“>”标记之前的预期主表达式

Question

我有这样的代码：

class Client2ServerProtocol {

};

class ProtocolHelper {
public:
    template<class ProtocolClass>
    int GetProtocolId() {
        return -1;
    }
};

template<> inline int
ProtocolHelper::GetProtocolId<Client2ServerProtocol>() {
    return 1;
}

template<typename PROTOCOL_HELPER>
class Dispatcher {
public:
    template<typename PROTOCOL_CLASS>
    void Subscribe(int msgId) {
        int protoId = helper.GetProtocolId<PROTOCOL_CLASS>();
        printf("Subscribe protoId %d, msgId %d", protoId, msgId);
    }
    PROTOCOL_HELPER helper;
};

int main() {
    Dispatcher<ProtocolHelper> dispatcher;
    dispatcher.Subscribe<Client2ServerProtocol>(1);
    return 0;
}

它在 MSVC 下成功编译（并工作），但 gcc 抱怨语法无效：

test.cc:23:56: error: expected primary-expression before ‘>’ token int protoId = helper.GetProtocolId();

test.cc:23:58: error: expected primary-expression before ‘)’ token

我做错了什么？ int protoId = helper.GetProtocolId();

Answer 1

你只需要加上template关键字来表示它跟在一个模板之后：

int protoId = helper.template GetProtocolId<PROTOCOL_CLASS>();
                     ^^^^^^^^

“>”标记之前的预期主表达式

expected primary-expression before ‘>’ token

c++

templates

generic-programming