用于基本数据类型之间的转换，如把int转换成char，把int转换成enum。这种转换的安全性也要开发人员来保证。
把空指针转换成目标类型的空指针。
把任何类型的表达式转换成void类型。,Between the basic data types for conversion, such as the int into a char, the int to convert enum. This conversion should be the development of security personnel to ensure that. The null pointer into the target type of a null pointer. Any type of expression to convert type void.