From 2313c6ad74471aa36c48b8a273ed9cde56a6c256 Mon Sep 17 00:00:00 2001
From: Andreas Huggel <ahuggel@gmx.net>
Date: Mon, 10 May 2004 13:16:19 +0000
Subject: [PATCH] Added exifcomment sample program

---
 src/exifcomment.cpp | 162 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 162 insertions(+)
 create mode 100644 src/exifcomment.cpp

diff --git a/src/exifcomment.cpp b/src/exifcomment.cpp
new file mode 100644
index 00000000..45ed8abe
--- /dev/null
+++ b/src/exifcomment.cpp
@@ -0,0 +1,162 @@
+// ***************************************************************** -*- C++ -*-
+/*
+  Abstract : Sample program showing how to set the Exif comment of an image
+
+  File:      exifcomment.cpp
+  Version  : $Name:  $ $Revision: 1.1 $
+  Author(s): Andreas Huggel (ahu) <ahuggel@gmx.net>
+  History  : 10-May-04, ahu: created
+ */
+// *****************************************************************************
+// included header files
+#include "exif.hpp"
+#include <iostream>
+#include <iomanip>
+#include <cstring>
+
+// *****************************************************************************
+// local declarations
+
+std::string readError(int rc, const std::string& path);
+std::string writeError(int rc, const std::string& path);
+
+// *****************************************************************************
+// Main
+int main(int argc, char* const argv[])
+try {
+
+    if (argc != 2) {
+        std::cout << "Usage: " << argv[0] << " file\n";
+        return 1;
+    }
+
+    Exiv2::ExifData exifData;
+    int rc = exifData.read(argv[1]);
+    if (rc) {
+        std::string error = readError(rc, argv[1]);
+        throw Exiv2::Error(error);
+    }
+
+    /*
+      There are two pitfalls that we need to consider when setting the Exif user
+      comment (Image.UserInfo.UserComment) of an image:
+
+      First, the type of the Exif user comment tag is "undefined" (and not
+      ASCII) according to the Exif standard. This means that in Exiv2, we have
+      to deal with a DataValue (and not an AsciiValue). DataValue has the usual
+      two read methods, however, the one taking a const std::string& buf expects
+      the string to contain a series of integers (e.g., "0 1 2") and not a text
+      string. Thus, we need to use the read function that reads the value from a
+      character buffer of a given length.
+
+      Second, the Exif comment field starts with an eight character area that
+      identifies the used character set. For ASCII, these eight characters are
+      "ASCII\0\0\0". The actual comment follows after this code.
+
+      Note: There is a more simple Exif tag for the title of an image. It is a
+      20 byte string (type ASCII) and does not store two-byte characters.
+      (Image.OtherTags.ImageDescription)
+     */
+
+    // Initialise a data value with the character set and comment
+    std::string charset("ASCII\0\0\0", 8);
+    std::string comment("A comment added to the Exif metadata through Exiv2");
+    Exiv2::DataValue value;
+    value.read((charset + comment).data(), 8 + comment.size());
+
+    // Set the Exif comment
+    std::string key = "Image.UserInfo.UserComment";
+    Exiv2::ExifData::iterator pos = exifData.findKey(key);
+    if (pos != exifData.end()) {
+        // Use the existing Exif UserComment metadatum if there is one
+        pos->setValue(&value);
+    }
+    else {
+        // Otherwise add a new UserComment metadatum
+        exifData.add(key, &value);
+        pos = exifData.findKey(key);
+    }
+
+    // Now we should have a valid iterator in any case. We use the metadatum
+    // output operator to print the formatted value
+    std::cout << "Writing user comment '" << *pos << "' back to the image\n";
+
+    rc = exifData.write(argv[1]);
+    if (rc) {
+        std::string error = writeError(rc, argv[1]);
+        throw Exiv2::Error(error);
+    }
+
+   return rc;
+}
+catch (Exiv2::Error& e) {
+    std::cout << "Caught Exiv2 exception '" << e << "'\n";
+    return -1;
+}
+
+// *****************************************************************************
+// local definitions
+
+std::string readError(int rc, const std::string& path)
+{
+    std::string error;
+    switch (rc) {
+    case -1:
+        error = path + ": Failed to open the file";
+        break;
+    case -2:
+        error = path + ": The file contains data of an unknown image type";
+        break;
+    case 1:
+        error = path + ": Couldn't read from the input stream";
+        break;
+    case 2:
+        error = path + ": This does not look like a JPEG image";
+        break;
+    case 3:
+        error = path + ": No Exif data found in the file";
+        break;
+    case -99:
+        error = path + ": Unsupported Exif or GPS data found in IFD 1";
+        break;
+    default:
+        error = path + ": Reading Exif data failed, rc = " + Exiv2::toString(rc);
+        break;
+    }
+    return error;
+} // exifReadError
+
+std::string writeError(int rc, const std::string& path)
+{
+    std::string error;
+    switch (rc) {
+    case -1:
+        error = path + ": Failed to open the file";
+        break;
+    case -2:
+        error = path + ": The file contains data of an unknown image type";
+        break;
+    case -3:
+        error = path + ": Couldn't open temporary file";
+        break;
+    case -4:
+        error = path + ": Renaming temporary file failed";
+        break;
+    case 1:
+        error = path + ": Couldn't read from the input stream";
+        break;
+    case 2:
+        error = path + ": This does not look like a JPEG image";
+        break;
+    case 3:
+        error = path + ": No JFIF APP0 or Exif APP1 segment found in the file";
+        break;
+    case 4:
+        error = path + ": Writing to the output stream failed";
+        break;
+    default:
+        error = path + ": Reading Exif data failed, rc = " + Exiv2::toString(rc);
+        break;
+    }
+    return error;
+} // writeError