同时写入两个流 [英] Write simultaneousely to two streams

问题描述

有没有办法将两个流（或文件描述符）连接在一起，以便写入一个流也将写入第二个流？ （C，Linux）

Is there a way to to couple two streams (or file descriptors) together so that writing to one stream will also write to the second one? (C, Linux)

谢谢。

推荐答案

用户laalto是正确，但在Linux上，您正在寻找的功能称为 fopencookie 。更正laalto的Linux示例导致：

User laalto is correct, but on Linux, the function you are looking for is called fopencookie. Correcting laalto's example for Linux results in:

int my_writefn(void *cookie, const char *data, int n) {
  FILE **files = (FILE **)cookie;
  fwrite(data, n, 1, files[0]);
  return fwrite(data, n, 1, files[1]);
}

int noop(void) { return 0; }
cookie_io_functions_t my_fns = {
  (void*) noop,
  (void*) my_writefn,
  (void*) noop,
  (void*) noop
};

FILE *files[2] = ...;

FILE *f = fopencookie((void *)files, "w", my_fns);

// ... use f as you like ...

当您写入 f 时，系统将执行 my_writefn 函数，并将传递给<$ c的数据传递给它$ C> fwrite的。为了简化操作，您可能还希望将文件流的缓冲更改为面向行：

When you write to f, the system will execute your my_writefn function passing it the data that was passed to fwrite. To make things easier, you may also want to change the buffering for your file stream to be line oriented:

setvbuf(f, NULL, _IOLBF, 0);

这将缓冲传递给 fwrite的数据直到输出换行符或从连接到进程的任何流中读取任何数据（例如stdin）。 注意：您必须在 fopencookie 之后但在将任何数据写入流之前调用 sevbuf 。

That will buffer up the data passed to fwrite until a newline is output or any data is read from any stream attached to the processes (e.g. stdin). NOTE: you must call sevbuf after fopencookie but before any data is written to the stream.

我使用行缓冲，因为我通常使用 fopencookie 将stderr重定向到syslog，或通过网络套接字，以及面向处理线的数据更容易，更有效。

I use line buffering because I usually use fopencookie to redirect stderr to syslog, or over a network socket, and processing line oriented data is easier and more efficient.

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