c – 内部类型作为模板参数

发布时间：2020-12-16 03:23:38 所属栏目：百科来源：网络整理

导读：ISO 98/03标准(第14.3.1节)似乎禁止使用具有内部链接的类型作为模板参数. (参见下面的示例.)C 11标准没有. G – 使用旧标准 – 允许它. 我是在误读03标准,还是只是让这张幻灯片？ namespace{ struct hidden { };}templatetypename Tstruct S{ T t;};int main

ISO 98/03标准(第14.3.1节)似乎禁止使用具有内部链接的类型作为模板参数. (参见下面的示例.)C 11标准没有.
G – 使用旧标准 – 允许它.
我是在误读03标准,还是只是让这张幻灯片？

namespace
{
    struct hidden { };
}

template<typename T>
struct S
{
   T t;
};

int main()
{
    S<hidden> s;
    return 0;
}

解决方法

你是正确的,C 03不允许使用具有内部链接的类型作为模板类型参数,而C 11则允许.

然而,我似乎记得,匿名命名空间内的定义仍然具有外部链接.

是的,第3.5节[basic.link]说

A name having namespace scope (3.3.5) has internal linkage if it is the name of

an object,reference,function or function template that is explicitly declared static or,

an object or reference that is explicitly declared const and neither explicitly declared extern nor previously declared to have external linkage; or

a data member of an anonymous union.

A name having namespace scope has external linkage if it is the name of

an object or reference,unless it has internal linkage; or

a function,unless it has internal linkage; or

a named class (clause 9),or an unnamed class defined in a typedef declaration in which the class has the typedef name for linkage purposes (7.1.3); or

a named enumeration (7.2),or an unnamed enumeration defined in a typedef declaration in which the enumeration has the typedef name for linkage purposes (7.1.3); or

an enumerator belonging to an enumeration with external linkage; or

a template,unless it is a function template that has internal linkage (clause 14); or

a namespace (7.3),unless it is declared within an unnamed namespace.

您在命名空间范围内有一个命名类,它具有外部链接.

ISO / IEC 14882：2003第115页底部的脚注阐明：

Although entities in an unnamed namespace might have external linkage,they are effectively qualified by a name unique to their translation unit and therefore can never be seen from any other translation unit.

如果您有其他版本,请尝试查看第7.3.1.1节[namespace.unnamed]

（编辑：李大同）

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