MPI_CHARACTER

做了一个关于FORTRAN中MPI_CHARACTER的有趣测试：
(环境：CVF+F90+MPICH2)

program main
!USE MPI
include 'mpif.h'
character*50 message
integer myid,numprocs,ierr
integer status(MPI_STATUS_SIZE)

message="hello process 1"
call MPI_INIT(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD,myid,ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD,numprocs,ierr)

if (myid==0) then
   call MPI_SEND(message,1,MPI_CHARACTER,1,99,MPI_COMM_WORLD,ierr)
else if(myid==1) then
  call MPI_RECV(message,1,MPI_CHARACTER,0,99,MPI_COMM_WORLD,ierr,status)
   WRITE(*,*) message
end if

call MPI_FINALIZE(ierr)

end

结果显示：

如果增大message的长度，改为：hello process 1!hello process 1!hello process 1!hello process 1!

program main
!USE MPI
include 'mpif.h'
character*50 message
integer myid,numprocs,ierr
integer status(MPI_STATUS_SIZE)

message="hello process 1!hello process 1!hello process 1!hello process 1!"
call MPI_INIT(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD,myid,ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD,numprocs,ierr)

if (myid==0) then
   call MPI_SEND(message,1,MPI_CHARACTER,1,99,MPI_COMM_WORLD,ierr)
else if(myid==1) then
  call MPI_RECV(message,1,MPI_CHARACTER,0,99,MPI_COMM_WORLD,ierr,status)
   WRITE(*,*) message
end if

call MPI_FINALIZE(ierr)

end

运行结果则为：


由上对比可知：
1、MPI确实是以数据的个数来计数的，而不是以数据字节大小来计数的
   call MPI_SEND(message,1,MPI_CHARACTER,1,99,MPI_COMM_WORLD,ierr)
   call MPI_RECV(message,1,MPI_CHARACTER,0,99,MPI_COMM_WORLD,ierr,status)

2、MPI_CHARACTER最大支持50个字节的字符串
有兴趣可以做做其他类型数据的测试。