Exiv2加入键值对的几种方式

int main()
{
    // 方式1加入键值对
    Exiv2::ExifData exifData;
    exifData["Exif.Image.Model"] = "Test 1";                     // AsciiValue
    exifData["Exif.Image.SamplesPerPixel"] = uint16_t(162);      // UShortValue
    exifData["Exif.Image.XResolution"] = int32_t(-2);            // LongValue
    exifData["Exif.Image.YResolution"] = Exiv2::Rational(-2, 3); // RationalValue
    exifData["Exif.GPSInfo.GPSLongitude"] = Exiv2::Rational(50,20);; // RationalValue
    std::cout << "Added a few tags the quick way.\n";

    // 方式2加入键值对
    Exiv2::Value::AutoPtr v = Exiv2::Value::create(Exiv2::asciiString);
    v->read("1999:12:31 23:59:59");
    Exiv2::ExifKey key("Exif.Photo.DateTimeOriginal");
    exifData.add(key, v.get());
    std::cout << "Added key \"" << key << "\", value \"" << *v << "\"\n";

    // 方式3加入键值对
    Exiv2::URationalValue::AutoPtr rv(new Exiv2::URationalValue);
    rv->read("1/2 1/3");
    // 通过rational value的扩展接口添加更多元素
    rv->value_.push_back(std::make_pair(2, 3));
    rv->value_.push_back(std::make_pair(3, 4));
    // 将键值对添加到Exif数据
    key = Exiv2::ExifKey("Exif.Image.PrimaryChromaticities");
    exifData.add(key, rv.get());
    std::cout << "Added key \"" << key << "\", value \"" << *rv << "\"\n";

    // 方式4加入键值对
    // 既然我们知道元数据存在（或者如果不存在，我们不介意创建新标签），我们可以简单地这样做
    Exiv2::Exifdatum& tag = exifData["Exif.Photo.DateTimeOriginal"];
    std::string date = tag.toString();
    date.replace(0, 4, "2000");
    tag.setValue(date);
    std::cout << "Modified key \"" << tag.key() << "\", new value \"" << tag.value() << "\"\n";

    // 方式5加入键值对
    // 或者，我们可以使用findKey()
    key = Exiv2::ExifKey("Exif.Image.PrimaryChromaticities");
    Exiv2::ExifData::iterator pos = exifData.findKey(key);
    if (pos != exifData.end())
    {
        // 获取指向值副本的指针
        v = pos->getValue();
        // 将值指针向下投射到其实际类型
        Exiv2::URationalValue* prv = dynamic_cast<Exiv2::URationalValue*>(v.release());
        if (prv != 0)
        {
            rv = Exiv2::URationalValue::AutoPtr(prv);
            // 通过URationalValue接口直接修改值
            rv->value_[2] = std::make_pair(88, 77);
            // 将修改后的值复制回元基准
            pos->setValue(rv.get());
            std::cout << "Modified key \"" << key << "\", new value \"" << pos->value() << "\"\n";
        }
        else { std::cout << "Downcast failed"; }
    }
    else { std::cout << "Key not found"; }

     // 最后，将剩余的Exif数据写入图像文件
    const char imagePath[] = "./test.jpeg";
    Exiv2::Image::AutoPtr image = Exiv2::ImageFactory::open(imagePath);
    assert(image.get() != 0);
    image->setExifData(exifData);
    image->writeMetadata();

    system("pause");
    return 0;
}