not compatible with Snopt 7.6 (Latest version) about ifopt HOT 1 CLOSED

Thanks for letting me know. I would not create a new branch, but treat the new SNOPT interface as a 3rd separate solver and therefore implement a new class "SnoptAdapter76" (snopt_adapter_76.h and snopt_adapter_76.cc ). The only additional element that must be adapted is then the CMakeLists.txt that must know which SNOPT version to link against which SNOPT adapter class.

This then allows the user after defining the entire problem to decide whether to solve it with IPOPT, SNOPT or the new version of SNOPT:
IpoptAdapter::Solve(nlp); // or SnoptAdapter::Solve(nlp) or SnoptAdapter76::Solve(nlp)

from ifopt.