如何重用一个ostringstream？ [英] How to reuse an ostringstream?

问题描述

我想清除和重用一个ostringstream（和底层缓冲区），这样我的应用程序不必做很多分配。如何将对象重置为其初始状态？

I'd like to clear out and reuse an ostringstream (and the underlying buffer) so that my app doesn't have to do as many allocations. How do I reset the object to its initial state?

推荐答案

我在过去使用了一系列clear和str：

I've used a sequence of clear and str in the past:

// clear, because eof or other bits may be still set. 
s.clear();
s.str("");

这对输入和输出字符串流都做了。或者，您可以手动清除，然后寻找适当的顺序到开始：

Which has done the thing for both input and output stringstreams. Alternatively, you can manually clear, then seek the appropriate sequence to the begin:

s.clear();
s.seekp(0); // for outputs: seek put ptr to start
s.seekg(0); // for inputs: seek get ptr to start

这将阻止 str 通过覆盖输出缓冲区中的任何内容。结果如下：

That will prevent some reallocations done by str by overwriting whatever is in the output buffer currently instead. Results are like this:

std::ostringstream s;
s << "hello";
s.seekp(0);
s << "b";
assert(s.str() == "bello");

如果要使用c函数的字符串，可以使用 std :: ends ，设置一个终止空如下：

If you want to use the string for c-functions, you can use std::ends, putting a terminating null like this:

std::ostringstream s;
s << "hello";
s.seekp(0);
s << "b" << std::ends;
assert(s.str().size() == 5 && std::strlen(s.str().data()) == 1);

std :: ends 已弃用的 std :: strstream ，它能够直接写入您在堆栈上分配的char数组。您必须手动插入终止空。但是， std :: ends 不是不推荐使用，我认为，因为它仍然有用，因为在上述情况。

std::ends is a relict of the deprecated std::strstream, which was able to write directly to a char array you allocated on the stack. You had to insert a terminating null manually. However, std::ends is not deprecated, i think because it's still useful as in the above cases.

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