deploy: 4155e2938f

examples/basic_json_view__contains_json_pointer.cpp

@@ -0,0 +1,39 @@
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using json_document = nlohmann::json_document;
+using json_pointer = nlohmann::json::json_pointer;
+
+int main()
+{
+    // "retry_of" is only present on some records, nested a level down
+    // inside "meta"
+    json_document batch = json_document::parse(R"(
+      [
+        {"id": 1, "meta": {}},
+        {"id": 2, "meta": {"retry_of": 1}}
+      ]
+    )");
+
+    const auto records = batch.root();
+    const json_pointer retry_of("/meta/retry_of");
+    for (std::size_t i = 0; i < records.size(); ++i)
+    {
+        const auto record = records[i];
+        if (record.contains(retry_of))
+        {
+            std::cout << "record " << i << " is a retry of " << record[retry_of].get<int>() << '\n';
+        }
+        else
+        {
+            std::cout << "record " << i << " is original\n";
+        }
+    }
+
+    // contains() with a JSON pointer never throws -- not even for a
+    // pointer that indexes into a primitive ("/0/id/x") or uses a
+    // malformed array index ("/01"), either of which would need a
+    // try/catch with json::contains(ptr)
+    std::cout << std::boolalpha << records.contains(json_pointer("/0/id/x")) << '\n';
+    std::cout << std::boolalpha << records.contains(json_pointer("/01")) << '\n';
+}