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api/basic_json/push_back.md

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+# <small>nlohmann::basic_json::</small>push_back
+
+```cpp
+// (1)
+void push_back(basic_json&& val);
+void push_back(const basic_json& val);
+
+// (2)
+void push_back(const typename object_t::value_type& val);
+
+// (3)
+void push_back(initializer_list_t init);
+```
+
+1. Appends the given element `val` to the end of the JSON array. If the function is called on a JSON null value, an
+   empty array is created before appending `val`.
+
+2. Inserts the given element `val` to the JSON object. If the function is called on a JSON null value, an empty object
+   is created before inserting `val`.
+
+3. This function allows using `push_back` with an initializer list. In case
+
+    1. the current value is an object,
+    2. the initializer list `init` contains only two elements, and
+    3. the first element of `init` is a string,
+
+    `init` is converted into an object element and added using `push_back(const typename object_t::value_type&)`.
+    Otherwise, `init` is converted to a JSON value and added using `push_back(basic_json&&)`.
+
+## Iterator invalidation
+
+For all cases where an element is added to an **array**, a reallocation can happen, in which case all iterators (including
+the [`end()`](end.md) iterator) and all references to the elements are invalidated. Otherwise, only the
+[`end()`](end.md) iterator is invalidated.
+
+For [`ordered_json`](../ordered_json.md), also adding an element to an **object** can yield a reallocation which again
+invalidates all iterators and all references.
+
+## Parameters
+
+`val` (in)
+:   the value to add to the JSON array/object
+
+`init` (in)
+:   an initializer list
+
+## Exceptions
+
+1. Throws [`type_error.308`](../../home/exceptions.md#jsonexceptiontype_error308) when called on a type other than
+   JSON array or null; example: `"cannot use push_back() with number"`
+2. Throws [`type_error.308`](../../home/exceptions.md#jsonexceptiontype_error308) when called on a type other than
+   JSON object or null; example: `"cannot use push_back() with number"`
+3. Throws [`type_error.308`](../../home/exceptions.md#jsonexceptiontype_error308) when called on a type other than
+   JSON array or null; example: `"cannot use push_back() with number"`
+
+## Complexity
+
+1. Amortized constant.
+2. Logarithmic in the size of the container, O(log(`size()`)).
+3. Linear in the size of the initializer list `init`.
+
+## Notes
+
+(3) This function is required to resolve an ambiguous overload error, because pairs like `{"key", "value"}` can be both
+    interpreted as `object_t::value_type` or `std::initializer_list<basic_json>`, see
+    [#235](https://github.com/nlohmann/json/issues/235) for more information.
+
+## Examples
+
+??? example "Example: (1) add element to array"
+
+    The example shows how `push_back()` and `+=` can be used to add elements to a JSON array. Note how the `null` value
+    was silently converted to a JSON array.
+    
+    ```cpp
+    --8<-- "examples/push_back.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/push_back.output"
+    ```
+
+??? example "Example: (2) add element to object"
+
+    The example shows how `push_back()` and `+=` can be used to add elements to a JSON object. Note how the `null` value
+    was silently converted to a JSON object.
+
+    ```cpp
+    --8<-- "examples/push_back__object_t__value.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/push_back__object_t__value.output"
+    ```
+
+??? example "Example: (3) add to object from initializer list"
+
+    The example shows how initializer lists are treated as objects when possible.
+
+    ```cpp
+    --8<-- "examples/push_back__initializer_list.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/push_back__initializer_list.output"
+    ```
+
+## See also
+
+- [emplace_back](emplace_back.md) add a value to an array
+- [operator+=](operator+=.md) add a value to an array/object
+- [Modifying values](../../features/modifying_values.md) - the article on modifying values
+
+## Version history
+
+1. Since version 1.0.0.
+2. Since version 1.0.0.
+3. Since version 2.0.0.