Function cnlp_open_output_file 

pub unsafe extern "C" fn cnlp_open_output_file(
    problem: CNLP_ProblemPtr,
    file_name: *const c_char,
    print_level: CNLP_Int,
) -> CNLP_Bool

Function for opening an output file for a given name with given printlevel. Returns 0 if there was a problem opening the file.