如何重用 ostringstream?

问题描述

我想清除并重用一个 ostringstream(和底层缓冲区)，这样我的应用程序就不必进行那么多的分配.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

我以前用过 clear 和 str 的序列:

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完成了.或者，您可以手动清除，然后寻找合适的顺序开始:

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

这将通过覆盖当前输出缓冲区中的任何内容来防止 str 进行一些重新分配.结果是这样的:

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");

如果你想在 c 函数中使用字符串，你可以使用 std::ends，像这样放置一个终止空值:

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 是弃用的 std::strstream 的产物，它能够直接写入您在堆栈上分配的字符数组.您必须手动插入终止空值.但是，std::ends 并没有被弃用，我认为因为它在上述情况下仍然很有用.

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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