由模板成员函数引起的错误 C2275。这段代码有错吗？

发布于 2024-09-24 12:57:58 字数 1018 浏览 0 评论 0原文

我想我遇到了（可能）VC6（我知道。这就是我们使用的。）编译器错误，但我愿意接受这样一个事实：我刚刚错过了一些愚蠢的事情。给出以下代码（这只是一个示例！）：

#include <iostream>

// Class with template member function:
class SomeClass
{
public:
  SomeClass() {};

  template<class T>
  T getItem()
  {
    return T();
  };
};


// Dummy just used to recreate compiler error
class OtherClass
{
public:
  OtherClass() {};
};

std::ostream& operator<<( std::ostream& oStr, const OtherClass& obj )
{
  return oStr << "OtherClass!";
};

// Main illustrates the error:
int main(int argc, char* argv[])
{
  SomeClass a;

  OtherClass inst2 = a.getItem<OtherClass>(); // Error C2275 happens here!
  std::cout << inst2 << std::endl;

  return 0;
}

如果我尝试在 VC6 中编译此代码，则会在 a.getItem() 上崩溃，生成：

错误 C2275：“OtherClass”：非法使用此类型作为表达式。

我是否忽略了一些微不足道的语法问题？我违反规则了吗？这段代码在 gcc 4.3.4 下编译得很好。这是 VC6 的另一个合规性问题吗？

谢谢！

原文

I think I've run into a (possible) VC6 (I know. It's what we use.) compiler error, but am open to the fact that I've just missed something dumb. Given the following code (It's just an example!):

#include <iostream>

// Class with template member function:
class SomeClass
{
public:
  SomeClass() {};

  template<class T>
  T getItem()
  {
    return T();
  };
};


// Dummy just used to recreate compiler error
class OtherClass
{
public:
  OtherClass() {};
};

std::ostream& operator<<( std::ostream& oStr, const OtherClass& obj )
{
  return oStr << "OtherClass!";
};

// Main illustrates the error:
int main(int argc, char* argv[])
{
  SomeClass a;

  OtherClass inst2 = a.getItem<OtherClass>(); // Error C2275 happens here!
  std::cout << inst2 << std::endl;

  return 0;
}

If I try to compile this code VC6, dies on a.getItem<OtherClass>() yielding:

Error C2275: 'OtherClass' : illegal use of this type as an expression.

Have I overlooked some trivial syntax issue? Am I breaking a rule?
This code compiles just fine under gcc 4.3.4. Is it yet another compliance issue with VC6?

Thanks!

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剩余の解释 2024-10-01 12:57:58

除了其中包含“模板”一词的许多其他内容之外，VC6 无法处理模板参数不是函数参数的函数模板。常见的解决方法是添加一个虚拟函数参数：

  template<class T>
  T getItem(T* /*dummy*/ = NULL)
  {
    return T();
  } // note: no ; after function definitions

但是，一般来说，VC6 相当蹩脚，并且一旦 TU 包含 template 关键字，通常就会出现问题。我不得不与它搏斗了好几年（用多个编译器/编译器版本编译的大型代码库；VC6给我们带来了无穷无尽的麻烦），当我在2003年摆脱它时，我感到非常高兴。

Among many other things with the word template in it, VC6 couldn't deal with function templates where the template parameters aren't also function parameters. The common workaround was to add a dummy function parameter:

  template<class T>
  T getItem(T* /*dummy*/ = NULL)
  {
    return T();
  } // note: no ; after function definitions

However, in general, VC6 is pretty lame and often chokes as soon as a TU contains the template keyword. I had to beat my head against it for several years (big code base compiled with several compilers/compiler versions; VC6 giving us an endless amount of trouble) and was very glad when I got rid of it in 2003.

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