使用向量<char>作为缓冲区而不在 resize() 上初始化它

问题描述

我想使用 vector 作为缓冲区.该界面非常适合我的需求，但在将其调整为超出当前大小时会降低性能，因为内存已初始化.我不需要初始化，因为在任何情况下数据都会被某些第三方 C 函数覆盖.有没有办法或特定的分配器来避免初始化步骤?请注意，我确实想使用 resize()，而不是像 reserve() 和 capacity() 之类的其他技巧，因为我需要 size() 始终表示我的缓冲区"的有效大小，而 capacity() 在 resize() 之后可能大于其大小>，所以，我不能依赖 capacity() 作为我的应用程序的重要信息.此外，向量的(新)大小永远不会提前知道，所以我不能使用 std::array.如果无法以这种方式配置矢量，我想知道我可以使用哪种容器或分配器来代替 vector.唯一的要求是，vector 的替代方案最多必须基于 STL 或 Boost.我可以访问 C++11.

I want to use vector<char> as a buffer. The interface is perfect for my needs, but there's a performance penalty when resizing it beyond its current size, since the memory is initialized. I don't need the initialization, since the data will be overwritten in any case by some third-party C functions. Is there a way or a specific allocator to avoid the initialization step? Note that I do want to use resize(), not other tricks like reserve() and capacity(), because I need size() to always represent the significative size of my "buffer" at any moment, while capacity() might be greater than its size after a resize(), so, again, I cannot rely on capacity() as a significative information for my application. Furthemore, the (new) size of the vector is never known in advance, so I cannot use std::array. If vector cannot be configured that way, I'd like to know what kind of container or allocator I could use instead of vector<char, std::alloc>. The only requirement is that the alternative to vector must at most be based on STL or Boost. I have access to C++11.

推荐答案

标准库中没有任何内容可以满足您的要求，我也不知道 boost 中的任何内容.

There's nothing in the standard library that meets your requirements, and nothing I know of in boost either.

我能想到三个合理的选择:

There are three reasonable options I can think of:

• 暂时坚持使用 std::vector，在代码中留下注释，如果这会导致您的应用程序出现瓶颈，请返回.
• 使用带有空 construct/destroy 方法的自定义分配器 - 并希望您的优化器足够聪明以删除对它们的任何调用.
• 围绕动态分配的数组创建一个包装器，仅实现您需要的最少功能.

• Stick with std::vector for now, leave a comment in the code and come back to it if this ever causes a bottleneck in your application.
• Use a custom allocator with empty construct/destroy methods - and hope your optimiser will be smart enough to remove any calls to them.
• Create a wrapper around a a dynamically allocated array, implementing only the minimal functionality that you require.

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