void write(const std::string& file, Exiv2::ExifData& ed)
{
int rc = ed.write(file);
if (rc) {
std::string error = Exiv2::ExifData::strError(rc, file);
throw Exiv2::Error(error);
}
}
// *****************************************************************************
// 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 = Exiv2::ExifData::strError(rc, argv[1]);
throw Exiv2::Error(error);
}
/*
There are two pitfalls that we need to consider when setting the Exif user
comment (Exif.Photo.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(reinterpret_cast<const Exiv2::byte*>((charset + comment).data()),
8 + static_cast<long>(comment.size()));
// Set the Exif comment
Exiv2::ExifKey key("Exif.Photo.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 = Exiv2::ExifData::strError(rc, argv[1]);
throw Exiv2::Error(error);
}
return rc;
}
catch (Exiv2::Error& e) {
std::cout << "Caught Exiv2 exception '" << e << "'\n";
return -1;
}
// *****************************************************************************
// Main
int main()
try {
// Container for all metadata
Exiv2::ExifData exifData;
// *************************************************************************
// Add to the Exif data
// Create a ASCII string value (note the use of create)
Exiv2::Value* v = Exiv2::Value::create(Exiv2::asciiString);
// Set the value to a string
v->read("1999:12:31 23:59:59");
// Add the value together with its key to the Exif data container
Exiv2::ExifKey key("Exif.Photo.DateTimeOriginal");
exifData.add(key, v);
std::cout << "Added key \"" << key << "\", value \"" << *v << "\"\n";
// Delete the memory allocated by Value::create
delete v;
// Now create a more interesting value (without using the create method)
Exiv2::URationalValue* rv = new Exiv2::URationalValue;
// Set two rational components from a string
rv->read("1/2 1/3");
// Add more elements through the extended interface of rational value
rv->value_.push_back(std::make_pair(2,3));
rv->value_.push_back(std::make_pair(3,4));
// Add the key and value pair to the Exif data
key = Exiv2::ExifKey("Exif.Image.PrimaryChromaticities");
exifData.add(key, rv);
std::cout << "Added key \"" << key << "\", value \"" << *rv << "\"\n";
// Delete memory allocated on the heap
delete rv;
// *************************************************************************
// Modify Exif data
// Find the timestamp metadatum by its key
key = Exiv2::ExifKey("Exif.Photo.DateTimeOriginal");
Exiv2::ExifData::iterator pos = exifData.findKey(key);
if (pos == exifData.end()) throw Exiv2::Error("Key not found");
// Modify the value
std::string date = pos->toString();
date.replace(0,4,"2000");
pos->setValue(date);
std::cout << "Modified key \"" << key
<< "\", new value \"" << pos->value() << "\"\n";
// Find the other key
key = Exiv2::ExifKey("Exif.Image.PrimaryChromaticities");
pos = exifData.findKey(key);
if (pos == exifData.end()) throw Exiv2::Error("Key not found");
// Get a pointer to a copy of the value
v = pos->getValue();
// Downcast the Value pointer to its actual type
rv = dynamic_cast<Exiv2::URationalValue*>(v);
if (rv == 0) throw Exiv2::Error("Downcast failed");
// Modify the value directly through the interface of URationalValue
rv->value_[2] = std::make_pair(88,77);
// Copy the modified value back to the metadatum
pos->setValue(rv);
// Delete the memory allocated by getValue
delete v;
std::cout << "Modified key \"" << key
<< "\", new value \"" << pos->value() << "\"\n";
// *************************************************************************
// Delete metadata from the Exif data container
// Delete the metadatum at iterator position pos
key = Exiv2::ExifKey("Exif.Image.PrimaryChromaticities");
pos = exifData.findKey(key);
if (pos == exifData.end()) throw Exiv2::Error("Key not found");
exifData.erase(pos);
std::cout << "Deleted key \"" << key << "\"\n";
// *************************************************************************
// Finally, write the remaining Exif data to an image file
int rc = exifData.write("img_2158.jpg");
if (rc) {
std::string error = Exiv2::ExifData::strError(rc, "img_2158.jpg");
throw Exiv2::Error(error);
}
return 0;
}
catch (Exiv2::Error& e) {
std::cout << "Caught Exiv2 exception '" << e << "'\n";
return -1;
}
