Changed behaviour of unsupport Image functions to throw. Added better method to query the supported metadata functions for each image type. Fixes bug #491.

src/Makefile

@@ -66,7 +66,6 @@ CCSRC =  basicio.cpp          \
 	 fujimn.cpp           \
 	 ifd.cpp              \
 	 image.cpp            \
-	 imgreg.cpp           \
 	 iptc.cpp             \
 	 jpgimage.cpp         \
 	 makernote.cpp        \

src/cr2image.cpp

@@ -103,16 +103,21 @@ namespace Exiv2 {
         return isThisType(*io_, false);
     }
 
+    AccessMode Cr2Image::checkMode(MetadataId metadataId) const
+    {
+        return ImageFactory::checkMode(ImageType::cr2, metadataId);
+    }
+
     void Cr2Image::clearMetadata()
     {
         clearExifData();
-        clearComment();
+        clearIptcData();
     }
 
     void Cr2Image::setMetadata(const Image& image)
     {
         setExifData(image.exifData());
-        setComment(image.comment());
+        setIptcData(image.iptcData());
     }
 
     void Cr2Image::clearExifData()
@@ -137,12 +142,13 @@ namespace Exiv2 {
 
     void Cr2Image::clearComment()
     {
-        comment_.erase();
+        // not supported, do nothing
     }
 
-    void Cr2Image::setComment(const std::string& comment)
+    void Cr2Image::setComment(const std::string& /*comment*/)
     {
-        comment_ = comment;
+        // not supported
+        throw(Error(32, "Image comment", "CR2"));
     }
 
     void Cr2Image::readMetadata()
@@ -167,44 +173,10 @@ namespace Exiv2 {
 
     void Cr2Image::writeMetadata()
     {
-/*
+        /*
-
           Todo: implement me!
-
+         */
-#ifdef DEBUG
+        throw(Error(31, "metadata", "CR2"));
-        std::cerr << "Writing CR2 file " << io_->path() << "\n";
-#endif
-        // Read existing image
-        DataBuf buf;
-        if (io_->open() == 0) {
-            IoCloser closer(*io_);
-            // Ensure that this is the correct image type
-            if (isThisType(*io_, false)) {
-                // Read the image into a memory buffer
-                buf.alloc(io_->size());
-                io_->read(buf.pData_, buf.size_);
-                if (io_->error() || io_->eof()) {
-                    buf.reset();
-                }
-            }
-        }
-
-        // Parse image, starting with a CR2 header component
-        Cr2Header::AutoPtr head(new Cr2Header);
-        if (buf.size_ != 0) {
-            head->read(buf.pData_, buf.size_);
-        }
-
-        Blob blob;
-        Cr2Parser::encode(blob, head.get(), this);
-
-        // Write new buffer to file
-        BasicIo::AutoPtr tempIo(io_->temporary()); // may throw
-        assert (tempIo.get() != 0);
-        tempIo->write(&blob[0], static_cast<long>(blob.size()));
-        io_->close();
-        io_->transfer(*tempIo); // may throw
-*/
     } // Cr2Image::writeMetadata
 
     bool Cr2Image::isThisType(BasicIo& iIo, bool advance) const

src/cr2image.hpp

@@ -95,13 +95,17 @@ namespace Exiv2 {
         void            readMetadata();
         /*!
           @brief Todo: Write metadata back to the image. This method is not
-                 yet implemented.
+              yet implemented. Calling it will throw an Error(31).
          */
         void            writeMetadata();
         void            setExifData(const ExifData& exifData);
         void            clearExifData();
         void            setIptcData(const IptcData& iptcData);
         void            clearIptcData();
+        /*!
+          @brief Not supported. CR2 format does not contain a comment.
+              Calling this function will throw an Error(32).
+         */
         void            setComment(const std::string& comment);
         void            clearComment();
         void            setMetadata(const Image& image);
@@ -117,6 +121,7 @@ namespace Exiv2 {
         const IptcData& iptcData() const { return iptcData_; }
         std::string     comment()  const { return comment_; }
         BasicIo&        io()       const { return *io_; }
+        AccessMode      checkMode(MetadataId metadataId) const;
         //@}
 
     private:

src/crwimage.cpp

@@ -182,6 +182,11 @@ namespace Exiv2 {
         return isThisType(*io_, false);
     }
 
+    AccessMode CrwImage::checkMode(MetadataId metadataId) const
+    {
+        return ImageFactory::checkMode(ImageType::crw, metadataId);
+    }
+
     void CrwImage::clearMetadata()
     {
         clearExifData();
@@ -206,12 +211,13 @@ namespace Exiv2 {
 
     void CrwImage::clearIptcData()
     {
-        // not supported
+        // not supported, do nothing
     }
 
     void CrwImage::setIptcData(const IptcData& /*iptcData*/)
     {
         // not supported
+        throw(Error(32, "IPTC metadata", "CRW"));
     }
 
     void CrwImage::clearComment()

src/crwimage.hpp

@@ -83,7 +83,7 @@ namespace Exiv2 {
 
     /*!
       @brief Class to access raw Canon Crw images. Only Exif metadata and a
-             comment are supported. Crw format does not contain Iptc metadata.
+             comment are supported. Crw format does not contain IPTC metadata.
      */
     class CrwImage : public Image {
         friend bool isCrwType(BasicIo& iIo, bool advance);
@@ -122,22 +122,14 @@ namespace Exiv2 {
         //! @name Manipulators
         //@{
         void            readMetadata();
-        /*!
-          @brief Todo: Write metadata back to the image. This method is not
-                 yet implemented.
-         */
         void            writeMetadata();
         void            setExifData(const ExifData& exifData);
         void            clearExifData();
         /*!
-          @brief Not supported. Crw format does not contain Iptc metadata.
+          @brief Not supported. CRW format does not contain IPTC metadata.
-                 Calling this function will do nothing.
+              Calling this function will throw an Error(32).
          */
         void            setIptcData(const IptcData& iptcData);
-        /*!
-          @brief Not supported. Crw format does not contain Iptc metadata.
-                 Calling this function will do nothing.
-         */
         void            clearIptcData();
         void            setComment(const std::string& comment);
         void            clearComment();
@@ -154,6 +146,7 @@ namespace Exiv2 {
         const IptcData& iptcData() const { return iptcData_; }
         std::string     comment()  const { return comment_; }
         BasicIo&        io()       const { return *io_; }
+        AccessMode      checkMode(MetadataId metadataId) const;
         //@}
 
     private:

src/error.cpp

@@ -73,8 +73,8 @@ namespace Exiv2 {
         ErrMsg( 28, N_("Invalid charset: `%1'")), // %1=charset name
         ErrMsg( 29, N_("Unsupported date format")),
         ErrMsg( 30, N_("Unsupported time format")),
-        ErrMsg( 31, N_("%1: CRW images don't support IPTC metadata")), // %1=function
+        ErrMsg( 31, N_("Writing %1 to %2 images is not supported")), // %1=metadata type, %2=image format
-        ErrMsg( 32, N_("%1: CRW images don't support JPEG comments")), // %1=function
+        ErrMsg( 32, N_("%1 in %2 images is not supported")), // %1=metadata type, %2=image format
         ErrMsg( 33, N_("This does not look like a CRW image")),
         ErrMsg( 34, N_("%1: Not supported")), // %1=function
         ErrMsg( 35, N_("ImageFactory registry full")),

src/image.cpp

@@ -44,6 +44,15 @@ EXIV2_RCSID("@(#) $Id$")
 #include "error.hpp"
 #include "futils.hpp"
 
+#include "jpgimage.hpp"
+#include "cr2image.hpp"
+#include "crwimage.hpp"
+#include "mrwimage.hpp"
+#include "tiffimage.hpp"
+#ifdef EXV_HAVE_LIBZ
+# include "pngimage.hpp"
+#endif // EXV_HAVE_LIBZ
+
 // + standard includes
 #include <cerrno>
 #include <cstdio>
@@ -62,31 +71,50 @@ EXIV2_RCSID("@(#) $Id$")
 // class member definitions
 namespace Exiv2 {
 
-    bool Image::supportsMetadata(MetadataId metadataId) const
+    const ImageFactory::Registry ImageFactory::registry_[] = {
+        //image type       creation fct     type check  Exif mode    IPTC mode    Comment mode
+        //---------------  ---------------  ----------  -----------  -----------  ------------
+        { ImageType::jpeg, newJpegInstance, isJpegType, amReadWrite, amReadWrite, amReadWrite },
+        { ImageType::exv,  newExvInstance,  isExvType,  amReadWrite, amReadWrite, amReadWrite },
+        { ImageType::cr2,  newCr2Instance,  isCr2Type,  amRead,      amRead,      amNone      },
+        { ImageType::crw,  newCrwInstance,  isCrwType,  amReadWrite, amNone,      amReadWrite },
+        { ImageType::mrw,  newMrwInstance,  isMrwType,  amRead,      amRead,      amNone      },
+        { ImageType::tiff, newTiffInstance, isTiffType, amRead,      amRead,      amNone      },
+#ifdef EXV_HAVE_LIBZ
+        { ImageType::png,  newPngInstance,  isPngType,  amRead,      amRead,      amNone      },
+#endif // EXV_HAVE_LIBZ
+        // End of list marker
+        { ImageType::none, 0,               0,          amNone,      amNone,      amNone      }
+    };
+
+    bool ImageFactory::Registry::operator==(const int& imageType) const
     {
-        return (supportedMetadata_ & metadataId) != 0;
+        return imageType == imageType_;
     }
 
-    const ImageFactory::Registry* ImageFactory::find(int imageType)
+    bool Image::supportsMetadata(MetadataId metadataId) const
     {
-        for (unsigned int i = 0; registry_[i].imageType_ != ImageType::none; ++i) {
+        return (supportedMetadata_ & metadataId) != 0;
-            if (registry_[i].imageType_ == imageType) return &registry_[i];
-        }
-        return 0;
     }
 
-    void ImageFactory::registerImage(int            type,
+    AccessMode ImageFactory::checkMode(int imageType, MetadataId metadataId)
-                                     NewInstanceFct newInst,
-                                     IsThisTypeFct  isType)
     {
-        unsigned int i = 0;
+        const Registry* r = find(registry_, imageType);
-        for (; i < MAX_IMAGE_FORMATS; ++i) {
+        if (!r) throw Error(13, imageType);
-            if (registry_[i].imageType_ == ImageType::none) {
+        AccessMode am = amNone;
-                registry_[i] = Registry(type, newInst, isType);
+        switch (metadataId) {
+        case mdExif:
+            am = r->exifSupport_;
             break;
+        case mdIptc:
+            am = r->iptcSupport_;
+            break;
+        case mdComment:
+            am = r->commentSupport_;
+            break;
+        // no default: let the compiler complain
         }
-        }
+        return am;
-        if (i == MAX_IMAGE_FORMATS) throw Error(35);
     }
 
     int ImageFactory::getType(const std::string& path)
@@ -169,7 +197,7 @@ namespace Exiv2 {
                                         BasicIo::AutoPtr io)
     {
         // BasicIo instance does not need to be open
-        const Registry* r = find(type);
+        const Registry* r = find(registry_, type);
         if (0 != r) {
             return r->newInstance_(io, true);
         }

src/image.hpp

@@ -235,9 +235,17 @@ namespace Exiv2 {
              Image class will not see those changes until the readMetadata()
              method is called.
          */
-        virtual BasicIo& io() const = 0;
+        virtual BasicIo& io() const =0;
+        /*!
+          @brief Returns the access mode, i.e., the metadata functions, which 
+             this image supports for the metadata type \em metadataId.
+          @param metadataId The metadata identifier.
+          @return Access mode for the requested image type and metadata identifier.
+         */
+        virtual AccessMode checkMode(MetadataId metadataId) const =0;
         /*!
           @brief Check if image supports a particular type of metadata.
+             This method is deprecated. Use checkMode() instead.
          */
         bool supportsMetadata(MetadataId metadataId) const;
         //@}
@@ -274,27 +282,6 @@ namespace Exiv2 {
     */
     class ImageFactory {
     public:
-        //! @name Manipulators
-        //@{
-        /*!
-          @brief Register image type together with its function pointers.
-
-          The image factory creates new images by calling their associated
-          function pointer. Additional images can be added by registering
-          new type and function pointers. If called for a type that already
-          exists in the list, the corresponding functions are replaced.
-
-          @param type Image type.
-          @param newInst Function pointer for creating image instances.
-          @param isType Function pointer to test for matching image types.
-        */
-        static void registerImage(int type,
-                                  NewInstanceFct newInst,
-                                  IsThisTypeFct isType);
-        //@}
-
-        //! @name Accessors
-        //@{
         /*!
           @brief Create an Image subclass of the appropriate type by reading
               the specified file. %Image type is derived from the file
@@ -394,9 +381,31 @@ namespace Exiv2 {
           @return %Image type or Image::none if the type is not recognized.
          */
         static int getType(BasicIo& io);
-        //@}
+        /*!
+          @brief Returns the access mode or supported metadata functions for an 
+              image type and a metadata type.
+          @param imageType  The image type.
+          @param metadataId The metadata identifier.
+          @return Access mode for the requested image type and metadata identifier.
+          @throw Error(13) if the image type is not supported.
+         */
+        static AccessMode checkMode(int imageType, MetadataId metadataId);
 
     private:
+        //! Struct for storing image types and function pointers.
+        struct Registry {
+            //! Comparison operator to compare a Registry structure with an image type
+            bool operator==(const int& imageType) const;
+
+            // DATA
+            int            imageType_;
+            NewInstanceFct newInstance_;
+            IsThisTypeFct  isThisType_;
+            AccessMode     exifSupport_;
+            AccessMode     iptcSupport_;
+            AccessMode     commentSupport_;
+        };
+
         //! @name Creators
         //@{
         //! Prevent construction: not implemented.
@@ -405,35 +414,9 @@ namespace Exiv2 {
         ImageFactory(const ImageFactory& rhs);
         //@}
 
-        //! Struct for storing image types and function pointers.
-        struct Registry
-        {
-            //! Default constructor
-            Registry()
-                : imageType_(ImageType::none),
-                  newInstance_(0),
-                  isThisType_(0)
-                {}
-            //! Constructor
-            Registry(int            imageType,
-                     NewInstanceFct newInstance,
-                     IsThisTypeFct  isThisType)
-                : imageType_(imageType),
-                  newInstance_(newInstance),
-                  isThisType_(isThisType)
-                {}
-            int            imageType_;
-            NewInstanceFct newInstance_;
-            IsThisTypeFct  isThisType_;
-        };
-
-        //! Return the registry entry for type
-        static const Registry* find(int imageType);
-
         // DATA
-        static const unsigned int MAX_IMAGE_FORMATS = 32;
+        //! List of image types, creation functions and access modes
-        //! List of image types and corresponding creation functions.
+        static const Registry registry_[];
-        static Registry registry_[MAX_IMAGE_FORMATS];
     }; // class ImageFactory
 
     //! Helper class modelling the TIFF header structure.

src/imgreg.cpp

@@ -1,62 +0,0 @@
-// ***************************************************************** -*- C++ -*-
-/*
- * Copyright (C) 2005, 2006 Andreas Huggel <ahuggel@gmx.net>
- *
- * This program is part of the Exiv2 distribution.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version 2
- * of the License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, 5th Floor, Boston, MA 02110-1301 USA.
- */
-/*
-  File:      imgreg.cpp
-  Version:   $Rev$
-  Author(s): Andreas Huggel (ahu) <ahuggel@gmx.net>
-  History:   19-Sep-05, ahu: created
-
- */
-// *****************************************************************************
-#include "rcsid.hpp"
-EXIV2_RCSID("@(#) $Id$")
-
-// *****************************************************************************
-// included header files
-#include "image.hpp"
-#include "jpgimage.hpp"
-#include "cr2image.hpp"
-#include "crwimage.hpp"
-#include "mrwimage.hpp"
-#include "tiffimage.hpp"
-#ifdef EXV_HAVE_LIBZ
-# include "pngimage.hpp"
-#endif // EXV_HAVE_LIBZ
-
-// + standard includes
-
-// *****************************************************************************
-// class member definitions
-namespace Exiv2 {
-
-    ImageFactory::Registry ImageFactory::registry_[] = {
-        Registry(ImageType::jpeg, newJpegInstance, isJpegType),
-        Registry(ImageType::exv,  newExvInstance,  isExvType),
-        Registry(ImageType::cr2,  newCr2Instance,  isCr2Type),
-        Registry(ImageType::crw,  newCrwInstance,  isCrwType),
-        Registry(ImageType::mrw,  newMrwInstance,  isMrwType),
-        Registry(ImageType::tiff, newTiffInstance, isTiffType),
-#ifdef EXV_HAVE_LIBZ
-        Registry(ImageType::png,  newPngInstance,  isPngType)
-#endif // EXV_HAVE_LIBZ
-    };
-
-}                                       // namespace Exiv2

src/jpgimage.cpp

@@ -581,6 +581,11 @@ namespace Exiv2 {
     {
     }
 
+    AccessMode JpegImage::checkMode(MetadataId metadataId) const
+    {
+        return ImageFactory::checkMode(ImageType::jpeg, metadataId);
+    }
+
     int JpegImage::writeHeader(BasicIo& outIo) const
     {
         // Jpeg header
@@ -628,6 +633,11 @@ namespace Exiv2 {
     {
     }
 
+    AccessMode ExvImage::checkMode(MetadataId metadataId) const
+    {
+        return ImageFactory::checkMode(ImageType::exv, metadataId);
+    }
+
     int ExvImage::writeHeader(BasicIo& outIo) const
     {
         // Exv header

src/jpgimage.hpp

@@ -134,15 +134,15 @@ namespace Exiv2 {
         void            clearComment();
         void            setMetadata(const Image& image);
         void            clearMetadata();
+        ExifData&       exifData()       { return exifData_; }
+        IptcData&       iptcData()       { return iptcData_; }
         //@}
 
         //! @name Accessors
         //@{
         bool            good()     const;
         const ExifData& exifData() const { return exifData_; }
-        ExifData& exifData() { return exifData_; }
         const IptcData& iptcData() const { return iptcData_; }
-        IptcData& iptcData() { return iptcData_; }
         std::string     comment()  const { return comment_; }
         BasicIo&        io()       const { return *io_; }
         //@}
@@ -283,6 +283,10 @@ namespace Exiv2 {
         //! Destructor
         ~JpegImage() {}
         //@}
+        //! @name Accessors
+        //@{
+        AccessMode checkMode(MetadataId metadataId) const;
+        //@}
     protected:
         //! @name Accessors
         //@{
@@ -339,6 +343,10 @@ namespace Exiv2 {
         //! Destructor
         ~ExvImage() {}
         //@}
+        //! @name Accessors
+        //@{
+        AccessMode checkMode(MetadataId metadataId) const;
+        //@}
     protected:
         //! @name Accessors
         //@{

src/mrwimage.cpp

@@ -70,14 +70,21 @@ namespace Exiv2 {
         return isThisType(*io_, false);
     }
 
+    AccessMode MrwImage::checkMode(MetadataId metadataId) const
+    {
+        return ImageFactory::checkMode(ImageType::mrw, metadataId);
+    }
+
     void MrwImage::clearMetadata()
     {
         clearExifData();
+        clearIptcData();
     }
 
     void MrwImage::setMetadata(const Image& image)
     {
         setExifData(image.exifData());
+        setIptcData(image.iptcData());
     }
 
     void MrwImage::clearExifData()
@@ -102,12 +109,13 @@ namespace Exiv2 {
 
     void MrwImage::clearComment()
     {
-        // not supported
+        // not supported, do nothing
     }
 
     void MrwImage::setComment(const std::string& /*comment*/)
     {
         // not supported
+        throw(Error(32, "Image comment", "MRW"));
     }
 
     void MrwImage::readMetadata()
@@ -161,44 +169,10 @@ namespace Exiv2 {
 
     void MrwImage::writeMetadata()
     {
-/*
+        /*
-
           Todo: implement me!
-
+         */
-#ifdef DEBUG
+        throw(Error(31, "metadata", "MRW"));
-        std::cerr << "Writing MRW file " << io_->path() << "\n";
-#endif
-        // Read existing image
-        DataBuf buf;
-        if (io_->open() == 0) {
-            IoCloser closer(*io_);
-            // Ensure that this is the correct image type
-            if (isThisType(*io_, false)) {
-                // Read the image into a memory buffer
-                buf.alloc(io_->size());
-                io_->read(buf.pData_, buf.size_);
-                if (io_->error() || io_->eof()) {
-                    buf.reset();
-                }
-            }
-        }
-
-        // Parse image, starting with a MRW header component
-        TiffHeade2::AutoPtr head(new TiffHeade2);
-        if (buf.size_ != 0) {
-            head->read(buf.pData_, buf.size_);
-        }
-
-        Blob blob;
-        TiffParser::encode(blob, head.get(), this);
-
-        // Write new buffer to file
-        BasicIo::AutoPtr tempIo(io_->temporary()); // may throw
-        assert (tempIo.get() != 0);
-        tempIo->write(&blob[0], static_cast<long>(blob.size()));
-        io_->close();
-        io_->transfer(*tempIo); // may throw
-*/
     } // MrwImage::writeMetadata
 
     bool MrwImage::isThisType(BasicIo& iIo, bool advance) const

src/mrwimage.hpp

@@ -94,7 +94,7 @@ namespace Exiv2 {
         void            readMetadata();
         /*!
           @brief Todo: Write metadata back to the image. This method is not
-                 yet implemented.
+              yet implemented. Calling it will throw an Error(31).
          */
         void            writeMetadata();
         void            setExifData(const ExifData& exifData);
@@ -103,13 +103,9 @@ namespace Exiv2 {
         void            clearIptcData();
         /*!
           @brief Not supported. MRW format does not contain a comment.
-                 Calling this function will do nothing.
+              Calling this function will throw an Error(32).
          */
         void            setComment(const std::string& comment);
-        /*!
-          @brief Not supported. MRW format does not contain a comment.
-                 Calling this function will do nothing.
-         */
         void            clearComment();
         void            setMetadata(const Image& image);
         void            clearMetadata();
@@ -124,6 +120,7 @@ namespace Exiv2 {
         const IptcData& iptcData() const { return iptcData_; }
         std::string     comment()  const { return comment_; }
         BasicIo&        io()       const { return *io_; }
+        AccessMode      checkMode(MetadataId metadataId) const;
         //@}
 
     private:

src/pngimage.cpp

@@ -74,14 +74,21 @@ namespace Exiv2 {
         return isThisType(*io_, false);
     }
 
+    AccessMode PngImage::checkMode(MetadataId metadataId) const
+    {
+        return ImageFactory::checkMode(ImageType::png, metadataId);
+    }
+
     void PngImage::clearMetadata()
     {
         clearExifData();
+        clearIptcData();
     }
 
     void PngImage::setMetadata(const Image& image)
     {
         setExifData(image.exifData());
+        setIptcData(image.iptcData());
     }
 
     void PngImage::clearExifData()
@@ -106,7 +113,7 @@ namespace Exiv2 {
 
     void PngImage::clearComment()
     {
-        // not yet supported.
+        // not yet supported, do nothing
         // TODO : Add 'iTXt' chunk 'Description' tag support here
     }
 
@@ -114,6 +121,7 @@ namespace Exiv2 {
     {
         // not yet supported
         // TODO : Add 'iTXt' chunk 'Description' tag support here
+        throw(Error(32, "Image comment", "PNG"));
     }
 
     void PngImage::readMetadata()
@@ -152,8 +160,9 @@ namespace Exiv2 {
     void PngImage::writeMetadata()
     {
         /*
-       TODO: implement me!
+          Todo: implement me!
          */
+        throw(Error(31, "metadata", "PNG"));
     } // PngImage::writeMetadata
 
     bool PngImage::isThisType(BasicIo& iIo, bool advance) const

src/pngimage.hpp

@@ -97,7 +97,7 @@ namespace Exiv2 {
         void            readMetadata();
         /*!
           @brief Todo: Write metadata back to the image. This method is not
-                 yet implemented.
+              yet implemented. Calling it will throw an Error(31).
          */
         void            writeMetadata();
         void            setExifData(const ExifData& exifData);
@@ -106,13 +106,10 @@ namespace Exiv2 {
         void            clearIptcData();
         /*!
           @brief Not supported. PNG format does not contain a comment.
-                 Calling this function will do nothing.
+              Calling it will throw an Error(32).<br>
+              Todo: Add 'iTXt' chunk 'Description' tag support here.
          */
         void            setComment(const std::string& comment);
-        /*!
-          @brief Not supported. PNG format does not contain a comment.
-                 Calling this function will do nothing.
-         */
         void            clearComment();
         void            setMetadata(const Image& image);
         void            clearMetadata();
@@ -127,6 +124,7 @@ namespace Exiv2 {
         const IptcData& iptcData() const { return iptcData_; }
         std::string     comment()  const { return comment_;  }
         BasicIo&        io()       const { return *io_;      }
+        AccessMode      checkMode(MetadataId metadataId) const;
         //@}
 
     private:

src/tiffimage.cpp

@@ -70,16 +70,21 @@ namespace Exiv2 {
         return isThisType(*io_, false);
     }
 
+    AccessMode TiffImage::checkMode(MetadataId metadataId) const
+    {
+        return ImageFactory::checkMode(ImageType::tiff, metadataId);
+    }
+
     void TiffImage::clearMetadata()
     {
         clearExifData();
-        clearComment();
+        clearIptcData();
     }
 
     void TiffImage::setMetadata(const Image& image)
     {
         setExifData(image.exifData());
-        setComment(image.comment());
+        setIptcData(image.iptcData());
     }
 
     void TiffImage::clearExifData()
@@ -104,12 +109,13 @@ namespace Exiv2 {
 
     void TiffImage::clearComment()
     {
-        comment_.erase();
+        // not supported, do nothing
     }
 
-    void TiffImage::setComment(const std::string& comment)
+    void TiffImage::setComment(const std::string& /*comment*/)
     {
-        comment_ = comment;
+        // not supported
+        throw(Error(32, "Image comment", "TIFF"));
     }
 
     void TiffImage::readMetadata()
@@ -134,44 +140,10 @@ namespace Exiv2 {
 
     void TiffImage::writeMetadata()
     {
-/*
+        /*
-
           Todo: implement me!
-
+         */
-#ifdef DEBUG
+        throw(Error(31, "metadata", "TIFF"));
-        std::cerr << "Writing TIFF file " << io_->path() << "\n";
-#endif
-        // Read existing image
-        DataBuf buf;
-        if (io_->open() == 0) {
-            IoCloser closer(*io_);
-            // Ensure that this is the correct image type
-            if (isThisType(*io_, false)) {
-                // Read the image into a memory buffer
-                buf.alloc(io_->size());
-                io_->read(buf.pData_, buf.size_);
-                if (io_->error() || io_->eof()) {
-                    buf.reset();
-                }
-            }
-        }
-
-        // Parse image, starting with a TIFF header component
-        TiffHeade2::AutoPtr head(new TiffHeade2);
-        if (buf.size_ != 0) {
-            head->read(buf.pData_, buf.size_);
-        }
-
-        Blob blob;
-        TiffParser::encode(blob, head.get(), this);
-
-        // Write new buffer to file
-        BasicIo::AutoPtr tempIo(io_->temporary()); // may throw
-        assert (tempIo.get() != 0);
-        tempIo->write(&blob[0], static_cast<long>(blob.size()));
-        io_->close();
-        io_->transfer(*tempIo); // may throw
-*/
     } // TiffImage::writeMetadata
 
     bool TiffImage::isThisType(BasicIo& iIo, bool advance) const

src/tiffimage.hpp

@@ -93,13 +93,17 @@ namespace Exiv2 {
         void            readMetadata();
         /*!
           @brief Todo: Write metadata back to the image. This method is not
-                 yet implemented.
+              yet implemented. Calling it will throw an Error(31).
          */
         void            writeMetadata();
         void            setExifData(const ExifData& exifData);
         void            clearExifData();
         void            setIptcData(const IptcData& iptcData);
         void            clearIptcData();
+        /*!
+          @brief Not supported. TIFF format does not contain a comment.
+              Calling this function will throw an Error(32).
+         */
         void            setComment(const std::string& comment);
         void            clearComment();
         void            setMetadata(const Image& image);
@@ -115,6 +119,7 @@ namespace Exiv2 {
         const IptcData& iptcData() const { return iptcData_; }
         std::string     comment()  const { return comment_; }
         BasicIo&        io()       const { return *io_; }
+        AccessMode      checkMode(MetadataId metadataId) const;
         //@}
 
     private:

src/types.hpp

@@ -92,6 +92,9 @@ namespace Exiv2 {
     //! An identifier for each type of metadata
     enum MetadataId { mdExif=1, mdIptc=2, mdComment=4 };
 
+    //! An identifier for each mode of metadata support
+    enum AccessMode { amNone=0, amRead=1, amWrite=2, amReadWrite=3 };
+
     //! Type identifiers for IFD format types
     enum TypeId { invalidTypeId, unsignedByte, asciiString, unsignedShort,
                   unsignedLong, unsignedRational, invalid6, undefined,