1 files changed, 27 insertions, 5 deletions

diff --git a/include/gnuradio/io_signature.hpp b/include/gnuradio/io_signature.hpp
index 5473721..6cab2d6 100644
--- a/include/gnuradio/io_signature.hpp
+++ b/include/gnuradio/io_signature.hpp
@@ -18,30 +18,52 @@
 #define INCLUDED_GNURADIO_IO_SIGNATURE_HPP
 
 #include <vector>
+#include <stdexcept>
 
 namespace gnuradio
 {
 
+/*!
+ * An IO signature describes the input or output specifications
+ * for the streaming input or output ports of a block.
+ * Properties are a maximum and minimum number of ports,
+ * and an item size in bytes for each port.
+ */
 struct IOSignature : std::vector<int>
 {
     static const int IO_INFINITE = -1;
 
+    //! Create an empty signature with infinite IO
     IOSignature(void)
     {
-        this->set_min_streams(0);
-        this->set_max_streams(0);
+        this->set_min_streams(IO_INFINITE);
+        this->set_max_streams(IO_INFINITE);
     }
 
+    //! Create a signature with the specified min and max streams
+    IOSignature(const int min_streams, const int max_streams)
+    {
+        if (min_streams > max_streams and max_streams != IO_INFINITE)
+        {
+            throw std::invalid_argument("io signature fail: min_streams > max_streams");
+        }
+        this->set_min_streams(min_streams);
+        this->set_max_streams(max_streams);
+    }
+
+    //! Construct from pointer for backwards compatible shared_ptr usage.
     IOSignature(const IOSignature *sig)
     {
         *this = *sig;
     }
 
+    //! Overloaded arrow operator for backwards compatible shared_ptr usage.
     IOSignature* operator->(void)
     {
         return this;
     };
 
+    //! Overloaded arrow operator for backwards compatible shared_ptr usage.
     const IOSignature* operator->(void) const
     {
         return this;
@@ -69,11 +91,11 @@ struct IOSignature : std::vector<int>
 
     int sizeof_stream_item(const int index) const
     {
-        if (int(this->size()) >= index)
+        if (this->size() > unsigned(index))
         {
-            return this->at(0);
+            return this->at(index);
         }
-        return this->at(index);
+        return this->back();
     }
 
     std::vector<int> sizeof_stream_items(void) const