I still feel the standard obscures the case. Passing a buffer (value) and the length of the buffer (valuelen) is easier for programmers. The Fortran interface "CHARACTER(LEN=valuelen), INTENT(OUT) :: value" is clearer in this regard. --Junchao Zhang On Tue, Feb 3, 2015 at 5:33 PM, Thakur, Rajeev <[email protected]> wrote:

I guess it may have been defined that way because in Fortran strings are not null-terminated. The definition in the standard allows the same value to be returned/passed in valuelen in both C and Fortran.

Rajeev

On Feb 3, 2015, at 5:28 PM, Junchao Zhang <[email protected]> wrote:

...

OK, I guess MPI standard wants to have this kind of code.

int valuelen; MPI_Info_get_valuelen(..., &valuelen,...); int buflen = valuelen + 1; char* value = (char *)malloc(buflen); MPI_Info_get(..., valuelen, value, ...);

Though, from a user's point of view, I fell better if it was MPI_Info_get(..., buflen, value, ...), that is, using buflen to specify the length of buffer I pass to MPI.

--Junchao Zhang

On Tue, Feb 3, 2015 at 4:26 PM, William Gropp <[email protected]> wrote: 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 <[email protected]> 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 _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss <test.c>

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