deploy: 4d8e7a7210

examples/reject_duplicate_keys.cpp

@@ -0,0 +1,61 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+#include <stdexcept>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+using json = nlohmann::json;
+
+json parse_strict(const std::string& input)
+{
+    // one key set per nesting depth, reused across sibling objects
+    std::vector<std::unordered_set<std::string>> keys;
+
+    auto reject_duplicate_keys = [&](int depth, json::parse_event_t event, json & parsed)
+    {
+        if (event == json::parse_event_t::object_start)
+        {
+            // keys of this object are reported at depth+1 (see the event table above)
+            const auto child_depth = static_cast<std::size_t>(depth) + 1;
+            if (keys.size() <= child_depth)
+            {
+                keys.resize(child_depth + 1);
+            }
+            keys[child_depth].clear();
+            return true;
+        }
+
+        if (event == json::parse_event_t::key)
+        {
+            auto& seen = keys[static_cast<std::size_t>(depth)];
+            const auto& key = parsed.get_ref<const std::string&>();
+            if (!seen.insert(key).second)
+            {
+                throw std::runtime_error("duplicate JSON object key: " + key);
+            }
+            return true;
+        }
+
+        return true;
+    };
+
+    return json::parse(input, reject_duplicate_keys);
+}
+
+int main()
+{
+    // parsing succeeds when all keys are unique
+    json j = parse_strict(R"({"one": 1, "two": 2})");
+    std::cout << j << '\n';
+
+    // parsing throws when a key is repeated
+    try
+    {
+        parse_strict(R"({"one": 1, "one": 2})");
+    }
+    catch (const std::exception& e)
+    {
+        std::cout << e.what() << '\n';
+    }
+}