diff --git a/include/backtrace/Backtrace.h b/include/backtrace/Backtrace.h
index bf4efd3..df40b87 100644
--- a/include/backtrace/Backtrace.h
+++ b/include/backtrace/Backtrace.h
@@ -60,6 +60,7 @@
   // Create a string representing the formatted line of backtrace information
   // for a single frame.
   virtual std::string FormatFrameData(size_t frame_num);
+  virtual std::string FormatFrameData(const backtrace_frame_data_t* frame);
 
   pid_t Pid() { return backtrace_.pid; }
   pid_t Tid() { return backtrace_.tid; }
@@ -68,9 +69,16 @@
   const backtrace_t* GetBacktrace() { return &backtrace_; }
 
   const backtrace_frame_data_t* GetFrame(size_t frame_num) {
+    if (frame_num > NumFrames()) {
+      return NULL;
+    }
     return &backtrace_.frames[frame_num];
   }
 
+  const backtrace_map_info_t* GetMapList() {
+    return map_info_;
+  }
+
 protected:
   Backtrace(BacktraceImpl* impl, pid_t pid, backtrace_map_info_t* map_info);
 
diff --git a/include/backtrace/backtrace.h b/include/backtrace/backtrace.h
index fa81f21..cfcbf0f 100644
--- a/include/backtrace/backtrace.h
+++ b/include/backtrace/backtrace.h
@@ -44,6 +44,7 @@
 } backtrace_map_info_t;
 
 typedef struct {
+  size_t num;             /* The current fame number. */
   uintptr_t pc;           /* The absolute pc. */
   uintptr_t sp;           /* The top of the stack. */
   size_t stack_size;      /* The size of the stack, zero indicate an unknown stack size. */