diff --git a/src/allocator.h b/src/allocator.h
index 5f092d7ac..f9234270b 100644
--- a/src/allocator.h
+++ b/src/allocator.h
@@ -137,7 +137,7 @@ static inline int NCNN_XADD(int* addr, int delta)
     return tmp;
 }
 #endif
-#else // NCNN_THREADS
+#else  // NCNN_THREADS
 static inline int NCNN_XADD(int* addr, int delta)
 {
     int tmp = *addr;
diff --git a/src/simplestl.cpp b/src/simplestl.cpp
index 5c23c6fd1..6c0352d75 100644
--- a/src/simplestl.cpp
+++ b/src/simplestl.cpp
@@ -18,46 +18,42 @@
 
 #include <stdlib.h>
 
-void* operator new(size_t sz) noexcept
+void* operator new(size_t size)
 {
-    void* ptr = malloc(sz);
-    return ptr;
+    return malloc(size);
 }
 
-void* operator new(size_t sz, void* ptr) noexcept
+void* operator new(size_t /*size*/, void* ptr)
 {
     return ptr;
 }
 
-void* operator new[](size_t sz) noexcept
+void* operator new[](size_t size)
 {
-    void* ptr = malloc(sz);
-    return ptr;
+    return malloc(size);
 }
 
-void* operator new[](size_t sz, void* ptr) noexcept
+void* operator new[](size_t /*size*/, void* ptr)
 {
     return ptr;
 }
 
-void operator delete(void* ptr)noexcept
+void operator delete(void* ptr)
 {
     free(ptr);
 }
 
-void operator delete(void* ptr, size_t sz)noexcept
+void operator delete(void* /*ptr*/, void* /*voidptr2*/)
 {
-    free(ptr);
 }
 
-void operator delete[](void* ptr) noexcept
+void operator delete[](void* ptr)
 {
     free(ptr);
 }
 
-void operator delete[](void* ptr, size_t sz) noexcept
+void operator delete[](void* /*ptr*/, void* /*voidptr2*/)
 {
-    free(ptr);
 }
 
 extern "C" void __cxa_pure_virtual()
diff --git a/src/simplestl.h b/src/simplestl.h
index 18232adaa..3572d58ba 100644
--- a/src/simplestl.h
+++ b/src/simplestl.h
@@ -26,14 +26,14 @@
 #else
 
 // operator new and delete
-void* operator new(size_t sz) noexcept;
-void* operator new(size_t sz, void*) noexcept;
-void* operator new[](size_t sz) noexcept;
-void* operator new[](size_t sz, void*) noexcept;
-void operator delete(void* ptr)noexcept;
-void operator delete(void* ptr, size_t sz)noexcept;
-void operator delete[](void* ptr) noexcept;
-void operator delete[](void* ptr, size_t sz) noexcept;
+void* operator new(size_t size);
+void* operator new(size_t size, void* ptr);
+void* operator new[](size_t size);
+void* operator new[](size_t size, void* ptr);
+void operator delete(void* ptr);
+void operator delete(void* ptr, void* voidptr2);
+void operator delete[](void* ptr);
+void operator delete[](void* ptr, void* voidptr2);
 
 #endif
 
@@ -121,11 +121,11 @@ struct node
     T data_;
 
     node()
-        : prev_(nullptr), next_(nullptr), data_()
+        : prev_(0), next_(0), data_()
     {
     }
     node(const T& t)
-        : prev_(nullptr), next_(nullptr), data_(t)
+        : prev_(0), next_(0), data_(t)
     {
     }
 };
@@ -134,7 +134,7 @@ template<typename T>
 struct iter_list
 {
     iter_list()
-        : curr_(nullptr)
+        : curr_(0)
     {
     }
     iter_list(node<T>* n)
@@ -244,7 +244,7 @@ struct list
         {
             head_ = head_->next_;
             delete head_->prev_;
-            head_->prev_ = nullptr;
+            head_->prev_ = 0;
             --count_;
         }
     }
@@ -271,7 +271,7 @@ struct list
         if (count_ == 0)
         {
             head_ = new node<T>(t);
-            head_->prev_ = nullptr;
+            head_->prev_ = 0;
             head_->next_ = tail_;
             tail_->prev_ = head_;
             count_ = 1;
@@ -295,7 +295,7 @@ struct list
             if (temp == head_)
             {
                 ++pos;
-                temp->next_->prev_ = nullptr;
+                temp->next_->prev_ = 0;
                 head_ = temp->next_;
             }
             else
@@ -339,10 +339,10 @@ template<typename RandomAccessIter, typename Compare>
 void partial_sort(RandomAccessIter first, RandomAccessIter middle, RandomAccessIter last, Compare comp)
 {
     // [TODO] heap sort should be used here, but we simply use bubble sort now
-    for (auto i = first; i < middle; ++i)
+    for (RandomAccessIter i = first; i < middle; ++i)
     {
         // bubble sort
-        for (auto j = last - 1; j > first; --j)
+        for (RandomAccessIter j = last - 1; j > first; --j)
         {
             if (comp(*j, *(j - 1)))
             {
@@ -356,9 +356,11 @@ template<typename T>
 struct vector
 {
     vector()
+        : data_(0), size_(0), capacity_(0)
     {
     }
     vector(const size_t new_size, const T& value = T())
+        : data_(0), size_(0), capacity_(0)
     {
         resize(new_size, value);
     }
@@ -367,6 +369,7 @@ struct vector
         clear();
     }
     vector(const vector& v)
+        : data_(0), size_(0), capacity_(0)
     {
         resize(v.size());
         for (size_t i = 0; i < size_; i++)
@@ -417,7 +420,7 @@ struct vector
             data_[i].~T();
         }
         delete[](char*) data_;
-        data_ = nullptr;
+        data_ = 0;
         size_ = 0;
         capacity_ = 0;
     }
@@ -456,7 +459,7 @@ struct vector
 
     void insert(T* pos, T* b, T* e)
     {
-        vector* v = nullptr;
+        vector* v = 0;
         if (b >= begin() && b < end())
         {
             //the same vector
@@ -488,9 +491,9 @@ struct vector
     }
 
 protected:
-    T* data_ = nullptr;
-    size_t size_ = 0;
-    size_t capacity_ = 0;
+    T* data_;
+    size_t size_;
+    size_t capacity_;
     void try_alloc(size_t new_size)
     {
         if (new_size * 3 / 2 > capacity_ / 2)