ObjectId constructor translates a hex string (24 characters) into a 12 byte object id

MongoDB/include/Poco/MongoDB/ObjectId.h

@@ -46,8 +46,12 @@ class MongoDB_API ObjectId
 public:
 	typedef SharedPtr<ObjectId> Ptr;
 
-	ObjectId(const std::string& id = "");
-		/// Constructor
+	ObjectId(const std::string& id);
+		/// Constructor. The string must contain a hexidecimal representation
+		/// of an object id. This means a string of 24 characters.
+
+	ObjectId(const ObjectId& copy);
+		/// Copy constructor.
 
 	virtual ~ObjectId();
 		/// Destructor
@@ -61,10 +65,19 @@ public:
 		/// of the ID char array.
 
 private:
+
+	ObjectId();
+		/// Constructor. Creates an empty Id
+
 	unsigned char _id[12];
 
 	friend class BSONWriter;
 	friend class BSONReader;
+	friend class Document;
+	
+	static int fromHex(char c);
+	
+	static char fromHex(const char* c);
 };
 
 
@@ -79,6 +92,21 @@ inline Timestamp ObjectId::timestamp() const
 	return Timestamp::fromEpochTime((time_t) time);
 }
 
+inline int ObjectId::fromHex(char c)
+{
+	if ( '0' <= c && c <= '9' )
+		return c - '0';
+	if ( 'a' <= c && c <= 'f' )
+		return c - 'a' + 10;
+	if ( 'A' <= c && c <= 'F' )
+		return c - 'A' + 10;
+	return 0xff;
+}
+
+inline char ObjectId::fromHex(const char* c)
+{
+	return (char)((fromHex(c[0]) << 4 ) | fromHex(c[1]));
+}
 
 // BSON Embedded Document
 // spec: ObjectId
@@ -89,7 +117,7 @@ struct ElementTraits<ObjectId::Ptr>
 
 	static std::string toString(const ObjectId::Ptr& id,
 		int indent = 0,
-		const std::string& fmt = "%x")
+		const std::string& fmt = "%02x")
 	{
 		return id->toString(fmt);
 	}