无法迭代Poco :: Any的std :: map

Question

我有一个std :: Poco :: Any的地图,我正在尝试迭代并输出到流但我得到编译器错误.我的代码如下:

map<string, Poco::Any>::const_iterator it;
map<string, Poco::Any>::const_iterator end = _map.end();
map<string, Poco::Any>::const_iterator begin = _map.begin();
for(it = begin; it != end; ++it) {
    const std::type_info &type = it->second.type();

    // compile error here:
    os << "  " << it->first << " : " << Poco::RefAnyCast<type>(it->second) << endl;
}

该行有2个错误:

'type' cannot appear in a constant-expression
no matching function for call to 'RefAnyCast(Poco::Any&)'

更新:

我知道模板是编译时间,而type()是运行时因此不起作用.谢谢你强调这一点.此外,DynamicAny将无法工作,因为它只接受具有DynamicAnyHolder实现的类型,并不理想.我想对这些类型强加的唯一规则是它们有<<重载.

下面是我目前正在做的,在某种程度上工作,但只转储已知类型,这不是我想要的.

string toJson() const {
    ostringstream os;
    os << endl << "{" << endl;
    map<string, Poco::Any>::const_iterator end = _map.end();
    map<string, Poco::Any>::const_iterator begin = _map.begin();
    for(map<string, Poco::Any>::const_iterator it = begin; it != end; ++it) {
        const std::type_info &type = it->second.type();
        os << "  " << it->first << " : ";

        // ugly, is there a better way?
        if(type == typeid(int)) os << Poco::RefAnyCast<int>(it->second);
        else if(type == typeid(float)) os << Poco::RefAnyCast<float>(it->second);
        else if(type == typeid(char)) os << Poco::RefAnyCast<char>(it->second);
        else if(type == typeid(string)) os << Poco::RefAnyCast<string>(it->second);
        else if(type == typeid(ofPoint)) os << Poco::RefAnyCast<ofPoint>(it->second);
        else if(type == typeid(ofVec2f)) os << Poco::RefAnyCast<ofVec2f>(it->second);
        else if(type == typeid(ofVec3f)) os << Poco::RefAnyCast<ofVec3f>(it->second);
        //else if(type == typeid(ofDictionary)) os << Poco::RefAnyCast<ofDictionary>(it->second);
        else os << "unknown type";

        os << endl;
    }
    os<< "}" << endl;
    return os.str();
}

Answer 1

运行时类型信息不能用于实例化模板.type_info只有在运行程序时才知道其值的实例,并不会奇怪地变成类似的类型int,std::string或者struct FooBar当编译器正在编译此代码时.

我不知道Poco库,但也许你可以使用他们的其他Any类型,DynamicAny(参见文档),希望你可以将存储的值转换std::string为输出:

os << "  " << it->first << " : " << it->second.convert<std::string>() << endl;