c – MSVC中的模板静态定义和明确的专门化实例化错误

概述我想知道为什么以下代码在 gcc中运行正常 #include <iostream>using namespace std;template<typename T>struct F { static T const value;};template<> struct F<int> { // Specialization static int const value; 我想知道为什么以下代码在 gcc中运行正常

#include <iostream>using namespace std;template<typename T>struct F {   static T const value;};template<> struct F<int> { // Specialization    static int const value; }; template struct F<int>;template<typename T>T const F<T>::value = sizeof(T);template<>int const F<int>::value = 42;int main() {    struct F<int> ma;    cout << ma.value;    return 0;}

http://ideone.com/wvrurz

而在MSVC 2012上,我无法得到它来编译：

#include <iostream>using namespace std;template<typename T>struct F {  static T const value;};template<> struct F<int> { // Specialization    static int const value; };//template struct F<int>; // error C2950: 'F<int>' : cannot explicitly instantiate an explicit specializationtemplate<typename T>T const F<T>::value = sizeof(T);//template<>//int const F<int>::value = 42; // error C2998: 'const int F<int>::value' : cannot be a template deFinitionint main() {    struct F<int> ma;    cout << ma.value;    return 0;}

从我在n3242§14.7中读到的5

both an explicit instantiation and a declaration of an explicit
specialization shall not appear in a program unless the explicit
instantiation follows a declaration of the explicit specialization.

我相信是这样的.我错过了什么吗？

解决方法 太长;不阅读

> msvc 2012正确拒绝标记为//错误C2998的行,
>以前的诊断是错误的,应该被接受;因为它是在newer versions的编译器.

注意：有关C2950的错误报告可以在here找到.

关于C2950

msvc 2012是错误的发出相关行的诊断.

template<class T> struct A;template<>struct A<int> { };template struct A<int>; // legalint main () { }

该标准规定明确的实例化应该包含一个简单的模板ID,这正是A< int>是这样说的这是合法的C.

14.6.2p3 Explicit instantiation [temp.explicit]

If the explicit instantiation is for a class or member class,the elaborated-type-specifIEr in the declaration shall include a simple-template-ID.

14.2p1 names of template specializations [temp.names]

A template specialization (14.7) can be referred to by a template-ID:

06001

措辞变更：C 03与C 11

14.7.2p5从C11开始有一些新的措辞,在以下缺陷报告之后就已经到位了：

> 259. Restrictions on explicit specialization and instantiation

14.7.2p5 Explicit instantiation [temp.explicit]

For a given set of template arguments,if an explicit instantiation of a template appears after a declaration of an explicit specialization for that template,the explicit instantiation has no effect.

^{Note: Kudos to @07004 for bringing attention to the prevIoUsly linked DR.}

关于C2998

这个错误是准确的你不是指依赖于模板参数的东西,这意味着你不应该使用模板<>关于有关定义.

较新版本的gcc会对其进行诊断,并且cl声正确地拒绝这样的定义.

template<class T> struct A;template<>struct A<int> {   static int const value;};template<> int const A<int>::value = 42; // ill-formed,`value` does not depend on                                         //              any template parameter since it's                                         //              explicitly a part of `A<int>`int main () { }

gcc   => foo.cpp:8:22: warning: too many template headers for A<int>::value (should be 0)clang => foo.cpp:8:1: error: extraneous 'template<>' in declaration of variable 'value'msvc  => foo.cpp(8) : error C2998: 'const int A<int>::value' : cannot be a template deFinition

以上诊断是正确的.

有关的问题是违反本标准的以下部分：

14.7.3p5 Explicit specialization [temp.expl.spec]

Members of an explicitly specialized class template are defined in the same manner as members of normal class,and not using the template<>Syntax. The same is true when defining a member of an explicitly specialized member class.

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