STL中的写时复制支持 [英] Copy-on-write support in STL

问题描述

我刚刚在阅读维基百科上写的复制文章（好奇，如果有任何并支持它的文件系统），并惊讶于以下段落：

I was just reading a Wikipedia article on Copy-on-write (curious if there are any filesystems that support it), and was surprised by the following passage:

COW也在内核，库，应用程序和系统码。例如，C ++标准库提供的字符串类是专门设计用于允许写时复制实现的：

COW is also used outside the kernel, in library, application and system code. The string class provided by the C++ standard library, for example, was specifically designed to allow copy-on-write implementations:

std::string x("Hello");

std::string y = x;  // x and y use the same buffer

y += ", World!";    // now y uses a different buffer
                    // x still uses the same old buffer

我不知道STL中每次都支持写时复制。真的吗？它适用于其他STL类，例如。 std :: vector 或 std :: array ？哪些编译器支持该优化（特别是，我不知道G ++，Intel C ++编译器和Microsoft C ++编译器）？

I didn't know that copy-on-write was every supported in STL. Is that true? Does it apply to other STL classes, e.g. std::vector or std::array? Which compilers support that optimization (in particular, I wonder about G++, Intel C++ compiler and Microsoft C++ compiler)?

推荐答案

例如，C ++标准库提供的字符串类专门设计为允许写时复制实现。

The string class provided by the C++ standard library, for example, was specifically designed to allow copy-on-write implementations

<这是半真值。是的，它开始设计与COW在心。但在急忙的std :: string的公共接口被搞砸了。导致它得到COW敌意。问题是在标准发布后发现的，我们从那以后就坚持了。作为立场目前 std :: string 不能是线程安全的COW编辑和在野外的实现不做它。

That is half-truth. Yes, it started design with COW in mind. But in the rush the public interface of std::string was messed up. Resulting it getting COW-hostile. The problems were discovered after the standard published, and we're stuck with that ever since. As stands currently std::string can not be thread-safely COW-ed and implementations in the wild don't do it.

如果您想要使用COW使用字符串，请从另一个库中获取它，例如MFC / ATL中的CString。

If you want a COW-using string, get it from another library, like CString in MFC/ATL.

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