What version of OR-Tools and what language are you using?
Version: v9.6
Language: C++

Which solver are you using (e.g. CP-SAT, Routing Solver, GLOP, BOP, Gurobi)
CPLEX 22.10

What operating system (Linux, Windows, ...) and version?
Ubuntu Linux 18.04

What did you do?

• I use the API to create a solver

  #define MIPSOLVER "CPLEX"
  solver = std::unique_ptr<ORTools::MPSolver>( ORTools::MPSolver::CreateSolver(MIPSOLVER) );

and add variables, constraints, and objective function.

• I can successfully write the model to a file

  std::string MIP;
  solver->ExportModelAsLpFormat(false,&MIP); 
  std::ofstream myfile;
  myfile.open ("MIP.lp");
  myfile << MIP;
  myfile.close();

and solve the problem using the interactive prompt of cplex.

• When I solve the problem programmtically, however, via

const ORTools::MPSolver::ResultStatus result_status = solver->Solve();

the check in

What did you expect to see

The solver should run without problem. It does so if I use

  #define MIPSOLVER "SCIP"
  solver = std::unique_ptr<ORTools::MPSolver>( ORTools::MPSolver::CreateSolver(MIPSOLVER) );

What did you see instead?

I got an error message like this

cplex_interface.cc:866
Check failed: last_variable_index_ == cols (0 vs. 450)

Anything else we should know about your project / environment

When I removed

At other places incplex_interface.cc the code can deal with last_variable_index_ being zero, e.g.

Possibly the root cause of the problem is here: