printf在内部如何工作? [英] How does printf work internally?

问题描述

我很好奇printf在Linux内部如何工作.我不明白它是如何将数据写入STDOUT的.

I am curious as to how printf works internally within Linux. I don't understand how it writes data to STDOUT.

经过一番寻找内部结构的工作后，我下载了glibc并查看了源代码:

After a bit of searching for the internals, I downloaded glibc and took a look at the source code:

__printf (const char *format, ...)
{
   va_list arg;
   int done;

   va_start (arg, format);
   done = vfprintf (stdout, format, arg);
   va_end (arg);

   return done;
}

找到这个之后，我更深入地研究了vfprintf函数-但是该文件大约有2500行不熟悉的C代码.我正在寻找10,000英尺远的对printf如何与计算机内存配合并输出以在屏幕上显示字符的解释.

After finding this, I went deeper into the vfprintf function - but the file is about 2500 lines of unfamiliar C code. I'm looking for an explanation from 10,000 feet of how printf works with a computer's memory and output to display characters on screen.

如果我是一段汇编代码，我该怎么做才能完成同一任务?是否取决于操作系统?

If I were a piece of assembly code what would I have to do to accomplish the same task? Is it operating system dependent?

推荐答案

我认为您正在寻找错误的图层. vfprintf中的逻辑负责格式化其参数，并通过基础stdio函数将其写入，通常将其写入目标的FILE对象的缓冲区中.将输出输出到文件描述符的实际逻辑(或在其他非POSIX类系统上，底层的设备/文件表示形式)可能在fwrite，fputc和/或某些__前缀的内部功能(可能是__overflow).

I think you're looking at the wrong layer. The logic in vfprintf is responsible for formatting its arguments and writing them through the underlying stdio functions, usually into a buffer in the FILE object it's targetting. The actual logic for getting this output to the file descriptor (or on other non-POSIX-like systems, the underlying device/file representation) is probably in fwrite, fputc, and/or some __-prefixed internal functions (perhaps __overflow).

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