在 C++ 中事后添加常量；

发布于 2024-09-19 10:19:13 字数 969 浏览 7 评论 0原文

可能的重复：
是否有一些忍者技巧变量声明后使其常量？

考虑以下最小示例：

void MutateData(std::string&);

int main()
{
  std::string data = "something that makes sense to humans.";

  ::MutateData(data); // Mutates 'data' -- e.g., only changes the order of the characters.

  // At this point, 'data' should never be changed.
  // Mixing the above with const-correct code seems ugly.
}

目前，我正在做：

namespace
{
  std::string PrepareData(std::string data)
  {
    ::MutateData(data);

    return data;
  }
}

int main()
{
  const std::string data = ::PrepareData("something that makes sense to humans.");
}

在声明点之外模拟 const 有哪些优雅的解决方案？

编辑：我忘记澄清我不能轻易（不是我的代码）更改MutateData。

原文

Possible Duplicate:
Is there some ninja trick to make a variable constant after its declaration?

Consider the following minimal example:

void MutateData(std::string&);

int main()
{
  std::string data = "something that makes sense to humans.";

  ::MutateData(data); // Mutates 'data' -- e.g., only changes the order of the characters.

  // At this point, 'data' should never be changed.
  // Mixing the above with const-correct code seems ugly.
}

Currently, I'm doing:

namespace
{
  std::string PrepareData(std::string data)
  {
    ::MutateData(data);

    return data;
  }
}

int main()
{
  const std::string data = ::PrepareData("something that makes sense to humans.");
}

What are some elegant solutions to simulating const beyond the point of declaration?

EDIT: I forgot to clarify that I can't easily (not my code) change MutateData.

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何时共饮酒 2024-09-26 10:19:13

您可以使用 const 引用。
看看 http ://herbsutter.com/2008 了解其工作原理的解释。

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傲世九天 2024-09-26 10:19:13

怎么样：

string MakeData(string const&)
{
    ...
    return string(...);  // for return value optimization
}

后跟与

int main()
{
    string const& str = MakeData("Something that makes sense to humans");
}

您所做的不同之处在于使用 const 引用，并且仅使用一个函数。如果您无法更改 MutateData，请按照您的建议进行操作（尽管使用 const 引用）

What about:

string MakeData(string const&)
{
    ...
    return string(...);  // for return value optimization
}

followed by

int main()
{
    string const& str = MakeData("Something that makes sense to humans");
}

The difference with what you do is using a const reference, and only one function. If you cannot change MutateData, do what you suggested (with the const reference though)

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