fseek(...,SEEK_CUR) calls _fflush_r(ptr, fp) in read only mode

fseek(...,SEEK_CUR) calls _fflush_r(ptr, fp) in read only mode

[Xiaofeng Liu via cygwin]

In ftello.c, it intentionally skipped fflush for read mode:
https://github.com/openunix/cygwin/blob/master/newlib/libc/stdio/ftello.c#L121

/* Find offset of underlying I/O object, then adjust for buffered     bytes.  Flush a write stream, since the offset may be altered if     the stream is appending.  Do not flush a read stream, since we     must not lose the ungetc buffer.  */  if (fp->_flags & __SWR)    _fflush_r (ptr, fp);
But in fseeko.c, when fseek(..., SEEK_CUR) requires to get the current position first. But it calls _fflush_r(ptr, fp) in read mode, which screwed up the current position after fflush. 
https://github.com/openunix/cygwin/blob/master/newlib/libc/stdio/fseeko.c#L174


For my job, if I skip _fflush_r for read only mode in fseek(..., SEEK_CUR), the job runs OK. 
Considering fseek(..., SEEK_CUR) is a basic call, could my understanding be wrong? 
Thanks.
Xiaofeng Liu
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Re: fseek(...,SEEK_CUR) calls _fflush_r(ptr, fp) in read only mode

[Corinna Vinschen]

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On Dec  1 17:02, Xiaofeng Liu via cygwin wrote:
> In ftello.c, it intentionally skipped fflush for read mode:
> https://github.com/openunix/cygwin/blob/master/newlib/libc/stdio/ftello.c#L121
> 
> /* Find offset of underlying I/O object, then adjust for buffered     bytes.  Flush a write stream, since the offset may be altered if     the stream is appending.  Do not flush a read stream, since we     must not lose the ungetc buffer.  */  if (fp->_flags & __SWR)    _fflush_r (ptr, fp);
> But in fseeko.c, when fseek(..., SEEK_CUR) requires to get the current position first. But it calls _fflush_r(ptr, fp) in read mode, which screwed up the current position after fflush. 
> https://github.com/openunix/cygwin/blob/master/newlib/libc/stdio/fseeko.c#L174
> 
> 
> For my job, if I skip _fflush_r for read only mode in fseek(..., SEEK_CUR), the job runs OK. 
> Considering fseek(..., SEEK_CUR) is a basic call, could my understanding be wrong? 

Please provide a simple, self-contained testcase.  It might clear
up the problem.


Corinna

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Corinna Vinschen                  Please, send mails regarding Cygwin to
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