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api/basic_json_document/node_count/index.md

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+# nlohmann::basic_json_document::node_count
+
+```
+std::size_t node_count() const noexcept;
+```
+
+Returns the number of entries in the document's flat index.
+
+## Return value
+
+The number of index entries: one per value (of any type, at any nesting depth) plus one per object key. `0` for a [discarded](https://json.nlohmann.me/api/basic_json_document/is_discarded/index.md) document.
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Constant.
+
+## Notes
+
+Each index entry is [16 bytes](https://json.nlohmann.me/home/architecture/#node-index-of-json-views), so `node_count() * 16` is the size of the index itself (part, but not all, of [`memory_usage()`](https://json.nlohmann.me/api/basic_json_document/memory_usage/index.md), which also counts decoded strings and, for an owned document, the text).
+
+## Examples
+
+Example
+
+```
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using json_document = nlohmann::json_document;
+
+int main()
+{
+    // node_count() is the size of the flat index: one 16-byte node per value,
+    // plus one per object key (values and keys are all the index stores)
+    json_document scalar = json_document::parse("42");
+    std::cout << scalar.node_count() << '\n';
+
+    json_document doc = json_document::parse(R"({"a": 1, "b": [1, 2]})");
+    std::cout << doc.node_count() << '\n';
+}
+```
+
+Output:
+
+```
+1
+7
+```
+
+## See also
+
+- [memory_usage](https://json.nlohmann.me/api/basic_json_document/memory_usage/index.md) - the number of bytes held by the document
+- [shrink_to_fit](https://json.nlohmann.me/api/basic_json_document/shrink_to_fit/index.md) - release unused index capacity
+
+## Version history
+
+- Added in version 3.13.0 unreleased.