相关疑难解决方法(0)

在模板,在那里,为什么我必须把typename和template上依赖的名字呢？究竟什么是依赖名称？我有以下代码:

template <typename T, typename Tail> // Tail will be a UnionNode too.
struct UnionNode : public Tail {
    // ...
    template<typename U> struct inUnion {
        // Q: where to add typename/template here?
        typedef Tail::inUnion<U> dummy; 
    };
    template< > struct inUnion<T> {
    };
};
template <typename T> // For the last node Tn.
struct UnionNode<T, void> {
    // ...
    template<typename U> struct inUnion {
        char fail[ -2 + (sizeof(U)%2) ]; // Cannot be instantiated for any …

我正在编写一些c ++模板代码来替换当前源中的if-else条件.在这里,我基于两个条件派生Helper数据类型,1.isAdvice 2. SimpleOrComplex

见下面的模板代码:

template<bool isAdvice, class SH, class CH>
class IfThenElse;

template<class SH, class CH>
class IfThenElse<true, SH, CH>
{
    public:
    typedef SH Helper;
};

template<class SH, class CH>
class IfThenElse<false, SH, CH>
{
    public:
    typedef CH Helper;
};

template <bool isAdvice, bool SimpleOrComplex>
class DeriveHelper
{
    public:
        typedef typename IfThenElse<isAdvice,
                 IfThenElse<SimpleOrComplex, SimpleHelper, ComplexHelper>::Helper,
                 IfThenElse<SimpleOrComplex, SimpleNoAdvHelper, ComplexNoAdvHelper>::Helper>::Helper DerivedHelper;


};

但是,在编译时获取此错误:

template.cpp:135: error: type/value mismatch at argument 2 in template parameter list for 'template<bool isTradeAdvice, class SH, class GH> …