模板编译：gcc vs VS2010 [英] Templates compilation: gcc vs VS2010

问题描述

从这本书 - David，Nicolai的C ++模板：完整指南

From the book - C++ Templates: The Complete Guide by David, Nicolai

Thus, templates are compiled twice:

1. 如果没有实例化，则会检查模板代码本身是否有正确的语法。发现语法错误，例如缺少
   分号。


2. 在实例化时，将检查模板代码以确保所有调用都有效。发现无效的来电，例如
   不支援的函式呼叫。

，我写了 -

template<typename T>
void foo( T x)
{
   some illegal text
}

int main()
{
   return 0;
}

它在Visual Studio 2010上构建得很好，但是，在gcc-4.3.4上失败了。哪一个符合C ++标准？是否强制模板代码即使使用模板实例化也可以编译？

It build fine on Visual Studio 2010 with out any warnings with optimizations turned off. How ever, it failed on gcc-4.3.4. Which one is complying to the C++ standard ? Is it mandatory for template code to get compiled even with out template instantiation ?

推荐答案

有问题的程序是错误的， C ++标准在这种情况下不需要诊断，因此Visual Studio和GCC都以兼容的方式运行。从C ++ 03标准的§14.6/ 7（强调我的）：

The program in question is ill-formed, but the C++ standard does not require a diagnostic in this case, so both Visual Studio and GCC are behaving in a compliant fashion. From §14.6/7 of the C++03 standard (emphasis mine):

知道哪些名称是类型名称允许每个模板定义。对于可以生成有效专业化的模板定义，不应发布
诊断。 如果没有为模板定义生成
有效的专门化，并且该模板未实例化，则模板
定义不合格，无需诊断。如果使用类型在非依赖名称中是不完整的
，在模板被定义但在完成实例化的时间点完成，
如果该类型的完整性影响是否程序格式良好或影响程序的语义
，程序是不成形的;不需要诊断。 [注意：如果模板被实例化，
错误将根据本标准中的其他规则进行诊断。正是当这些错误被诊断时
是一个实施质量问题。 ] [示例：

Knowing which names are type names allows the syntax of every template definition to be checked. No diagnostic shall be issued for a template definition for which a valid specialization can be generated. If no valid specialization can be generated for a template definition, and that template is not instantiated, the template definition is ill-formed, no diagnostic required. If a type used in a non-dependent name is incomplete at the point at which a template is defined but is complete at the point at which an instantiation is done, and if the completeness of that type affects whether or not the program is well-formed or affects the semantics of the program, the program is ill-formed; no diagnostic is required. [Note: if a template is instantiated, errors will be diagnosed according to the other rules in this Standard. Exactly when these errors are diagnosed is a quality of implementation issue. ] [Example:

int j;
template<class T> class X {
    // ...
    void f(T t, int i, char* p)
    {
        t = i; // diagnosed if X::f is instantiated
               // and the assignment to t is an error
        p = i; // may be diagnosed even if X::f is
               // not instantiated
        p = j; // may be diagnosed even if X::f is
               // not instantiated
    }
    void g(T t) {
        +; //may be diagnosed even if X::g is
           // not instantiated
    }
};

- end example ]

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