我们可以有一个匿名结构作为模板参数吗？ [英] Can we have an anonymous struct as template argument?

问题描述

标题是不言而喻的，但这里有一个简单的例子：

The title is pretty self-explanatory, but here's a simplified example:

#include <cstdio>

template <typename T>
struct MyTemplate {

    T member;

    void printMemberSize() {
        printf("%i\n", sizeof(T));
    }

};

int main() {

    MyTemplate<struct { int a; int b; }> t; // <-- compiler doesn't like this

    t.printMemberSize();

    return 0;

}

编译器在我尝试使用匿名结构时模板参数。

The compiler complains when I try to use an anonymous struct as a template argument. What's the best way to achieve something like this without having to have a separate, named struct definition?

推荐答案

不允许使用一个单独的命名结构定义，在C ++ 03或甚至C ++ 0x中将未命名的类型定义为模板参数。

You are not allowed to define an unnamed type as a template argument in C++03 or even in C++0x.

最好的做法是创建一个命名的struct local main（在C ++ 0x ¹ ）

The best you can do it to create a named struct local to main (in C++0x¹)

_{1：不允许使用本地类型作为模板参数在C ++ 03，但C ++ 0x允许它。}

也检查缺陷报告在这里。建议的解决方案提到

Also check out the Defect Report here. The proposed solution mentions

以下类型不能用作模板类型参数的模板参数：

The following types shall not be used as a template-argument for a template type-parameter:

• 其名称没有链接的类型


• 没有链接名称的未命名类或枚举类型




通过将声明符运算符应用于此列表中的某个类型创建的类型

• 使用此列表中某个类型的函数类型

• a type whose name has no linkage
• an unnamed class or enumeration type that has no name for linkage purposes (7.1.3 [dcl.typedef])
• a cv-qualified version of one of the types in this list
• a type created by application of declarator operators to one of the types in this list
• a function type that uses one of the types in this list

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编译器在我尝试使用匿名结构时模板参数。

The compiler complains when I try to use an anonymous struct as a template parameter.

您是不是指模板参数？模板参数与模板参数不同。

Did you mean template argument? Template parameter is different from template argument.

例如

template < typename T > // T is template parameter
class demo {};

int main()
{
   demo <int> x; // int is template argument
}

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