deploy: 4155e2938f

examples/basic_json_document__shrink_to_fit.cpp

@@ -0,0 +1,44 @@
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <nlohmann/json_view.hpp>
+
+using json_document = nlohmann::json_document;
+
+int main()
+{
+    std::cout << std::boolalpha;
+
+    // build a large array (many nodes), then read a small one into the same
+    // document: the index grown for the large input is still allocated
+    std::ostringstream big;
+    big << '[';
+    for (int i = 0; i < 500; ++i)
+    {
+        if (i != 0)
+        {
+            big << ',';
+        }
+        big << i;
+    }
+    big << ']';
+
+    json_document doc;
+    doc.read(big.str());
+    const std::size_t big_nodes = doc.node_count();
+
+    doc.read(std::string("[1]"));
+    std::cout << (doc.node_count() < big_nodes) << '\n'; // far fewer live nodes now
+    const std::size_t before = doc.memory_usage();
+
+    // shrink_to_fit() moves the index into a block sized for what is actually
+    // used. This INVALIDATES every view taken from this document before the
+    // call (they point into the old, now-freed block) -- take fresh ones from
+    // root() afterward.
+    doc.shrink_to_fit();
+    const std::size_t after = doc.memory_usage();
+    std::cout << (after <= before) << '\n';
+
+    // a freshly taken view is valid and correct
+    std::cout << doc.root().is_array() << ' ' << doc.root().size() << '\n';
+}