Difference between revisions of "Serializing and deserializing root objects"
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ROOT objects can be serialized to a byte array or reconstructed from the byte array quite easily. One reason to do this might | ROOT objects can be serialized to a byte array or reconstructed from the byte array quite easily. One reason to do this might | ||
be to store or transport ROOT objects in a way not supported by ROOT itself. An example is transport of a ROOT histogram from a producer to a | be to store or transport ROOT objects in a way not supported by ROOT itself. An example is transport of a ROOT histogram from a producer to a | ||
| − | consumer program via the cMsg package, a publish/subscribe messaging system that will be used extensively in the Hall D online monitoring system (see | + | consumer program via the cMsg package, a publish/subscribe messaging system that will be used extensively in the Hall D online monitoring system (see Example Programs below). |
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===Deserialize=== | ===Deserialize=== | ||
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| + | Deserializing involves a trick due to limitations of the TMessage class. The required constructor is protected, so a covering class must be created to expose it: | ||
| + | |||
| + | <pre> | ||
| + | // class needed to expose protected TMessage constructor | ||
| + | class MyTMessage : public TMessage { | ||
| + | public: | ||
| + | MyTMessage(void *buf, Int_t len) : TMessage(buf, len) { } | ||
| + | }; | ||
| + | </pre> | ||
| + | |||
| + | |||
| + | |||
Revision as of 14:28, 30 June 2009
Introduction
ROOT objects can be serialized to a byte array or reconstructed from the byte array quite easily. One reason to do this might be to store or transport ROOT objects in a way not supported by ROOT itself. An example is transport of a ROOT histogram from a producer to a consumer program via the cMsg package, a publish/subscribe messaging system that will be used extensively in the Hall D online monitoring system (see Example Programs below).
Serialize
ROOT TMessage objects can hold serialized ROOT objects. They are filled via the write() method:
#include "TMessage.h" // create TMessage object capable of holding serialized ROOT object TMessage *tm = new TMessage(kMESS_OBJECT); // fill with serialized version of some ROOT object tm->WriteObject(some_root_object); // get pointer to TMessage internal buffer and length char *buffer = tm->Buffer(); int bufferLength = tm->Length()); // in bytes
Deserialize
Deserializing involves a trick due to limitations of the TMessage class. The required constructor is protected, so a covering class must be created to expose it:
// class needed to expose protected TMessage constructor
class MyTMessage : public TMessage {
public:
MyTMessage(void *buf, Int_t len) : TMessage(buf, len) { }
};
Example Programs
cMsgRootProducer.cc,cMsgRootConsumer.cc,Makefile Examples demonstrate transport via cMsg package.
