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api/basic_json_view/front.md

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+# <small>nlohmann::basic_json_view::</small>front
+
+```cpp
+basic_json_view front() const;
+```
+
+Returns the first element of an array, the first member value of an object, or the value itself if it is primitive
+(as for [`BasicJsonType::front()`](../basic_json/front.md), a primitive value is a range of one element).
+
+## Return value
+
+The first element or member value. For a primitive value (number, string, boolean), the value itself.
+
+## Exception safety
+
+Strong guarantee: there are no changes to the view or the document it refers to.
+
+## Exceptions
+
+Throws [`invalid_iterator.214`](../../home/exceptions.md#jsonexceptioninvalid_iterator214) if the view is
+[null](is_null.md) or [discarded](is_discarded.md), or if it is an empty array or object.
+
+This exception does not carry a [`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) path: the view has no
+`BasicJsonType` value to point at, so the exception is created without one, even if `BasicJsonType` was built with
+`JSON_DIAGNOSTICS` enabled.
+
+## Complexity
+
+Constant.
+
+## Notes
+
+Unlike [`BasicJsonType::front()`](../basic_json/front.md), which has undefined behavior for an empty array or
+object, `front()` throws `invalid_iterator.214` for an empty array, an empty object, a null value, or a discarded
+view.
+
+## Examples
+
+??? example
+
+    The example below reads only the earliest entry of a build log with `front()`, without materializing the rest
+    of the (possibly long) log.
+
+    ```cpp
+    #include <iostream>
+    #include <nlohmann/json_view.hpp>
+    
+    using json_document = nlohmann::json_document;
+    
+    int main()
+    {
+        // the build log of a running job; front() reads just the earliest event
+        // without materializing the (possibly long) rest of the log
+        json_document log = json_document::parse(R"(["queued", "started", "compiling", "linking", "done"])");
+        std::cout << log.root().front().materialize().dump() << '\n';
+    
+        // an empty log -- front() throws instead of the undefined behavior
+        // basic_json::front() has for an empty array
+        json_document empty_log = json_document::parse("[]");
+        try
+        {
+            static_cast<void>(empty_log.root().front());
+        }
+        catch (const nlohmann::json::invalid_iterator& e)
+        {
+            std::cout << e.what() << '\n';
+        }
+    }
+    
+    ```
+
+    Output:
+
+    ```json
+    "queued"
+    [json.exception.invalid_iterator.214] cannot get value
+    
+    ```
+
+## See also
+
+- [back](back.md) - access the last element
+- [`BasicJsonType::front`](../basic_json/front.md) - the corresponding function of `basic_json`
+
+## Version history
+
+- Added in version 3.13.0.