c++ - 为什么不允许使用此默认模板参数？

Question

我有以下类(class):

template <typename Type = void>
class AlignedMemory {
public:
    AlignedMemory(size_t alignment, size_t size)
        :   memptr_(0) {
        int iret(posix_memalign((void **)&memptr_, alignment, size));
        if (iret) throw system_error("posix_memalign");
    }
    virtual ~AlignedMemory() {
        free(memptr_);
    }
    operator Type *() const { return memptr_; }
    Type *operator->() const { return memptr_; }
    //operator Type &() { return *memptr_; }
    //Type &operator[](size_t index) const;
private:
    Type *memptr_;
};

并尝试像这样实例化一个自动变量:

AlignedMemory blah(512, 512);

这会产生以下错误:

src/cpfs/entry.cpp:438: error: missing template arguments before ‘blah’

我做错了什么？ void 不是允许的默认参数吗？

Answer 1

我认为你需要写:

AlignedMemory<> blah(512, 512);

参见 14.3 [temp.arg]/4:

When default template-arguments are used, a template-argument list can be empty. In that case the empty <> brackets shall still be used as the template-argument-list.