fprintf 到文件和标准输出 [英] fprintf both to file and to stdout

问题描述

我的 C 程序预计会产生大量输出.

My C program is expected to produce a lot of output.

其中一些输出行是特殊的，我想将副本写入特殊文件.我结束了

Some of these output lines are special and I would like to write a copy to a special file. I end up doing

FILE * outf = fopen("special_file", "a");
fprintf(stdout, "normal line 1\n");
fprintf(stdout, "special line!\n");
fprintf(outf,   "special line!\n");/*inelegant & dangerous code duplication*/
fprintf(stdout, "normal line 2\n");

有没有一种简单的方法可以避免这种不雅的&危险的代码重复?我有很多这样的东西，我最终可能会写出像 printf("next is %d\n", num++); 这样的东西，这些东西不能天真地复制，例如使用宏.

Is there an easy way to avoid such inelegant & dangerous code duplication? I have quite a lot of it and I may eventually write things like printf("next is %d\n", num++); that cannot be duplicated naively, e.g. using macros.

目前我认为除了生成一个将运行 tee 等效项的子进程之外，没有其他解决方案.还有其他想法吗?例如.可以定义一种 FILE* 以某种方式重定向到 stdout &outf?

At the moment I see no solution short of spawning a child process that will run a tee equivalent. Any other idea? E.g. can one define a kind of FILE* that will in some way redirect to both stdout & outf?

推荐答案

我认为 dup(2) 系统调用是您所需要的，请参阅man 2 dup".

I think the dup(2) system call is what you need, see "man 2 dup".

感谢投票，但我想我错了.

edit: thanks for the votes, but I think I got it wrong.

dup 的作用是让两个文件描述符引用一个文件.您想要的是一个引用两个文件的类似文件描述符的对象.那是完全不同的事情.

What dup does is make two file descriptors reference one file. What you want is a single file descriptor-like object that references two files. That's quite a different thing.

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