From c4eedd6ae487f8b5a2bb9658ec6d8c07a52eea8e Mon Sep 17 00:00:00 2001
From: Rosen Penev <rosenp@gmail.com>
Date: Tue, 29 Mar 2022 18:47:04 -0700
Subject: [PATCH] nodiscard addition

Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 include/exiv2/basicio.hpp    | 48 +++++++++++++--------------
 include/exiv2/bmffimage.hpp  | 10 +++---
 include/exiv2/bmpimage.hpp   |  2 +-
 include/exiv2/cr2image.hpp   |  6 ++--
 include/exiv2/crwimage.hpp   |  6 ++--
 include/exiv2/datasets.hpp   | 20 +++++------
 include/exiv2/epsimage.hpp   |  2 +-
 include/exiv2/error.hpp      |  6 ++--
 include/exiv2/exif.hpp       | 64 ++++++++++++++++++------------------
 include/exiv2/gifimage.hpp   |  2 +-
 include/exiv2/image.hpp      | 34 +++++++++----------
 include/exiv2/iptc.hpp       | 56 +++++++++++++++----------------
 include/exiv2/jp2image.hpp   |  2 +-
 include/exiv2/jpgimage.hpp   |  6 ++--
 include/exiv2/properties.hpp | 18 +++++-----
 samples/prevtest.cpp         |  2 ++
 samples/write-test.cpp       |  2 ++
 17 files changed, 145 insertions(+), 141 deletions(-)

diff --git a/include/exiv2/basicio.hpp b/include/exiv2/basicio.hpp
index 42480d51..daada21b 100644
--- a/include/exiv2/basicio.hpp
+++ b/include/exiv2/basicio.hpp
@@ -201,25 +201,25 @@ class EXIV2API BasicIo {
     @return Offset from the start of IO if successful;<BR>
            -1 if failure;
    */
-  virtual long tell() const = 0;
+  [[nodiscard]] virtual long tell() const = 0;
   /*!
     @brief Get the current size of the IO source in bytes.
     @return Size of the IO source in bytes;<BR>
            -1 if failure;
    */
-  virtual size_t size() const = 0;
+  [[nodiscard]] virtual size_t size() const = 0;
   //! Returns true if the IO source is open, otherwise false.
-  virtual bool isopen() const = 0;
+  [[nodiscard]] virtual bool isopen() const = 0;
   //! Returns 0 if the IO source is in a valid state, otherwise nonzero.
-  virtual int error() const = 0;
+  [[nodiscard]] virtual int error() const = 0;
   //! Returns true if the IO position has reached the end, otherwise false.
-  virtual bool eof() const = 0;
+  [[nodiscard]] virtual bool eof() const = 0;
   /*!
     @brief Return the path to the IO resource. Often used to form
         comprehensive error messages where only a BasicIo instance is
         available.
    */
-  virtual const std::string &path() const noexcept = 0;
+  [[nodiscard]] virtual const std::string &path() const noexcept = 0;
 
   /*!
     @brief Mark all the bNone blocks to bKnow. This avoids allocating memory
@@ -442,22 +442,22 @@ class EXIV2API FileIo : public BasicIo {
     @return Offset from the start of the file if successful;<BR>
            -1 if failure;
    */
-  long tell() const override;
+  [[nodiscard]] long tell() const override;
   /*!
     @brief Flush any buffered writes and get the current file size
         in bytes.
     @return Size of the file in bytes;<BR>
            -1 if failure;
    */
-  size_t size() const override;
+  [[nodiscard]] size_t size() const override;
   //! Returns true if the file is open, otherwise false.
-  bool isopen() const override;
+  [[nodiscard]] bool isopen() const override;
   //! Returns 0 if the file is in a valid state, otherwise nonzero.
-  int error() const override;
+  [[nodiscard]] int error() const override;
   //! Returns true if the file position has reached the end, otherwise false.
-  bool eof() const override;
+  [[nodiscard]] bool eof() const override;
   //! Returns the path of the file
-  const std::string &path() const noexcept override;
+  [[nodiscard]] const std::string &path() const noexcept override;
 
   /*!
     @brief Mark all the bNone blocks to bKnow. This avoids allocating memory
@@ -624,21 +624,21 @@ class EXIV2API MemIo : public BasicIo {
     @brief Get the current IO position.
     @return Offset from the start of the memory block
    */
-  long tell() const override;
+  [[nodiscard]] long tell() const override;
   /*!
     @brief Get the current memory buffer size in bytes.
     @return Size of the in memory data in bytes;<BR>
            -1 if failure;
    */
-  size_t size() const override;
+  [[nodiscard]] size_t size() const override;
   //! Always returns true
-  bool isopen() const override;
+  [[nodiscard]] bool isopen() const override;
   //! Always returns 0
-  int error() const override;
+  [[nodiscard]] int error() const override;
   //! Returns true if the IO position has reached the end, otherwise false.
-  bool eof() const override;
+  [[nodiscard]] bool eof() const override;
   //! Returns a dummy path, indicating that memory access is used
-  const std::string &path() const noexcept override;
+  [[nodiscard]] const std::string &path() const noexcept override;
 
   /*!
     @brief Mark all the bNone blocks to bKnow. This avoids allocating memory
@@ -868,21 +868,21 @@ class EXIV2API RemoteIo : public BasicIo {
     @brief Get the current IO position.
     @return Offset from the start of the memory block
    */
-  long tell() const override;
+  [[nodiscard]] long tell() const override;
   /*!
     @brief Get the current memory buffer size in bytes.
     @return Size of the in memory data in bytes;<BR>
            -1 if failure;
    */
-  size_t size() const override;
+  [[nodiscard]] size_t size() const override;
   //! Returns true if the memory area is allocated.
-  bool isopen() const override;
+  [[nodiscard]] bool isopen() const override;
   //! Always returns 0
-  int error() const override;
+  [[nodiscard]] int error() const override;
   //! Returns true if the IO position has reached the end, otherwise false.
-  bool eof() const override;
+  [[nodiscard]] bool eof() const override;
   //! Returns the URL of the file.
-  const std::string &path() const noexcept override;
+  [[nodiscard]] const std::string &path() const noexcept override;
 
   /*!
     @brief Mark all the bNone blocks to bKnow. This avoids allocating memory
diff --git a/include/exiv2/bmffimage.hpp b/include/exiv2/bmffimage.hpp
index 42cfe2ac..94984a9e 100644
--- a/include/exiv2/bmffimage.hpp
+++ b/include/exiv2/bmffimage.hpp
@@ -26,7 +26,7 @@ struct Iloc {
   uint32_t start_;
   uint32_t length_;
 
-  std::string toString() const;
+  [[nodiscard]] std::string toString() const;
 };  // class Iloc
 
 // *****************************************************************************
@@ -105,9 +105,9 @@ class EXIV2API BmffImage : public Image {
 
   //! @name Accessors
   //@{
-  std::string mimeType() const override /* override */;
-  uint32_t pixelWidth() const override;
-  uint32_t pixelHeight() const override;
+  [[nodiscard]] std::string mimeType() const override /* override */;
+  [[nodiscard]] uint32_t pixelWidth() const override;
+  [[nodiscard]] uint32_t pixelHeight() const override;
   //@}
 
   const Exiv2::ByteOrder endian_{Exiv2::bigEndian};
@@ -123,7 +123,7 @@ class EXIV2API BmffImage : public Image {
     @warning This function should only be called by readMetadata()
    */
   long boxHandler(std::ostream& out, Exiv2::PrintStructureOption option, const long pbox_end, int depth);
-  std::string indent(int i) const {
+  [[nodiscard]] std::string indent(int i) const {
     return std::string(2 * i, ' ');
   }
 
diff --git a/include/exiv2/bmpimage.hpp b/include/exiv2/bmpimage.hpp
index eb535227..3d3b1b9a 100644
--- a/include/exiv2/bmpimage.hpp
+++ b/include/exiv2/bmpimage.hpp
@@ -70,7 +70,7 @@ class EXIV2API BmpImage : public Image {
 
   //! @name Accessors
   //@{
-  std::string mimeType() const override;
+  [[nodiscard]] std::string mimeType() const override;
   //@}
 };  // class BmpImage
 
diff --git a/include/exiv2/cr2image.hpp b/include/exiv2/cr2image.hpp
index efd948e2..fdf93a3e 100644
--- a/include/exiv2/cr2image.hpp
+++ b/include/exiv2/cr2image.hpp
@@ -66,9 +66,9 @@ class EXIV2API Cr2Image : public Image {
 
   //! @name Accessors
   //@{
-  std::string mimeType() const override;
-  uint32_t pixelWidth() const override;
-  uint32_t pixelHeight() const override;
+  [[nodiscard]] std::string mimeType() const override;
+  [[nodiscard]] uint32_t pixelWidth() const override;
+  [[nodiscard]] uint32_t pixelHeight() const override;
   //@}
 
   //! @name NOT implemented
diff --git a/include/exiv2/crwimage.hpp b/include/exiv2/crwimage.hpp
index 7ce322a0..09f8278c 100644
--- a/include/exiv2/crwimage.hpp
+++ b/include/exiv2/crwimage.hpp
@@ -68,9 +68,9 @@ class EXIV2API CrwImage : public Image {
 
   //! @name Accessors
   //@{
-  std::string mimeType() const override;
-  uint32_t pixelWidth() const override;
-  uint32_t pixelHeight() const override;
+  [[nodiscard]] std::string mimeType() const override;
+  [[nodiscard]] uint32_t pixelWidth() const override;
+  [[nodiscard]] uint32_t pixelHeight() const override;
   //@}
 
   //! @name NOT Implemented
diff --git a/include/exiv2/datasets.hpp b/include/exiv2/datasets.hpp
index e76e20a8..898724ac 100644
--- a/include/exiv2/datasets.hpp
+++ b/include/exiv2/datasets.hpp
@@ -272,21 +272,21 @@ class EXIV2API IptcKey : public Key {
 
   //! @name Accessors
   //@{
-  std::string key() const override;
-  const char* familyName() const override;
+  [[nodiscard]] std::string key() const override;
+  [[nodiscard]] const char* familyName() const override;
   /*!
     @brief Return the name of the group (the second part of the key).
            For IPTC keys, the group name is the record name.
   */
-  std::string groupName() const override;
-  std::string tagName() const override;
-  std::string tagLabel() const override;
-  uint16_t tag() const override;
-  UniquePtr clone() const;
+  [[nodiscard]] std::string groupName() const override;
+  [[nodiscard]] std::string tagName() const override;
+  [[nodiscard]] std::string tagLabel() const override;
+  [[nodiscard]] uint16_t tag() const override;
+  [[nodiscard]] UniquePtr clone() const;
   //! Return the name of the record
-  std::string recordName() const;
+  [[nodiscard]] std::string recordName() const;
   //! Return the record id
-  uint16_t record() const;
+  [[nodiscard]] uint16_t record() const;
   //@}
 
  protected:
@@ -309,7 +309,7 @@ class EXIV2API IptcKey : public Key {
 
  private:
   //! Internal virtual copy constructor.
-  IptcKey* clone_() const override;
+  [[nodiscard]] IptcKey* clone_() const override;
 
   uint16_t tag_;     //!< Tag value
   uint16_t record_;  //!< Record value
diff --git a/include/exiv2/epsimage.hpp b/include/exiv2/epsimage.hpp
index 83573ed2..9da714a1 100644
--- a/include/exiv2/epsimage.hpp
+++ b/include/exiv2/epsimage.hpp
@@ -70,7 +70,7 @@ class EXIV2API EpsImage : public Image {
 
   //! @name Accessors
   //@{
-  std::string mimeType() const override;
+  [[nodiscard]] std::string mimeType() const override;
   //@}
 
   //! @name NOT Implemented
diff --git a/include/exiv2/error.hpp b/include/exiv2/error.hpp
index 90d18174..408eef0a 100644
--- a/include/exiv2/error.hpp
+++ b/include/exiv2/error.hpp
@@ -262,17 +262,17 @@ class EXIV2API Error : public std::exception {
   }
 
   //! Virtual destructor. (Needed because of throw())
-  virtual ~Error() noexcept;
+  ~Error() noexcept override;
   //@}
 
   //! @name Accessors
   //@{
-  ErrorCode code() const noexcept;
+  [[nodiscard]] ErrorCode code() const noexcept;
   /*!
     @brief Return the error message as a C-string. The pointer returned by what()
            is valid only as long as the BasicError object exists.
    */
-  const char* what() const noexcept override;
+  [[nodiscard]] const char* what() const noexcept override;
   //@}
 
  private:
diff --git a/include/exiv2/exif.hpp b/include/exiv2/exif.hpp
index 9c212d34..c052513a 100644
--- a/include/exiv2/exif.hpp
+++ b/include/exiv2/exif.hpp
@@ -135,18 +135,18 @@ class EXIV2API Exifdatum : public Metadatum {
   //! @name Accessors
   //@{
   //! Return the key of the %Exifdatum.
-  std::string key() const override;
-  const char* familyName() const override;
-  std::string groupName() const override;
-  std::string tagName() const override;
-  std::string tagLabel() const override;
-  uint16_t tag() const override;
+  [[nodiscard]] std::string key() const override;
+  [[nodiscard]] const char* familyName() const override;
+  [[nodiscard]] std::string groupName() const override;
+  [[nodiscard]] std::string tagName() const override;
+  [[nodiscard]] std::string tagLabel() const override;
+  [[nodiscard]] uint16_t tag() const override;
   //! Return the IFD id as an integer. (Do not use, this is meant for library internal use.)
-  int ifdId() const;
+  [[nodiscard]] int ifdId() const;
   //! Return the name of the IFD
-  const char* ifdName() const;
+  [[nodiscard]] const char* ifdName() const;
   //! Return the index (unique id of this key within the original IFD)
-  int idx() const;
+  [[nodiscard]] int idx() const;
   /*!
     @brief Write value to a data buffer and return the number
            of bytes written.
@@ -161,25 +161,25 @@ class EXIV2API Exifdatum : public Metadatum {
   size_t copy(byte* buf, ByteOrder byteOrder) const override;
   std::ostream& write(std::ostream& os, const ExifData* pMetadata = nullptr) const override;
   //! Return the type id of the value
-  TypeId typeId() const override;
+  [[nodiscard]] TypeId typeId() const override;
   //! Return the name of the type
-  const char* typeName() const override;
+  [[nodiscard]] const char* typeName() const override;
   //! Return the size in bytes of one component of this type
-  size_t typeSize() const override;
+  [[nodiscard]] size_t typeSize() const override;
   //! Return the number of components in the value
-  size_t count() const override;
+  [[nodiscard]] size_t count() const override;
   //! Return the size of the value in bytes
-  size_t size() const override;
+  [[nodiscard]] size_t size() const override;
   //! Return the value as a string.
-  std::string toString() const override;
-  std::string toString(size_t n) const override;
-  int64_t toInt64(size_t n = 0) const override;
-  float toFloat(size_t n = 0) const override;
-  Rational toRational(size_t n = 0) const override;
-  Value::UniquePtr getValue() const override;
-  const Value& value() const override;
+  [[nodiscard]] std::string toString() const override;
+  [[nodiscard]] std::string toString(size_t n) const override;
+  [[nodiscard]] int64_t toInt64(size_t n = 0) const override;
+  [[nodiscard]] float toFloat(size_t n = 0) const override;
+  [[nodiscard]] Rational toRational(size_t n = 0) const override;
+  [[nodiscard]] Value::UniquePtr getValue() const override;
+  [[nodiscard]] const Value& value() const override;
   //! Return the size of the data area.
-  size_t sizeDataArea() const;
+  [[nodiscard]] size_t sizeDataArea() const;
   /*!
     @brief Return a copy of the data area of the value. The caller owns
            this copy and %DataBuf ensures that it will be deleted.
@@ -192,7 +192,7 @@ class EXIV2API Exifdatum : public Metadatum {
             %DataBuf if the value does not have a data area assigned or the
             value is not set.
    */
-  DataBuf dataArea() const;
+  [[nodiscard]] DataBuf dataArea() const;
   //@}
 
  private:
@@ -227,7 +227,7 @@ class EXIV2API ExifThumbC {
     @brief Return the thumbnail image in a %DataBuf. The caller owns the
            data buffer and %DataBuf ensures that it will be deleted.
    */
-  DataBuf copy() const;
+  [[nodiscard]] DataBuf copy() const;
   /*!
     @brief Write the thumbnail image to a file.
 
@@ -238,17 +238,17 @@ class EXIV2API ExifThumbC {
     @param path File name of the thumbnail without extension.
     @return The number of bytes written.
   */
-  size_t writeFile(const std::string& path) const;
+  [[nodiscard]] size_t writeFile(const std::string& path) const;
   /*!
     @brief Return the MIME type of the thumbnail, either \c "image/tiff"
            or \c "image/jpeg".
    */
-  const char* mimeType() const;
+  [[nodiscard]] const char* mimeType() const;
   /*!
     @brief Return the file extension for the format of the thumbnail
            (".tif" or ".jpg").
    */
-  const char* extension() const;
+  [[nodiscard]] const char* extension() const;
   //@}
 
  private:
@@ -442,24 +442,24 @@ class EXIV2API ExifData {
   //! @name Accessors
   //@{
   //! Begin of the metadata
-  const_iterator begin() const {
+  [[nodiscard]] const_iterator begin() const {
     return exifMetadata_.begin();
   }
   //! End of the metadata
-  const_iterator end() const {
+  [[nodiscard]] const_iterator end() const {
     return exifMetadata_.end();
   }
   /*!
     @brief Find the first Exifdatum with the given \em key, return a const
            iterator to it.
    */
-  const_iterator findKey(const ExifKey& key) const;
+  [[nodiscard]] const_iterator findKey(const ExifKey& key) const;
   //! Return true if there is no Exif metadata
-  bool empty() const {
+  [[nodiscard]] bool empty() const {
     return exifMetadata_.empty();
   }
   //! Get the number of metadata entries
-  size_t count() const {
+  [[nodiscard]] size_t count() const {
     return exifMetadata_.size();
   }
   //@}
diff --git a/include/exiv2/gifimage.hpp b/include/exiv2/gifimage.hpp
index 2b805753..f0df8677 100644
--- a/include/exiv2/gifimage.hpp
+++ b/include/exiv2/gifimage.hpp
@@ -73,7 +73,7 @@ class EXIV2API GifImage : public Image {
 
   //! @name Accessors
   //@{
-  std::string mimeType() const override;
+  [[nodiscard]] std::string mimeType() const override;
   //@}
 
 };  // class GifImage
diff --git a/include/exiv2/image.hpp b/include/exiv2/image.hpp
index 7bd19c6f..5ec73227 100644
--- a/include/exiv2/image.hpp
+++ b/include/exiv2/image.hpp
@@ -206,7 +206,7 @@ class EXIV2API Image {
   /*!
     @brief return iccProfile
    */
-  virtual const DataBuf& iccProfile() const {
+  [[nodiscard]] virtual const DataBuf& iccProfile() const {
     return iccProfile_;
   }
 
@@ -337,12 +337,12 @@ class EXIV2API Image {
     @brief Return the byte order in which the Exif metadata of the image is
            encoded. Initially, it is not set (\em invalidByteOrder).
    */
-  ByteOrder byteOrder() const;
+  [[nodiscard]] ByteOrder byteOrder() const;
 
   /*! @brief Check if the Image instance is valid. Use after object construction.
     @return true if the Image is in a valid state.
    */
-  bool good() const;
+  [[nodiscard]] bool good() const;
   /*!
     @brief Return the MIME type of the image.
 
@@ -353,15 +353,15 @@ class EXIV2API Image {
     and thus they all have MIME type "image/tiff", although a more
     specific MIME type may exist (e.g., "image/x-nikon-nef").
    */
-  virtual std::string mimeType() const = 0;
+  [[nodiscard]] virtual std::string mimeType() const = 0;
   /*!
     @brief Return the pixel width of the image.
    */
-  virtual uint32_t pixelWidth() const;
+  [[nodiscard]] virtual uint32_t pixelWidth() const;
   /*!
     @brief Return the pixel height of the image.
    */
-  virtual uint32_t pixelHeight() const;
+  [[nodiscard]] virtual uint32_t pixelHeight() const;
   /*!
     @brief Returns an ExifData instance containing currently buffered
         Exif data.
@@ -373,7 +373,7 @@ class EXIV2API Image {
 
     @return read only ExifData instance containing Exif values
    */
-  virtual const ExifData& exifData() const;
+  [[nodiscard]] virtual const ExifData& exifData() const;
   /*!
     @brief Returns an IptcData instance containing currently buffered
         IPTC data.
@@ -385,7 +385,7 @@ class EXIV2API Image {
 
     @return modifiable IptcData instance containing IPTC values
    */
-  virtual const IptcData& iptcData() const;
+  [[nodiscard]] virtual const IptcData& iptcData() const;
   /*!
     @brief Returns an XmpData instance containing currently buffered
         XMP data.
@@ -397,15 +397,15 @@ class EXIV2API Image {
 
     @return modifiable XmpData instance containing XMP values
    */
-  virtual const XmpData& xmpData() const;
+  [[nodiscard]] virtual const XmpData& xmpData() const;
   /*!
     @brief Return a copy of the image comment. May be an empty string.
    */
-  virtual std::string comment() const;
+  [[nodiscard]] virtual std::string comment() const;
   /*!
     @brief Return the raw XMP packet as a string.
    */
-  virtual const std::string& xmpPacket() const;
+  [[nodiscard]] virtual const std::string& xmpPacket() const;
   /*!
     @brief Return a reference to the BasicIo instance being used for Io.
 
@@ -420,23 +420,23 @@ class EXIV2API Image {
        Image class will not see those changes until the readMetadata()
        method is called.
    */
-  virtual BasicIo& io() const;
+  [[nodiscard]] virtual BasicIo& io() const;
   /*!
     @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.
    */
-  AccessMode checkMode(MetadataId metadataId) const;
+  [[nodiscard]] AccessMode checkMode(MetadataId metadataId) const;
   /*!
     @brief Check if image supports a particular type of metadata.
        This method is deprecated. Use checkMode() instead.
    */
-  bool supportsMetadata(MetadataId metadataId) const;
+  [[nodiscard]] bool supportsMetadata(MetadataId metadataId) const;
   //! Return the flag indicating the source when writing XMP metadata.
-  bool writeXmpFromPacket() const;
+  [[nodiscard]] bool writeXmpFromPacket() const;
   //! Return list of native previews. This is meant to be used only by the PreviewManager.
-  const NativePreviewList& nativePreviews() const;
+  [[nodiscard]] const NativePreviewList& nativePreviews() const;
   //@}
 
   //! set type support for this image format
@@ -446,7 +446,7 @@ class EXIV2API Image {
   }
 
   //! set type support for this image format
-  ImageType imageType() const {
+  [[nodiscard]] ImageType imageType() const {
     return imageType_;
   }
 
diff --git a/include/exiv2/iptc.hpp b/include/exiv2/iptc.hpp
index 69f9e328..56dde0e5 100644
--- a/include/exiv2/iptc.hpp
+++ b/include/exiv2/iptc.hpp
@@ -94,39 +94,39 @@ class EXIV2API Iptcdatum : public Metadatum {
            is not necessarily unique, i.e., an IptcData object may contain
            multiple metadata with the same key.
    */
-  std::string key() const override;
+  [[nodiscard]] std::string key() const override;
   /*!
      @brief Return the name of the record (deprecated)
      @return record name
    */
-  std::string recordName() const;
+  [[nodiscard]] std::string recordName() const;
   /*!
      @brief Return the record id
      @return record id
    */
-  uint16_t record() const;
-  const char* familyName() const override;
-  std::string groupName() const override;
+  [[nodiscard]] uint16_t record() const;
+  [[nodiscard]] const char* familyName() const override;
+  [[nodiscard]] std::string groupName() const override;
   /*!
      @brief Return the name of the tag (aka dataset)
      @return tag name
    */
-  std::string tagName() const override;
-  std::string tagLabel() const override;
+  [[nodiscard]] std::string tagName() const override;
+  [[nodiscard]] std::string tagLabel() const override;
   //! Return the tag (aka dataset) number
-  uint16_t tag() const override;
-  TypeId typeId() const override;
-  const char* typeName() const override;
-  size_t typeSize() const override;
-  size_t count() const override;
-  size_t size() const override;
-  std::string toString() const override;
-  std::string toString(size_t n) const override;
-  int64_t toInt64(size_t n = 0) const override;
-  float toFloat(size_t n = 0) const override;
-  Rational toRational(size_t n = 0) const override;
-  Value::UniquePtr getValue() const override;
-  const Value& value() const override;
+  [[nodiscard]] uint16_t tag() const override;
+  [[nodiscard]] TypeId typeId() const override;
+  [[nodiscard]] const char* typeName() const override;
+  [[nodiscard]] size_t typeSize() const override;
+  [[nodiscard]] size_t count() const override;
+  [[nodiscard]] size_t size() const override;
+  [[nodiscard]] std::string toString() const override;
+  [[nodiscard]] std::string toString(size_t n) const override;
+  [[nodiscard]] int64_t toInt64(size_t n = 0) const override;
+  [[nodiscard]] float toFloat(size_t n = 0) const override;
+  [[nodiscard]] Rational toRational(size_t n = 0) const override;
+  [[nodiscard]] Value::UniquePtr getValue() const override;
+  [[nodiscard]] const Value& value() const override;
   //@}
 
  private:
@@ -224,38 +224,38 @@ class EXIV2API IptcData {
   //! @name Accessors
   //@{
   //! Begin of the metadata
-  const_iterator begin() const {
+  [[nodiscard]] const_iterator begin() const {
     return iptcMetadata_.begin();
   }
   //! End of the metadata
-  const_iterator end() const {
+  [[nodiscard]] const_iterator end() const {
     return iptcMetadata_.end();
   }
   /*!
     @brief Find the first Iptcdatum with the given key, return a const
            iterator to it.
    */
-  const_iterator findKey(const IptcKey& key) const;
+  [[nodiscard]] const_iterator findKey(const IptcKey& key) const;
   /*!
     @brief Find the first Iptcdatum with the given record and dataset
            number, return a const iterator to it.
    */
-  const_iterator findId(uint16_t dataset, uint16_t record = IptcDataSets::application2) const;
+  [[nodiscard]] const_iterator findId(uint16_t dataset, uint16_t record = IptcDataSets::application2) const;
   //! Return true if there is no IPTC metadata
-  bool empty() const {
+  [[nodiscard]] bool empty() const {
     return count() == 0;
   }
 
   //! Get the number of metadata entries
-  size_t count() const {
+  [[nodiscard]] size_t count() const {
     return iptcMetadata_.size();
   }
 
   //! @brief Return the exact size of all contained IPTC metadata
-  size_t size() const;
+  [[nodiscard]] size_t size() const;
 
   //! @brief Return the metadata charset name or 0
-  const char* detectCharset() const;
+  [[nodiscard]] const char* detectCharset() const;
 
   //!  @brief dump iptc formatted binary data (used by printStructure kpsRecursive)
   static void printStructure(std::ostream& out, const Slice<byte*>& bytes, uint32_t depth);
diff --git a/include/exiv2/jp2image.hpp b/include/exiv2/jp2image.hpp
index 0955f8f0..1799311a 100644
--- a/include/exiv2/jp2image.hpp
+++ b/include/exiv2/jp2image.hpp
@@ -61,7 +61,7 @@ class EXIV2API Jp2Image : public Image {
 
   //! @name Accessors
   //@{
-  std::string mimeType() const override;
+  [[nodiscard]] std::string mimeType() const override;
   //@}
 
   //! @name NOT Implemented
diff --git a/include/exiv2/jpgimage.hpp b/include/exiv2/jpgimage.hpp
index 4ffd0a8b..58a93b9d 100644
--- a/include/exiv2/jpgimage.hpp
+++ b/include/exiv2/jpgimage.hpp
@@ -241,7 +241,7 @@ class EXIV2API JpegBase : public Image {
     @return the next Jpeg segment marker if successful;<BR>
             throws an Error if not successful
    */
-  byte advanceToMarker(ErrorCode err) const;
+  [[nodiscard]] byte advanceToMarker(ErrorCode err) const;
   //@}
 
   DataBuf readNextSegment(byte marker);
@@ -282,7 +282,7 @@ class EXIV2API JpegImage : public JpegBase {
   //@}
   //! @name Accessors
   //@{
-  std::string mimeType() const override;
+  [[nodiscard]] std::string mimeType() const override;
   //@}
 
   // NOT Implemented
@@ -343,7 +343,7 @@ class EXIV2API ExvImage : public JpegBase {
   //@}
   //! @name Accessors
   //@{
-  std::string mimeType() const override;
+  [[nodiscard]] std::string mimeType() const override;
   //@}
 
   // NOT Implemented
diff --git a/include/exiv2/properties.hpp b/include/exiv2/properties.hpp
index 1c51c0cc..2823e597 100644
--- a/include/exiv2/properties.hpp
+++ b/include/exiv2/properties.hpp
@@ -254,28 +254,28 @@ class EXIV2API XmpKey : public Key {
 
   //! @name Accessors
   //@{
-  std::string key() const override;
-  const char* familyName() const override;
+  [[nodiscard]] std::string key() const override;
+  [[nodiscard]] const char* familyName() const override;
   /*!
     @brief Return the name of the group (the second part of the key).
            For XMP keys, the group name is the schema prefix name.
   */
-  std::string groupName() const override;
-  std::string tagName() const override;
-  std::string tagLabel() const override;
+  [[nodiscard]] std::string groupName() const override;
+  [[nodiscard]] std::string tagName() const override;
+  [[nodiscard]] std::string tagLabel() const override;
   //! Properties don't have a tag number. Return 0.
-  uint16_t tag() const override;
+  [[nodiscard]] uint16_t tag() const override;
 
-  UniquePtr clone() const;
+  [[nodiscard]] UniquePtr clone() const;
 
   // Todo: Should this be removed? What about tagLabel then?
   //! Return the schema namespace for the prefix of the key
-  std::string ns() const;
+  [[nodiscard]] std::string ns() const;
   //@}
 
  private:
   //! Internal virtual copy constructor.
-  XmpKey* clone_() const override;
+  [[nodiscard]] XmpKey* clone_() const override;
 
   // Pimpl idiom
   struct Impl;
diff --git a/samples/prevtest.cpp b/samples/prevtest.cpp
index 5354c5ba..4ef44141 100644
--- a/samples/prevtest.cpp
+++ b/samples/prevtest.cpp
@@ -30,6 +30,8 @@ int main(int argc, char* const argv[]) try {
 
     Exiv2::PreviewImage preview = loader.getPreviewImage(pos);
     auto s = preview.writeFile(filename + "_" + Exiv2::toString(pos.width_) + "x" + Exiv2::toString(pos.height_));
+    if (s == 0)
+      return EXIT_FAILURE;
   }
 
   // Cleanup
diff --git a/samples/write-test.cpp b/samples/write-test.cpp
index 0ea614e9..d62c66da 100644
--- a/samples/write-test.cpp
+++ b/samples/write-test.cpp
@@ -149,6 +149,8 @@ void testCase(const std::string& file1, const std::string& file2, const std::str
   std::cerr << "---> Writing Exif thumbnail to file " << thumb << ".*\n";
   ExifThumbC et2(ed2);
   auto s = et2.writeFile(thumb);
+  if (s == 0)
+    std::cerr << "---> Failed to write to file " << thumb << ".*\n";
 }
 
 // *****************************************************************************