无限缓冲的printf - 格式化看跌直接流 [英] unlimited buffer printf - formatted puts directly to stream

问题描述

我的理解是，printf的大多数实现依赖于像

my understanding is that most implementations of printf rely on something like

vsnprintf( _acBuffer[0], sizeof( _acBuffer[0] ), pcFormat, *ptArgList );

要真正处理的格式，然后他们输出他们通过放流。

to actually handle the formatting and then they output them to the stream via puts.

是否有减少_acBuffer的大小任何实现[0]，同时保持打印所有字符串的能力要求？

Are there any implementation that minimize the size of _acBuffer[0] required while maintaining the ability to print all string?

显然是这样的：

printf("%s", pcReallyLongString);

将是一个问题。

您的想法是多AP preciated！

Your thoughts are much appreciated!

推荐答案

你的理解是错误的。我从来没有见过或printf 实现，首先格式化整个输出到一个临时字符串缓冲区工作听过的。通常printf的是周围的其他方法进行：基本构建块是 vfprintf 和 vsnprintf 是一个包装创造假文件的缓冲区是目标字符串。

Your understanding is just wrong. I've never seen or heard of a printf implementation that works by first formatting the entire output to a temporary string buffer. Usually printf is done the other way around: the fundamental building block is vfprintf and vsnprintf is a wrapper for that which creates a fake FILE whose buffer is the destination string.

编辑：一些流行的（如的glibc）实现做在某种程度上利用无粘结大型中间缓冲区为某些格式，尤其是宽字符转换，并且将失败未predictably当他们无法为缓冲区分配足够的内存。这纯粹是一个低质量的实现问题，但是，有没有根本的原因任何的的printf 函数应该要求比工作空间，无论他们是什么样打印的小恒量了。

Some popular (e.g. glibc) implementations do make some use of unboundedly-large intermediate buffers for certain formats, especially wide character conversions, and will fail unpredictably when they cannot allocate sufficient memory for the buffer. This is purely a low-quality-implementation issue, however; there's no fundamental reason any of the printf functions should require any more than a small constant amount of working space, regardless of what they're printing.

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