add nullptr to perform_search

we need a nullptr at the end, to show where the list ends.

libtrie_loader.cpp

@@ -0,0 +1,84 @@
+#include <xcdat.hpp>
+#include <string>
+#include <iostream>
+#include <vector>
+#include <string.h> // for strdup 
+
+typedef void* TrieHandle;  // Opaque pointer to represent the trie in C
+
+struct Entry {
+  const std::string_view decoded_view;
+  const uint64_t id;
+  inline Entry(const std::string_view decoded_view, const uint64_t id) : decoded_view(decoded_view), id(id) {}
+};
+
+
+TrieHandle load_trie_from_cstring(const char* cstr) {
+    // Convert C-style string to C++ string
+    std::string dict_file(cstr);
+
+    // Print the file path to ensure it's correct
+        
+    try {
+        // Load the trie object (using xcdat::load)
+        xcdat::trie_15_type* trie = new xcdat::trie_15_type(xcdat::load<xcdat::trie_15_type>(dict_file));
+        return reinterpret_cast<TrieHandle>(trie);  // Return the pointer as an opaque handle
+    } catch (const std::exception& e) {
+        // Catch any exceptions related to loading the trie and print a friendly message
+        
+        // Return nullptr to indicate failure
+        return nullptr;
+    }
+}
+
+
+const char** search_prefix(TrieHandle handle, const char* search_str, size_t* result_count) {
+    xcdat::trie_15_type* trie = reinterpret_cast<xcdat::trie_15_type*>(handle);
+    xcdat::trie_15_type::prefix_iterator itr = trie->make_prefix_iterator(search_str);
+
+    std::vector<std::string> results;
+
+    while (itr.next()) {
+        results.push_back(std::string(itr.decoded_view()));
+    }
+
+    // Allocate memory to store the results + 1 for the null terminator
+    *result_count = results.size();
+    const char** result_array = new const char*[*result_count + 1]; // +1 for null pointer
+
+    // Copy the results from the vector to the array
+    for (size_t i = 0; i < *result_count; ++i) {
+        result_array[i] = strdup(results[i].c_str()); // Dynamically allocate strings
+    }
+
+    // Add a null terminator
+    result_array[*result_count] = nullptr;
+
+    return result_array;
+}
+
+
+
+// C territory
+
+// Wrapper function to load the trie, for C usage
+extern "C" TrieHandle load_trie(const char* dict_file) {
+    return load_trie_from_cstring(dict_file);
+}
+
+// Wrapper function to perform a search and return results, for C usage
+extern "C" const char** perform_search(TrieHandle handle, const char* search_str, size_t* result_count) {
+    return search_prefix(handle, search_str, result_count);
+}
+
+// Function to free the memory allocated for the trie (opaque pointer)
+extern "C" void free_trie(TrieHandle handle) {
+    xcdat::trie_15_type* trie = reinterpret_cast<xcdat::trie_15_type*>(handle);
+    delete trie;
+}
+
+// Function to free the memory allocated for search results (const char**)
+extern "C" void free_search_results(const char** results) {
+    delete[] results;
+}
+