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