[mpich-discuss] question in MPI_Info_get

[William Gropp]

Thanks.  Yes, I believe this is a bug.  The implementation of MPI_Info_get in MPICH passes valuelen to the internal copy routine, yet it is clear that the definition in the standard for MPI_Info_get, it should pass valuelen+1 (it should also check for the error return code from the internal routine and return a value MPI error code if the buffer is too small.

Bill

On Feb 1, 2015, at 12:13 AM, Hajime Fujita <hfujita at uchicago.edu> wrote:

> Hello,
> 
> I came across some question about a behavior of MPI_Info_get in MPICH.
> 
> If I knew the size of the value, what should I pass to MPI_Info_get as `valuelen`?
> Suppose I have 3-byte value in the info object, and I allocate 4-byte buffer including a space for null-termination. Then I think I should specify 3 as valuelen to retrieve the whole value, as the MPI-3 specifications says
> "In C, valuelen should be one less than the amount of allocated space to allow for the null terminator.”
> 
> However, when I run the attached program in MPICH 3.1.1, I get:
> $ ./test
> key found: vaule=va  # The last character ‘l’ is missing
> 
> If I specify `sizeof(buff)` as valuelen, it shows “val” correctly.
> 
> So apparently MPICH thinks valuelen includes null terminator.
> Am I missing anything, or any misunderstanding here?
> 
> 
> Thank you in advance,
> Hajime
> 
> --
> Hajime Fujita
> Postdoctoral Scholar, Large-Scale Systems Group
> Department of Computer Science, The University of Chicago
> http://www.cs.uchicago.edu/people/hfujita
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