[英]Why is this default template parameter not allowed?
I have the following class: 我有以下课程:
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_;
};
And attempt to instantiate an automatic variable like this: 并尝试实例化一个自动变量,如下所示:
AlignedMemory blah(512, 512);
This gives the following error: 这会出现以下错误:
src/cpfs/entry.cpp:438: error: missing template arguments before 'blah'
src / cpfs / entry.cpp:438:错误:'blah'之前缺少模板参数
What am I doing wrong? 我究竟做错了什么? Is
void
not an allowed default parameter? void
不是允许的默认参数吗?
I think that you need to write: 我想你需要写:
AlignedMemory<> blah(512, 512);
See 14.3 [temp.arg] / 4: 见14.3 [temp.arg] / 4:
When default template-arguments are used, a template-argument list can be empty.
使用默认模板参数时 , 模板参数列表可以为空。 In that case the empty
<>
brackets shall still be used as the template-argument-list .在这种情况下,空
<>
括号仍应用作模板参数列表 。
Your syntax is wrong: 你的语法错了:
AlignedMemory blah(512, 512); //wrong syntax
Correct syntax is this: 正确的语法是这样的:
AlignedMemory<> blah(512, 512); //this uses "void" as default type!
The error message itself gives this hint. 错误消息本身给出了这个提示。 Look at it again:
再看一遍:
src/cpfs/entry.cpp:438: error: missing template arguments before 'buf'
src / cpfs / entry.cpp:438:错误:'buf' 之前 缺少模板参数
PS: I'm sure 'buf' is a typo. PS:我确定'buf'是一个错字。 You wanted to write 'blah' - the name of your variable!
你想写'blah' - 变量的名字!
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