Boost :: bind仅当未在构造函数中设置时，“对空boost :: function的调用"才会失败 [英] Boost::bind 'Call to empty boost::function' fails only if not set in constructor

问题描述

为什么除非从类的构造函数中调用，否则使用以下命令为什么会失败?

Why might using the following fail unless called from the constructor of the class?

    updateState = boost::bind( &PhysicsObject::updateActive, this );

但是，以下内容在运行时失败，并带有"what():对空boost :: function的调用"例外

However the following fails at runtime, with a 'what(): call to empty boost::function' exception

void PhysicsObject::setState( PhsyicsObjectState aState ) {
_state = aState;

if( _state == ACTIVE ) { // This branch is executed
    updateState = boost::bind( &PhysicsObject::updateActive, this );
} else {
    updateState = boost::bind( &PhysicsObject::updateExploding, *this );
}
}

推荐答案

调用未设置的boost::function会引发此类异常.您应该根据默认的状态"在构造函数中对其进行初始化，否则，如果setState传递的状态与当前状态相同，则不会设置它.

Calling a boost::function that wasn't set would raise such exception. You should initialize it in your constructor according to the default "state", otherwise your setState won't set it if passed a state same as the current.

请注意，在第二个绑定中，您正在传递>指向的对象的副本.

Note that in your second bind, you are passing a copy of the object pointed by this.

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