BIND 10 trac2009, updated. afc0fe7345aa86ba3eaebf1bba8f62db64760c1f [2009] Add comment about why a static_cast is necessary

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- Log -----------------------------------------------------------------
commit afc0fe7345aa86ba3eaebf1bba8f62db64760c1f
Author: Mukund Sivaraman <muks at isc.org>
Date:   Thu May 31 10:41:39 2012 +0530

    [2009] Add comment about why a static_cast is necessary

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Summary of changes:
 src/lib/xfr/xfrout_client.cc |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

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diff --git a/src/lib/xfr/xfrout_client.cc b/src/lib/xfr/xfrout_client.cc
index 1d7ce3b..af0c1b5 100644
--- a/src/lib/xfr/xfrout_client.cc
+++ b/src/lib/xfr/xfrout_client.cc
@@ -82,7 +82,12 @@ XfroutClient::sendXfroutRequestInfo(const int tcp_sock,
 
     // TODO: this shouldn't be blocking send, even though it's unlikely to
     // block.
-    // converting the 16-bit word to network byte order.
+    // Converting the 16-bit word to network byte order.
+
+    // Splitting msg_len below performs something called a 'narrowing
+    // conversion' (conversion of uint16_t to uint8_t). C++0x (and GCC
+    // 4.7) requires explicit casting when a narrowing conversion is
+    // performed. For reference, see 8.5.4/6 of n3225.
     const uint8_t lenbuf[2] = { static_cast<uint8_t>(msg_len >> 8),
                                 static_cast<uint8_t>(msg_len & 0xff) };
     if (send(impl_->socket_.native(), lenbuf, sizeof(lenbuf), 0) !=