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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Dear MPI Group,<br>
<br>
I'm wondering if the files created with the modes <br>
<br>
MPI_MODE_CREATE | MPI_MODE_WRONLY <br>
<br>
will be truncated to 0 if the file already exists calling MPI_File_open(...). <br>
<br>
As far as I tested it and also which is written in the standard:<br>
<br>
MPI_MODE_CREATE — create the file if it does not exist<br>
MPI_MODE_WRONLY — write only<br>
<br>
The existing file will be overwritten, but leaving the bytes that have not been explicitly overwritten. Thus, an existing file with the size of 8 Bytes and data to be written to of 4 Bytes will still be 8 Bytes after writing: With the 4 Bytes of the new data
and 4 Bytes of the old data.<br>
<br>
As I read it, there is nothing defined what happens with the data of the file if it already exists [p 494, 1].<br>
<br>
The POSIX / GNU lib c standard states that the file will be truncated to 0 if opened with 'w' and the file does already exists calling fopen(...) [p. 249, 2]:<br>
<br>
‘w’ - Open the file for writing only. If the file already exists, it is truncated to zero length. Otherwise a new file is created.<br>
<br>
I really would appreciate some input if I'm wrong or not and what to do if the file needs to be truncated before writing (other then deleting the file before).<br>
<br>
Kind regards<br>
<br>
Florian Willich<br>
<br>
[1]: Message Passing Interface Forum. 2015. MPI: A Message-Passing Interface Standard Version 3.1. http://mpi-forum.org/docs/mpi-3.1/mpi31-report.pdf. [Online. Accessed 2nd December 2015].<br>
<br>
[2]: Loosemore, Sandra, Stallman, Richard M., McGrath, Roland, Oram, Andrew, & Drepper, Ulrich. 2015. The GNU C Library Reference Manual. http://www.gnu.org/software/libc/manual/pdf/libc.pdf. [Online. Accessed 24th January 2016].<br>
<br>
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</b></font><font color="#666666"><b>und Raumfah</b></font><font color="dimgray"><b>rt</b></font><font color="dimgray"> e. V. (DLR)</font></font></span></font></div>
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<div style="margin:0px"><font face="Calibri,sans-serif" size="2"><span style="font-size:11pt"><font color="dimgray">Florian Willich| Candidate for Bachelor of Science<br>
Software Developer (Parallel Applications)</font></span></font></div>
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