In the Callable Library, ILOG CPLEX defines a few special data types for specific ILOG CPLEX objects, as you see in Table 3.1. The types starting with CPXC represent the corresponding pointers to constant (const) objects

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When any of these special variables are set to a value returned by an appropriate routine, that value can be passed directly to other ILOG CPLEX routines that require such parameters. The actual internal type of these variables is a memory address (that is, a pointer); this address uniquely identifies the corresponding object. If you are programming in a language other than C, you should choose an appropriate integer type or pointer type to hold the values of these variables.