哪个solrconfig.xml文件呢？(which solrconfig.xml file is it?)

 函数指针可以指向具有相同参数和返回类型的任何函数。 在上面的代码中，“bar”是一个指针， bar=&print表示让bar指向print 。 但是，一个函数不能=一个函数。 
 对函数指针有用的是，只要函数具有相同的参数和返回类型，它就可以指向ANY函数。 当函数指针用作另一个函数的参数时，这证明非常有用。 
 当函数用作参数时，传递的真实内容是函数的ADDRESS。 函数不能被解除引用（即它不能作为函数传递）。 我不太清楚，但似乎你的foo和test是相同的。 

A function pointer can point to any function that has the same parameters and return type. In your codes above, "bar" is a pointer, and bar=&print means let bar point to print. However, a function cannot = a function. 
 What's good for a function pointer is that it can point to ANY function as long as the function has the same parameters and return type. This proves quite useful when a function pointer serves as a parameter of another function. 
 When function is used as an argument, the real thing that is passed is the ADDRESS of the function. A function cannot be passed dereferenced (i.e. it cannot be passed AS a function). I'm not quite clear, but it seems your implementations of foo and test are identical.