确定流结束时出现EOF问题

问题描述

当我尝试使用函数 feof(FILE *) 确定文件结尾时，我发现它没有按预期工作:即使流结束，也需要额外读取.例如feof(FILE*) 如果在读取 10 个字节后立即调用具有 10 个字节数据的文件，则不会告诉 true.我需要一个额外的读取操作，当然返回 0，然后 feof(FILE *) 会说好的，现在你到了."

When I try to determine end of file with function feof(FILE *), I find it does not work as I expected: an extra read is required even if the stream does end. e.g. feof(FILE*) will not tell true if invoked on a file with 10 bytes data just after reading 10 bytes out. I need an extra read operation which of course return 0, then feof(FILE *) will say "OK, now you reach the end."

我的问题是为什么还需要一个 read 以及如何确定文件的结尾，或者如果我不想要 feof-style?

My question is why does one more read required and how to determine end of file or how to know how many bytes left in a file stream if I don't want the feof-style?

谢谢和最好的问候.

推荐答案

不要使用 feof() 或任何变体 - 就这么简单.您希望它以某种方式预测下一次读取将失败，但这不是它的作用 - 它告诉您上一次读取的结果是什么.读取文件的正确方法是(在伪代码中):

Do not use feof() or any variants - it is as simple as that. You want it to somehow predict the next read will fail, but that's not what it does - it tells you what the result of the PREVIOUS read was. The correct way to read a file is (in pseudocode):

while( read( file, buffer ) ) {
   do something with buffer
}

也就是说，需要测试读操作的结果.对于 C 流和 C++ iostream 都是如此.

In other words, you need to test the result of the read operation. This is true for both C streams and C++ iostreams.

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