Originally posted by: Laser.Cho

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inline IloIntExprArg IloLengthOf(const IloIntervalVar a, IloInt absVal =0){
  IloAssert(a.getImpl(), "IloIntervalVar: empty handle.");
  return a._makeLengthExpr(a.getEnv(),absVal);
}

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this is one of the given function from concert, in the ilosmodel.h.

and it is used like this

-===========================

ilointervalvar movingVar;

_model.add(TimeVar >= IloPresenceOf(_env, movingVar) * IloLengthOf(movingVar));

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what is the function of "IloLengthOf" or "_makeLengthExpr" ?

As I understand(it can be incorrect)

the example what i mentioned is meaning 

" If movingvar is exist, then the length of movingvar is smaller than timevar. "

so, "ilolengthof" means doing return value length of intervalvar. <- Am I right?

Originally posted by: PhilippeLaborie

Indeed. But may I suggest that you look at the documentation rather than in the header files, things would be clearer this way.

Here is what the documentaion of IloLengthOf says (see https://www.ibm.com/support/knowledgecenter/SSSA5P_12.7.1/ilog.odms.cpo.help/refcppcpoptimizer/html/functions/IloLengthOf.html):

IloLengthOf
public IloIntExprArg IloLengthOf(const IloIntervalVar a, IloInt absVal=0)
Definition file: ilconcert/ilosmodel.h
Returns an expression representing the length of the interval variable.
This function returns an integer expression that represents the length of interval variable a whenever the interval variable is present. When the interval variable is absent, it returns the constant integer value absVal (by default: 0).
For more information on expressions on interval variables, see the concept Expressions over Interval Variables.