t="_blank">System<span id="LST2463395C_2"></span><script type="text/javascript">AddLanguageSpecificTextSet("LST2463395C_2?cs=.|vb=.|cpp=::|nu=.|fs=.");</script>String</a><br /></dd><dt><span class="parameter">safe</span> (Optional)</dt><dd>类型：<a href="https://docs.microsoft.com/dotnet/api/system.nullable-1" target="_blank">System<span id="LST2463395C_3"></span><script type="text/javascript">AddLanguageSpecificTextSet("LST2463395C_3?cs=.|vb=.|cpp=::|nu=.|fs=.");</script>Nullable</a><span id="LST2463395