MT#64469 AmUtils: fix str2int (double) helper

It's been noticed actually no result is written
by the reference given to a funciton helper.

Also it's not convenient with a rest of other
helpers, which return either true/false
on successfull or failed conversion, but just
directly return the result of atof() as a bool,
which is a mistake.

Also add a comment to a function declaration.

Change-Id: I4f18ce527638a3575ef7446a549650a951a0b583

core/AmUtils.cpp

@@ -269,8 +269,27 @@ bool str2int(const string& str, int& result)
 
 bool str2int(const string& str, double& result)
 {
-  char* s = (char*)str.c_str();
-  return atof(s);
+  try
+  {
+    size_t pos;
+    result = std::stod(str, &pos);
+
+    /* check whether the whole stirng was converted */
+    if (pos != str.length())
+      return false;
+
+    return true;
+  }
+  catch (const std::invalid_argument)
+  {
+    return false;
+  }
+  catch (const std::out_of_range)
+  {
+    return false;
+  }
+
+  return false;
 }
 
 bool str2int(char*& str, int& result, char sep)

core/AmUtils.h

@@ -143,6 +143,12 @@ bool str2int(char*& str, unsigned int& result, char sep = ' ');
  */
 bool str2int(const string& str, int& result);
 
+/**
+ * Convert a string to the double.
+ * @param str    [in]  string to convert.
+ * @param result [out] result integer.
+ * @return true on success
+ */
 bool str2int(const string& str, double& result);
 
 /**