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C: scatterv/gatherv a 2D array

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# 1  
Old 01-19-2016
C: scatterv/gatherv a 2D array
Hello everyone,

I am new to MPI in C, and i am trying to scatter the rows in a 2D array of char, do some computations and after gather the 2D array again. Let's say that i use 4 processes:

I declare the global array and the local array here:
Code:
char global[20][3];
char local[5][3];
int my_rank;
int p;

and after i initialize mpi and scatter:
Code:
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
MPI_Comm_size(MPI_COMM_WORLD, &p);
MPI_Scatter(global, 15, MPI_CHAR, local, 15, MPI_CHAR, 0, MPI_COMM_WORLD);

And that works just fine.
But what if the user gives the size of the arrays, and i malloc the arrays ?
Code:
char **global;
global = (char **)malloc(20*sizeof(char*));
for(int i=0;i<3;i++) 
    global[i] = (char *)malloc(3*sizeof(char));
char **local;
local = (char **)malloc(5*sizeof(char*));
for(int i=0;i<3;i++)
    local[i] = (char *)malloc(3*sizeof(char));

Last edited by giampoul; 02-08-2016 at 06:36 PM..
# 2  
Old 02-08-2016
Anyone ?
# 3  
Old 02-08-2016
There is more to this than just one small example of code can fix. I found a pretty complete discussion here. READ the whole thing because there are several gotchas.
Try:


Malloc and MPI
This User Gave Thanks to jim mcnamara For This Post:
giampoul
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