann/json_view.hpp>
+    
+    using json_document = nlohmann::json_document;
+    using ordered_json_document = nlohmann::ordered_json_document;
+    using json = nlohmann::json;
+    
+    int main()
+    {
+        // assert, as a test would, that a received document differs from an
+        // unwanted shape -- without ever materializing it into a json value just
+        // to compare
+        const json_document received = json_document::parse(
+                                           R"({"status": "ok", "code": 200})");
+        const json unwanted = {{"status", "error"}, {"code", 500}};
+        std::cout << std::boolalpha << (received.root() != unwanted) << '\n';
+    
+        // json (std::map) compares object members regardless of order ...
+        const json_document a = json_document::parse(R"({"a": 1, "b": 2})");
+        const json_document b = json_document::parse(R"({"b": 2, "a": 1})");
+        std::cout << (a.root() != b.root()) << '\n';
+    
+        // ... but ordered_json (ordered_map) compares them in the order they
+        // appear, so the very same reordering is detected as a difference
+        const ordered_json_document oa = ordered_json_document::parse(R"({"a": 1, "b": 2})");
+        const ordered_json_document ob = ordered_json_document::parse(R"({"b": 2, "a": 1})");
+        std::cout << (oa.root() != ob.root()) << '\n';
+    }
+    
+    ```
+
+    Output:
+
+    ```json
+    true
+    false
+    true
+    
+    ```
+
+## See also
+
+- [operator==](operator_eq.md) - compare for equality
+- [materialize](materialize.md) - build a `BasicJsonType` value, e.g. to keep comparing after the document is gone
+- [`BasicJsonType::operator!=`](../basic_json/operator_ne.md) - the corresponding function of `basic_json`
+
+## Version history
+
+- Added in version 3.13.0.