const Descriptor *desc = DescriptorPool::generated_pool()->FindMessageTypeByName(msg_name); assert(desc);
上述示例代码，desc结果为空。最后在github找到答案。
上面链接中给出的解答是
OK, finally I figured out that there is no black magic and it's just a linker problem, I compiled the proto sources into a static library, seems the linker automatically optimized out those objs not used when linking against the static library. I follow this thread and it fixes the problem
另外一个人提出的问题和得到的回答
Q:how to config on Visual Studio,when build a static library?
A:An alternative is to reference these protos types somewhere in your code so they don't get stripped by the linker.(意思就是在之前的代码中使用过这个proto)