Merge pull request #1307 from eudoxos/ringbuffer-sink

Add ringbuffer sink

include/spdlog/details/circular_q.h

@@ -72,6 +72,27 @@ public:
         return v_[head_];
     }
 
+    // Return number of elements actually stored
+    size_t size() const
+    {
+        if (tail_ >= head_)
+        {
+           return tail_ - head_;
+        }
+        else
+        {
+            return max_items_ - (head_ - tail_ );
+        }
+    }
+
+    // Return const reference to item by index.
+    // If index is out of range 0…size()-1, the behavior is undefined.
+    const T &at(size_t i) const
+    {
+        assert(i < size());
+        return v_[(head_+ i) % max_items_];
+    }
+
     // Pop item from front.
     // If there are no elements in the container, the behavior is undefined.
     void pop_front()