dup2之后，流仍然包含旧内容？
所以如果我这样做：
dup2(0, backup); // backup stdin
dup2(somefile, 0); // somefile has four lines of content
fgets(...stdin); // consume one line
fgets(....stdin); // consume two lines
dup2(backup, 0); // switch stdin back to keyboard
我现在发现.. stdin 仍然包含我没有消耗的两行。这是为什么？因为无论重定向多少次，都只有一个缓冲区？当我想返回时，如何摆脱剩下的两行，但仍然记得我在 somefile 流中的位置？
so if I do:
dup2(0, backup); // backup stdin
dup2(somefile, 0); // somefile has four lines of content
fgets(...stdin); // consume one line
fgets(....stdin); // consume two lines
dup2(backup, 0); // switch stdin back to keyboard
I am finding at this point.. stdin still contains the two lines I haven't consumed. Why is that? Because there is just one buffer no matter how many times you redirect? How do I get rid of the two lines left but still remember where I was in the somefile stream when I want to go back to it?
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您还没有刷新标准输入缓冲区。即使底层文件描述符已恢复，它也缓冲了某个文件的所有行。
You haven't flushed the stdin buffer. It has buffered up all the lines of somefile even if the underlying file descriptor is restored.