The routine CPXsetbranchnosolncallbackfunc sets the callback function that will be called instead of the branch callback when there is a failure due to such situations as an iteration limit being reached, unboundedness being detected, numeric difficulties being encountered, while the node LP is being solved. In consequence of the failure, whether the node is feasible or infeasible cannot be known and thus CPLEX routines such as CPXsolution may fail. In this situation, CPLEX will attempt to fix some variables and continue.

These conditions are rare (except when the user has set a very low iteration limit), so it is acceptable to let CPLEX follow its default action in these cases.