ILOG CPLEX C++ API 9.0 Reference Manual

IloCplex::CallbackI
You do not create instances of this class; rather, you use one of its child classes to
implement your own callback. In order to implement your user-written callbacks with an
instance of IloCplex, you should follow these steps:
◆
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Determine which kind of callback you want to write, and choose the appropriate
class for it. The class hierarchy in Tree may give you some ideas here.
Derive your own subclass, MyCallbackI, say, from the appropriate predefined
callback class.
In your subclass of the callback class, use the protected API defined in the base
class to implement the main routine of your user-written callback. (All constructors
of predefined callback classes are protected; they can be called only from userwritten
derived subclasses.)
◆ In your subclass, implement the method duplicateCallback.
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Write a function myCallback, say, that creates an instance of your
implementation class in the Concert Technology environment and returns it as an
IloCplex::Callback handle.
Create an instance of your callback class and pass it to the member function use.
Note: Macros ILOXXXCALLBACKn (for n from 0 to 7) are available to facilitate
steps 2 through 5, where XXX stands for the particular callback under construction
and n stands for the number of parameters that the function written in step 5 is to
receive in addition to the environment parameter.
You can use one instance of a callback with only one instance of IloCplex. When you
use a callback with a second instance of IloCplex, a copy will be automatically
created using the method duplicateCallback, and that copy will be used instead.
Also, an instance of IloCplex takes account of only one instance of a particular
callback at any given time. That is, if you call use more than once with the same class
of callback, the last call overrides any previous one. For example, you can use only one
primal simplex callback at a time, or you can use only one network callback at a time;
and so forth.
There are two varieties of callbacks:
◆ Query callbacks enable your application to retrieve information about the current
solution in an instance of IloCplex. The information available depends on the
algorithm (primal simplex, dual simplex, barrier, mixed integer, or network) that you
are using. For example, a query callback can return the current objective value, the
number of simplex iterations that have been completed, and other details. Query
ILOG CPLEX C++ API 9.0 REFERENCE M ANUAL 99