c++ - protobuf：new Prototype() 和 Prototype.Clear() 之间的区别

Question

对于两段代码

for (loop) {
    ProtoType instance;
    // do something with instance;
}

/* --------------- */

ProtoType instance;
for (loop) {
    // do something with instance;
    instance.Clear();
}

我得到了后者的核心转储。那么这两段代码有什么区别呢？Prototype.Clear() 真正做什么？