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Iterating through bagfile messages yields nullpointer

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Hi, I wrote the following class that iterates through the messages of a bagfile: BagReader.h: class BagReader { public: BagReader(std::string const &filename); ~BagReader(); void addTopic(std::string const &name); void readNextMessage(); template boost::shared_ptr getMessage() { if (!view) { view.reset(new rosbag::View(*bag, rosbag::TopicQuery(topics))); messageIterator = view->begin(); } // The instantiation of the message will be a smart pointer. boost::shared_ptr ptr = messageIterator->instantiate(); return ptr; } private: boost::scoped_ptr bag; boost::scoped_ptr view; rosbag::View::iterator messageIterator; std::vector topics; }; BagReader.cpp: #include "BagReader.h" BagReader::BagReader(std::string const &filename) : bag(new rosbag::Bag(filename)) { } BagReader::~BagReader() { bag->close(); } void BagReader::addTopic(std::string const &name) { topics.push_back(name); } void BagReader::readNextMessage() { if (messageIterator != view->end()) ++messageIterator; else messageIterator = view->begin(); } Now I initialize my reader giving it the path to a bagfile and adding the two topics i want to read from: std::string const &path = bagfilesDirectory + "/dice_detection.bag"; bagReader.reset(new BagReader(path)); bagReader->addTopic("/camera/depth_registered/points"); bagReader->addTopic("/tf"); Then I do the following to iterate through the messages of the bagfile: sensor_msgs::PointCloud2ConstPtr cloud = bagReader->getMessage(); // Do something with the cloud... bagReader->readNextMessage(); Now my problem is, that ptr is set to NULL and I don't know why. I roughly followed [this](http://wiki.ros.org/rosbag/Code%20API#cpp_api) tutorial.

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