Add peekBack() method to Istream.

src/OpenFOAM/db/IOstreams/IOstreams/Istream.C

@@ -25,13 +25,31 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "Istream.H"
-#include "bool.H"
-#include "token.H"
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
-// Set t to the put back token if there is one and return true,
-// otherwise return false
+void Foam::Istream::putBack(const token& t)
+{
+    if (bad())
+    {
+        FatalIOErrorIn("void Istream::putBack(const token&)", *this)
+            << "Attempt to put back onto bad stream"
+            << exit(FatalIOError);
+    }
+    else if (putBack_)
+    {
+        FatalIOErrorIn("void Istream::putBack(const token&)", *this)
+            << "Attempt to put back another token"
+            << exit(FatalIOError);
+    }
+    else
+    {
+        putBackToken_ = t;
+        putBack_ = true;
+    }
+}
+
+
 bool Foam::Istream::getBack(token& t)
 {
     if (bad())
@@ -39,8 +57,6 @@ bool Foam::Istream::getBack(token& t)
         FatalIOErrorIn("void Istream::getBack(token&)", *this)
             << "Attempt to get back from bad stream"
             << exit(FatalIOError);
-
-        return false;
     }
     else if (putBack_)
     {
@@ -53,26 +69,18 @@ bool Foam::Istream::getBack(token& t)
 }
 
 
-// Keep the put back token
-void Foam::Istream::putBack(const token& t)
+bool Foam::Istream::peekBack(token& t)
 {
-    if (bad())
+    if (putBack_)
     {
-        FatalIOErrorIn("void Istream::putBack(const token&)", *this)
-            << "Attempt to put back onto bad stream"
-            << exit(FatalIOError);
-    }
-    else if (putBack_)
-    {
-        FatalIOErrorIn("void Istream::putBack(const token&)", *this)
-            << "Attempt to put back another token"
-            << exit(FatalIOError);
+        t = putBackToken_;
     }
     else
     {
-        putBackToken_ = t;
-        putBack_ = true;
+        t = token::undefinedToken;
     }
+
+    return putBack_;
 }
 
 

src/OpenFOAM/db/IOstreams/IOstreams/Istream.H

@@ -62,7 +62,7 @@ class Istream
 {
     // Private data
 
-        //- Has a token been put back on the stream
+        //- Has a token been put back on the stream?
         bool putBack_;
 
         //- The last token put back on the stream
@@ -97,12 +97,19 @@ public:
         // Read functions
 
             //- Put back token
+            //  Only a single put back is permitted
             void putBack(const token&);
 
-            //- Get the put back token
+            //- Get the put back token if there is one and return true.
+            //  Return false if no put back token is available.
             bool getBack(token&);
 
-             //- Return next token from stream
+            //- Peek at the put back token without removing it.
+            //  Returns false if no put back token is available and set the
+            //  token to undefined.
+            bool peekBack(token&);
+
+            //- Return next token from stream
             virtual Istream& read(token&) = 0;
 
             //- Read a character