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

pdbApp/pvif.cpp

@@ -19,6 +19,7 @@
 #include <pv/reftrack.h>
 
 #define epicsExportSharedSymbols
+#include "sb.h"
 #include "pvif.h"
 
 #include <epicsExport.h>
@@ -37,22 +38,22 @@ namespace pvd = epics::pvData;
 
 DBCH::DBCH(dbChannel *ch) :chan(ch)
 {
-    if(!chan)
-        throw std::invalid_argument("NULL channel");
-    if(dbChannelOpen(chan)) {
-        dbChannelDelete(chan);
-        throw std::invalid_argument("Failed to open channel");
-    }
+    prepare();
 }
 
 DBCH::DBCH(const std::string& name)
     :chan(dbChannelCreate(name.c_str()))
+{
+    prepare();
+}
+
+void DBCH::prepare()
 {
     if(!chan)
         throw std::invalid_argument("NULL channel");
     if(dbChannelOpen(chan)) {
         dbChannelDelete(chan);
-        throw std::invalid_argument("Failed to open channel "+name);
+        throw std::invalid_argument(SB()<<"Failed to open channel "<<dbChannelName(chan));
     }
 }
 

pdbApp/pvif.h

@@ -61,6 +61,7 @@ struct epicsShareClass DBCH {
 private:
     DBCH(const DBCH&);
     DBCH& operator=(const DBCH&);
+    void prepare();
 };
 
 struct pdbRecordInfo {