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哦,才看见,你的正确的代码后面是有fseek
看一个FILE只有一个指针(当前位置)的fseek实现,不难想象有两个指针的fseek
int
fseek(FILE *stream, long int offset, int whence)
{
int adjust = 0;
long pos;
stream->_flags &= ~(_IOEOF | _IOERR);
/* Clear both the end of file and error flags */
if (io_testflag(stream, _IOREADING)) {
if (whence == SEEK_CUR
&& stream->_buf
&& !io_testflag(stream,_IONBF))
adjust = stream->_count;
stream->_count = 0;
} else if (io_testflag(stream,_IOWRITING)) {
fflush(stream);
} else /* neither reading nor writing. The buffer must be empty */
/* EMPTY */ ;
pos = _lseek(fileno(stream), offset - adjust, whence);
if (io_testflag(stream, _IOREAD) && io_testflag(stream, _IOWRITE))
stream->_flags &= ~(_IOREADING | _IOWRITING);
stream->_ptr = stream->_buf;
return ((pos == -1) ? -1 : 0);
} |
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