pvif: DBCH cleanup

avoid some duplication

common/sb.h

@@ -0,0 +1,16 @@
+#ifndef SB_H
+#define SB_H
+
+#include <sstream>
+
+// in-line string builder (eg. for exception messages)
+//   throw std::runtime_error(SB()<<"Answer: !"<<42);
+struct SB {
+    std::ostringstream strm;
+    SB() {}
+    operator std::string() const { return strm.str(); }
+    template<typename T>
+    SB& operator<<(T i) { strm<<i; return *this; }
+};
+
+#endif // SB_H