Sample usage of high-level XMP classes.

// SPDX-License-Identifier: GPL-2.0-or-later
// Sample/test for high level XMP classes. See also addmoddel.cpp
#include <exiv2/exiv2.hpp>
#include <cassert>
#include <cmath>
#include <iostream>
bool isEqual(float a, float b) {
double d = std::fabs(a - b);
return d < 0.00001;
int main() try {
// The XMP property container
Exiv2::XmpData xmpData;
// -------------------------------------------------------------------------
// Teaser: Setting XMP properties doesn't get much easier than this:
xmpData["Xmp.dc.source"] = "xmpsample.cpp"; // a simple text value
xmpData["Xmp.dc.subject"] = "Palmtree"; // an array item
xmpData["Xmp.dc.subject"] = "Rubbertree"; // add a 2nd array item
// a language alternative with two entries and without default
xmpData["Xmp.dc.title"] = "lang=de-DE Sonnenuntergang am Strand";
xmpData["Xmp.dc.title"] = "lang=en-US Sunset on the beach";
// -------------------------------------------------------------------------
// Any properties can be set provided the namespace is known. Values of any
// type can be assigned to an Xmpdatum, if they have an output operator. The
// default XMP value type for unknown properties is a simple text value.
xmpData["Xmp.dc.one"] = -1;
xmpData["Xmp.dc.two"] = 3.1415;
xmpData["Xmp.dc.three"] = Exiv2::Rational(5, 7);
xmpData["Xmp.dc.four"] = static_cast<uint16_t>(255);
xmpData["Xmp.dc.five"] = 256;
xmpData["Xmp.dc.six"] = false;
// In addition, there is a dedicated assignment operator for Exiv2::Value
Exiv2::XmpTextValue val("Seven");
xmpData["Xmp.dc.seven"] = val;
xmpData["Xmp.dc.eight"] = true;
// Extracting values
assert(xmpData["Xmp.dc.one"].toInt64() == -1);
[[maybe_unused]] const Exiv2::Value& getv1 = xmpData["Xmp.dc.one"].value();
assert(isEqual(getv1.toFloat(), -1));
assert(getv1.toRational() == Exiv2::Rational(-1, 1));
[[maybe_unused]] const Exiv2::Value& getv2 = xmpData["Xmp.dc.two"].value();
assert(isEqual(getv2.toFloat(), 3.1415f));
assert(getv2.toInt64() == 3);
[[maybe_unused]] Exiv2::Rational R = getv2.toRational();
assert(isEqual(static_cast<float>(R.first) / R.second, 3.1415f));
[[maybe_unused]] const Exiv2::Value& getv3 = xmpData["Xmp.dc.three"].value();
assert(isEqual(getv3.toFloat(), 5.0f / 7.0f));
assert(getv3.toInt64() == 0); // long(5.0 / 7.0)
assert(getv3.toRational() == Exiv2::Rational(5, 7));
[[maybe_unused]] const Exiv2::Value& getv6 = xmpData["Xmp.dc.six"].value();
assert(getv6.toInt64() == 0);
assert(getv6.toFloat() == 0.0f);
assert(getv6.toRational() == Exiv2::Rational(0, 1));
const Exiv2::Value& getv7 = xmpData["Xmp.dc.seven"].value();
getv7.toInt64(); // this should fail
[[maybe_unused]] const Exiv2::Value& getv8 = xmpData["Xmp.dc.eight"].value();
assert(getv8.toInt64() == 1);
assert(getv8.toFloat() == 1.0f);
assert(getv8.toRational() == Exiv2::Rational(1, 1));
// Deleting an XMP property
auto pos = xmpData.findKey(Exiv2::XmpKey("Xmp.dc.eight"));
if (pos == xmpData.end())
throw Exiv2::Error(Exiv2::ErrorCode::kerErrorMessage, "Key not found");
// -------------------------------------------------------------------------
// Exiv2 has specialized values for simple XMP properties, arrays of simple
// properties and language alternatives.
// Add a simple XMP property in a known namespace
xmpData.add(Exiv2::XmpKey("Xmp.dc.format"), v.get());
// Add an ordered array of text values.
v = Exiv2::Value::create(Exiv2::xmpSeq); // or xmpBag or xmpAlt.
v->read("1) The first creator"); // The sequence in which the array
v->read("2) The second creator"); // elements are added is their
v->read("3) And another one"); // order in the array.
xmpData.add(Exiv2::XmpKey("Xmp.dc.creator"), v.get());
// Add a language alternative property
v->read("lang=de-DE Hallo, Welt"); // The default doesn't need a
v->read("Hello, World"); // qualifier
xmpData.add(Exiv2::XmpKey("Xmp.dc.description"), v.get());
// According to the XMP specification, Xmp.tiff.ImageDescription is an
// alias for Xmp.dc.description. Exiv2 treats an alias just like any
// other property and leaves it to the application to implement specific
// behaviour if desired.
xmpData["Xmp.tiff.ImageDescription"] = "TIFF image description";
xmpData["Xmp.tiff.ImageDescription"] = "lang=de-DE TIFF Bildbeschreibung";
// -------------------------------------------------------------------------
// Register a namespace which Exiv2 doesn't know yet. This is only needed
// when properties are added manually. If the XMP metadata is read from an
// image, namespaces are decoded and registered at the same time.
Exiv2::XmpProperties::registerNs("myNamespace/", "ns");
// -------------------------------------------------------------------------
// Add a property in the new custom namespace.
xmpData["Xmp.ns.myProperty"] = "myValue";
// -------------------------------------------------------------------------
// There are no specialized values for structures, qualifiers and nested
// types. However, these can be added by using an XmpTextValue and a path as
// the key.
// Add a structure
xmpData.add(Exiv2::XmpKey("Xmp.xmpDM.videoFrameSize/stDim:w"), &tv);
xmpData.add(Exiv2::XmpKey("Xmp.xmpDM.videoFrameSize/stDim:h"), &tv);
xmpData.add(Exiv2::XmpKey("Xmp.xmpDM.videoFrameSize/stDim:unit"), &tv);
// Add an element with a qualifier (using the namespace registered above)
xmpData["Xmp.dc.publisher"] = "James Bond"; // creates an unordered array
xmpData["Xmp.dc.publisher[1]/?ns:role"] = "secret agent";
// Add a qualifier to an array element of Xmp.dc.creator (added above)
xmpData.add(Exiv2::XmpKey("Xmp.dc.creator[2]/?ns:role"), &tv);
// Add an array of structures
tv.read(""); // Clear the value
xmpData.add(Exiv2::XmpKey("Xmp.xmpBJ.JobRef"), &tv); // Set the array type.
tv.read("Birthday party");
xmpData.add(Exiv2::XmpKey("Xmp.xmpBJ.JobRef[1]/stJob:name"), &tv);
xmpData.add(Exiv2::XmpKey("Xmp.xmpBJ.JobRef[1]/stJob:role"), &tv);
tv.read("Wedding ceremony");
xmpData.add(Exiv2::XmpKey("Xmp.xmpBJ.JobRef[2]/stJob:name"), &tv);
tv.read("Best man");
xmpData.add(Exiv2::XmpKey("Xmp.xmpBJ.JobRef[2]/stJob:role"), &tv);
// Add a creator contact info structure
xmpData["Xmp.iptc.CreatorContactInfo/Iptc4xmpCore:CiAdrCity"] = "Kuala Lumpur";
xmpData["Xmp.iptc.CreatorContactInfo/Iptc4xmpCore:CiAdrCtry"] = "Malaysia";
xmpData["Xmp.iptc.CreatorContactInfo/Iptc4xmpCore:CiUrlWork"] = "http://www.exiv2.org";
// -------------------------------------------------------------------------
// Output XMP properties
for (auto&& md : xmpData) {
std::cout << std::setfill(' ') << std::left << std::setw(44) << md.key() << " " << std::setw(9) << std::setfill(' ')
<< std::left << md.typeName() << " " << std::dec << std::setw(3) << std::setfill(' ') << std::right
<< md.count() << " " << std::dec << md.value() << std::endl;
// -------------------------------------------------------------------------
// Serialize the XMP data and output the XMP packet
std::string xmpPacket;
if (0 != Exiv2::XmpParser::encode(xmpPacket, xmpData)) {
throw Exiv2::Error(Exiv2::ErrorCode::kerErrorMessage, "Failed to serialize XMP data");
std::cout << xmpPacket << "\n";
// Cleanup
} catch (Exiv2::Error& e) {
std::cout << "Caught Exiv2 exception '" << e << "'\n";
Simple error class used for exceptions. An output operator is provided to print errors to a stream.
Definition: error.hpp:235
Common interface for all types of values used with metadata.
Definition: value.hpp:33
bool ok() const
Check the ok status indicator. After a to<Type> conversion, this indicator shows whether the conversi...
Definition: value.hpp:181
static UniquePtr create(TypeId typeId)
A (simple) factory to create a Value type.
virtual float toFloat(size_t n=0) const =0
Convert the n-th component of the value to a float. The behaviour of this method may be undefined if ...
virtual Rational toRational(size_t n=0) const =0
Convert the n-th component of the value to a Rational. The behaviour of this method may be undefined ...
virtual int64_t toInt64(size_t n=0) const =0
Convert the n-th component of the value to an int64_t. The behaviour of this method may be undefined ...
A container for XMP data. This is a top-level class of the Exiv2 library.
Definition: xmp_exiv2.hpp:138
iterator end()
End of the metadata.
long count() const
Get the number of metadata entries.
int add(const XmpKey &key, const Value *value)
Add an Xmpdatum from the supplied key and value pair. This method copies (clones) the value.
iterator findKey(const XmpKey &key)
Find the first Xmpdatum with the given key, return an iterator to it.
Concrete keys for XMP metadata.
Definition: properties.hpp:207
static void terminate()
Terminate the XMP Toolkit and unregister custom namespaces.
static int encode(std::string &xmpPacket, const XmpData &xmpData, uint16_t formatFlags=useCompactFormat, uint32_t padding=0)
Encode (serialize) XMP metadata from xmpData into a string xmpPacket. The XMP packet returned in the ...
static bool initialize(XmpParser::XmpLockFct xmpLockFct=nullptr, void *pLockData=nullptr)
Initialize the XMP Toolkit.
static void registerNs(const std::string &ns, const std::string &prefix)
Register namespace ns with preferred prefix prefix.
Value type suitable for simple XMP properties and XMP nodes of complex types which are not parsed int...
Definition: value.hpp:638
std::pair< int32_t, int32_t > Rational
8 byte signed rational type.
Definition: types.hpp:31
@ langAlt
XMP language alternative type.
Definition: types.hpp:96
@ xmpText
XMP text type.
Definition: types.hpp:92
@ xmpSeq
XMP sequence type.
Definition: types.hpp:95