Unique Identifier for sent messages in good programming practice - c++

Question

A system send xml warning messages. To put the xml file together, a class was created so the warning could be generated before translating it to xml. Each message has to have an unique ID.
How unique? The IDs go from 3400 until 3500. If maximum is reached, the ID is reset.
#ifndef WARNINGMESSAGE_H
#define WARNINGMESSAGE_H
#include <ctime>
static unsigned int control_ID = 3399;
//Effect Codes:
const unsigned int TRAFFIC_FREE = 2;
//(...)
class WarningMessage{
public:
//setters
void setActionID();
//getters
//(...)
private:
unsigned int actionID; //to be controlled by control_ID
};
#endif // WARNINGPARAMVEHICLE_H
And in the cpp file, when the id of a message needs to be setted, the following is executed:
#include "project/include/warningmessage.h"
//setters
void WarningParamVehicle::setActionID(){
if(control_ID == 3500){
control_ID = 3399;
}
control_ID++;
actionID = control_ID;
}
Another detail that is important, the space in memory for this class message is given just once. Every time another message has to be sent, the instance is deleted and re-created as such:
void WarningDetector::createWarning(){
delete currentWarningMessage; // delete previous warning instance
currentWarningMessage = new WarningMessage();
(...)
}
and lastly, currentWarningMessage was declared in warning detector as a pointer:
WarningMessage* currentWarningMessage;
I can notice the bad programming practice in declaring the variable control_ID in the header file and outside of the class scope, however, given scenario coding like this look optimized. Is there a better way to solve this unique identifier problem seen here? Thanks a lot in advance

Answer 1

Good programming practice could include single responsibilities. For instance, setting the action id for the current message could be decoupled from deciding on the action id for the next message. This could enable consistent behavior when exceptions happen during the construction of a WarningMessage (if you get a chance to fix the cause of the exception you might want to try again to create the WarningMessage and expect the same actionId).
To address that and the other comments above you could for instance:
make control_ID a private static member of WarningMessage (setActionID is currently a member of WarningMessage)
remove the public setter setActionID and initialize actionID in the initialization list instead
manage control_ID, last thing inside the constructor (in case there are exceptions)
In the header:
#ifndef WARNINGMESSAGE_H
#define WARNINGMESSAGE_H
#include <ctime>
//Effect Codes:
const unsigned int TRAFFIC_FREE = 2;
//(...)
class WarningMessage{
public:
WarningMessage();
//remove public setters if your use case doesn't require them
//getters
//(...)
private:
// deconstructing control_ID
static const unsigned ID_COUNT = 100;
static const unsigned ID_START = 3400;
static unsigned idOffset = 0;
const unsigned int actionID; //to be controlled by control_ID
};
#endif // WARNINGPARAMVEHICLE_H
And in the cpp file:
#include "project/include/warningmessage.h"
unsigned WarningMessage::idOffset = 0;
WarningMessage::WarningMessage()
: actionId(ID_START + idOffset) /* ... */
{
// increment idOffset only when you are sure that it is safe
++idOffset;
idOffset %= ID_COUNT;
}
Note that this is not going to work in a multi-threaded environment, but that doesn't seem to be your concern at the moment

Answer 2

I would create 2 constants IDMIN = 3499 and IDMAX = 3500 to avoid having magic numbers in an implementation file. Those constants should be static const members of class WarningMessage.
I would set control_ID as a static variable in the method WarningParamVehicle::setActionID (isn't it WarningMessage::setActionID ?). It would then give :
class WarningMessage{
public:
static const int IDMIN = 3499;
static const int IDMAX = 3500;
//setters
void setActionID();
...
and later in implementation :
void WarningParamVehicle::setActionID(){
static int control_ID = WarningMessage::IDMIN;
if(control_ID == IDMAX){
control_ID = IDMIN;
}
control_ID++;
actionID = control_ID;
}