Defines whether Checked Iterators are enabled. If defined as 1, unsafe iterator use causes a runtime error. If defined as 0, checked iterators are disabled. The exact behavior of the runtime error depends on the value of _SECURE_SCL_THROWS. In debug mode, the default value for _SECURE_SCL is 1, meaning checked iterators are enabled. In release mode, the default value for _SECURE_SCL is 0.