[mpich-discuss] question in MPI_Info_get

[Junchao Zhang]

Hi, Hajime,
 MPI spec also says "valuelen is the number of characters available in
value". So it seems if you should pass valuelen = 4 if value is a buffer of
4 bytes.
 I am also confused by "In C, valuelen should be one less than the amount
of allocated space to allow for the null terminator".  So I leave the
question for others.
 Interestingly, for MPI_Info_get_valuelen(), MPI spec says "The length
returned in C does not include the end-of-string".

 BTW, I found MPICH and OpenMPI have the same behavior.

--Junchao Zhang

On Sun, 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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