如何设置一个boost ::可选回到未初始化的状态？

如何“重置”/“取消”一个boost::optional ？

 optional<int> x; if( x ) { // We won't hit this since x is uninitialized } x = 3; if( x ) { // Now we will hit this since x has been initialized } // What should I do here to bring x back to uninitialized state? if( x ) { // I don't want to hit this } 

Answer 1

 x = boost::none; 

Answer 2

一个简单的方法是：

 x = optional<int>(); //reset to default 

或者干脆：

 x.reset(); 

它破坏当前值，保留这个未初始化（默认）。