undefined reference to `typeinfo for IA' collect2: ld returned 1 exit status
背景：
c++工程，虚函数，继承，接口，代码如下：
classIA{
public:
virtualvoidprinta();
};
classCA:publicIA{
public:
CA(inta){
this->a=a;
}
~CA(){}
public:
voidprinta(){
printf("a=%d\n",a);
}
private:
inta;
};
intmain(int