Check to make sure we have a valid db pointer. This test is not ** foolproof but it does provide some measure of protection against ** misuse of the interface such as passing in db pointers that are ** NULL or which have been previously closed. If this routine returns ** 1 it means that the db pointer is valid and 0 if it should not be ** dereferenced for any reason. The calling function should invoke ** SQLITE_MISUSE immediately. ** ** sqlite3SafetyCheckOk() requires that the db pointer be valid for ** use. sqlite3SafetyCheckSickOrOk() allows a db pointer that failed to ** open properly and is not fit for general use but which can be ** used as an argument to sqlite3_errmsg() or sqlite3_close().翻译

这段代码注释的作用是检查数据库指针是否有效。这个检测不是绝对可靠的，但它可以提供一定程度的保护，防止接口被误用，例如传递空指针或已经关闭的指针。如果这个函数返回1，表示数据库指针有效；如果返回0，表示不应该对其进行任何解引用操作。调用该函数的函数应立即调用SQLITE_MISUSE。sqlite3SafetyCheckOk()要求数据库指针有效使用，而sqlite3SafetyCheckSickOrOk()允许一个打开失败且不适合一般使用的数据库指针，但可以用作sqlite3_errmsg()或sqlite3_close()的参数。