我应该预分配std :: stringstream？ [英] Should I preallocate std::stringstream?

问题描述

我使用 std :: stringstream 广泛地在我的应用程序中构造字符串和错误消息。 stringstreams 通常是非常短的生命自动变量。

这样的使用会导致每个变量的堆重新分配吗？我应该从临时切换到类成员 stringstream 变量吗？

在后一种情况下， c $ c> stringstream 缓冲区？ （我应该用足够大的字符串初始化它还是有更优雅的方法？）

解决方案

并发现它们是减速的来源？

考虑它们的用法。

至于预留空间...

一些实现可能在对stringstream进行任何分配之前保留一个小缓冲区。 std :: string的许多实现都会执行此操作。

另一个选项可能是（未测试！）

  std :: string str; 
 str.reserve（50）; 
 std :: stringstream sstr（str）; 
  

您可能会在 gamedev线程。

edit： p>

使用 stringstream的rdbuf 进行处理也可能是一个解决方案。这种方法可能很容易弄错，请确保绝对必要 。绝对不优雅或简洁。

I use std::stringstream extensively to construct strings and error messages in my application. The stringstreams are usually very short life automatic variables.

Will such usage cause heap reallocation for every variable? Should I switch from temporary to class-member stringstream variable?

In latter case, how can I reserve stringstream buffer? (Should I initialize it with a large enough string or is there a more elegant method?)

解决方案

Have you profiled your execution, and found them to be a source of slow down?

Consider their usage. Are they mostly for error messages outside the normal flow of your code?

As far as reserving space...

Some implementations probably reserve a small buffer before any allocation takes place for the stringstream. Many implementations of std::string do this.

Another option might be (untested!)

std::string str;
str.reserve(50);
std::stringstream sstr(str);

You might find some more ideas in this gamedev thread.

edit:

Mucking around with the stringstream's rdbuf might also be a solution. This approach is probably Very Easy To Get Wrong though, so please be sure it's absolutely necessary. Definitely not elegant or concise.

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