wifi fixed vector

esphome/components/wifi/wifi_component.cpp

@@ -552,7 +552,7 @@ void WiFiComponent::start_scanning() {
 // Using insertion sort instead of std::stable_sort saves flash memory
 // by avoiding template instantiations (std::rotate, std::stable_sort, lambdas)
 // IMPORTANT: This sort is stable (preserves relative order of equal elements)
-static void insertion_sort_scan_results(std::vector<WiFiScanResult> &results) {
+static void insertion_sort_scan_results(FixedVector<WiFiScanResult> &results) {
   const size_t size = results.size();
   for (size_t i = 1; i < size; i++) {
     // Make a copy to avoid issues with move semantics during comparison

esphome/components/wifi/wifi_component.h

@@ -278,7 +278,7 @@ class WiFiComponent : public Component {
   std::string get_use_address() const;
   void set_use_address(const std::string &use_address);
 
-  const std::vector<WiFiScanResult> &get_scan_result() const { return scan_result_; }
+  const FixedVector<WiFiScanResult> &get_scan_result() const { return scan_result_; }
 
   network::IPAddress wifi_soft_ap_ip();
 
@@ -385,7 +385,7 @@ class WiFiComponent : public Component {
   std::string use_address_;
   std::vector<WiFiAP> sta_;
   std::vector<WiFiSTAPriority> sta_priorities_;
-  std::vector<WiFiScanResult> scan_result_;
+  FixedVector<WiFiScanResult> scan_result_;
   WiFiAP selected_ap_;
   WiFiAP ap_;
   optional<float> output_power_;

esphome/components/wifi/wifi_component_esp8266.cpp

@@ -696,7 +696,15 @@ void WiFiComponent::wifi_scan_done_callback_(void *arg, STATUS status) {
     this->retry_connect();
     return;
   }
+
+  // Count the number of results first
   auto *head = reinterpret_cast<bss_info *>(arg);
+  size_t count = 0;
+  for (bss_info *it = head; it != nullptr; it = STAILQ_NEXT(it, next)) {
+    count++;
+  }
+
+  this->scan_result_.init(count);
   for (bss_info *it = head; it != nullptr; it = STAILQ_NEXT(it, next)) {
     WiFiScanResult res({it->bssid[0], it->bssid[1], it->bssid[2], it->bssid[3], it->bssid[4], it->bssid[5]},
                        std::string(reinterpret_cast<char *>(it->ssid), it->ssid_len), it->channel, it->rssi,

esphome/components/wifi/wifi_component_esp_idf.cpp

@@ -763,8 +763,9 @@ void WiFiComponent::wifi_process_event_(IDFWiFiEvent *data) {
     const auto &it = data->data.sta_scan_done;
     ESP_LOGV(TAG, "Scan done: status=%" PRIu32 " number=%u scan_id=%u", it.status, it.number, it.scan_id);
 
-    scan_result_.clear();
     this->scan_done_ = true;
+    scan_result_.clear();
+
     if (it.status != 0) {
       // scan error
       return;
@@ -784,7 +785,7 @@ void WiFiComponent::wifi_process_event_(IDFWiFiEvent *data) {
     }
     records.resize(number);
 
-    scan_result_.reserve(number);
+    scan_result_.init(number);
     for (int i = 0; i < number; i++) {
       auto &record = records[i];
       bssid_t bssid;

esphome/components/wifi/wifi_component_libretiny.cpp

@@ -411,7 +411,7 @@ void WiFiComponent::wifi_scan_done_callback_() {
   if (num < 0)
     return;
 
-  this->scan_result_.reserve(static_cast<unsigned int>(num));
+  this->scan_result_.init(static_cast<unsigned int>(num));
   for (int i = 0; i < num; i++) {
     String ssid = WiFi.SSID(i);
     wifi_auth_mode_t authmode = WiFi.encryptionType(i);

esphome/core/application.cpp

@@ -340,8 +340,8 @@ void Application::calculate_looping_components_() {
     }
   }
 
-  // Pre-reserve vector to avoid reallocations
+  // Initialize FixedVector with exact size - no reallocation possible
-  this->looping_components_.reserve(total_looping);
+  this->looping_components_.init(total_looping);
 
   // Add all components with loop override that aren't already LOOP_DONE
   // Some components (like logger) may call disable_loop() during initialization

esphome/core/application.h

@@ -472,7 +472,7 @@ class Application {
   // - When a component is enabled, it's swapped with the first inactive component
   //   and active_end_ is incremented
   // - This eliminates branch mispredictions from flag checking in the hot loop
-  std::vector<Component *> looping_components_{};
+  FixedVector<Component *> looping_components_{};
 #ifdef USE_SOCKET_SELECT_SUPPORT
   std::vector<int> socket_fds_;  // Vector of all monitored socket file descriptors
 #endif

esphome/core/helpers.h

@@ -159,6 +159,80 @@ template<typename T, size_t N> class StaticVector {
   const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
 };
 
+/// Fixed-capacity vector - allocates once at runtime, never reallocates
+/// This avoids std::vector template overhead (_M_realloc_insert, _M_default_append)
+/// when size is known at initialization but not at compile time
+template<typename T> class FixedVector {
+ private:
+  T *data_{nullptr};
+  size_t size_{0};
+  size_t capacity_{0};
+
+  // Helper to destroy elements and free memory
+  void cleanup_() {
+    if (data_ != nullptr) {
+      // Manually destroy all elements
+      for (size_t i = 0; i < size_; i++) {
+        data_[i].~T();
+      }
+      // Free raw memory
+      ::operator delete(data_);
+    }
+  }
+
+ public:
+  FixedVector() = default;
+
+  ~FixedVector() { cleanup_(); }
+
+  // Disable copy to avoid accidental copies
+  FixedVector(const FixedVector &) = delete;
+  FixedVector &operator=(const FixedVector &) = delete;
+
+  // Allocate capacity - can be called multiple times to reinit
+  void init(size_t n) {
+    cleanup_();
+    data_ = nullptr;
+    capacity_ = 0;
+    size_ = 0;
+    if (n > 0) {
+      // Allocate raw memory without calling constructors
+      data_ = static_cast<T *>(::operator new(n * sizeof(T)));
+      capacity_ = n;
+    }
+  }
+
+  // Clear the vector (reset size to 0, keep capacity)
+  void clear() { size_ = 0; }
+
+  // Check if vector is empty
+  bool empty() const { return size_ == 0; }
+
+  /// Add element without bounds checking
+  /// Caller must ensure sufficient capacity was allocated via init()
+  /// Silently ignores pushes beyond capacity (no exception or assertion)
+  void push_back(const T &value) {
+    if (size_ < capacity_) {
+      // Use placement new to construct the object in pre-allocated memory
+      new (&data_[size_]) T(value);
+      size_++;
+    }
+  }
+
+  size_t size() const { return size_; }
+
+  /// Access element without bounds checking (matches std::vector behavior)
+  /// Caller must ensure index is valid (i < size())
+  T &operator[](size_t i) { return data_[i]; }
+  const T &operator[](size_t i) const { return data_[i]; }
+
+  // Iterator support for range-based for loops
+  T *begin() { return data_; }
+  T *end() { return data_ + size_; }
+  const T *begin() const { return data_; }
+  const T *end() const { return data_ + size_; }
+};
+
 ///@}
 
 /// @name Mathematics