Array of Structures in C with MPI

Question

I am having a relatively a problem,I have defined struct and I want the array of structure has this information (processor name and the computation time for the processor) this is part of my code :

struct stru
{
   double  arr_time[50];
   char pname[50];   
};
int main (int argc, char *argv[])
{

struct stru all_info[50];

   MPI_Status status;
   MPI_Init(&argc,&argv);
   MPI_Comm_rank(MPI_COMM_WORLD,&process_id);
   MPI_Comm_size(MPI_COMM_WORLD,&num_of_processes);

    char processor_name[MPI_MAX_PROCESSOR_NAME];
    int name_len;
    MPI_Get_processor_name(processor_name, &name_len);
if (process_id == 0)
{  //do somthing
}
if (process_id > 0)
{  
    double start = MPI_Wtime();
    for (k=0; k<array_size; k++)
      for (i=0; i<rows; i++)
      {
          c[i][k]=0.0;                     
          for (j=0; j<array_size; j++)
           c[i][k] = c[i][k] + a[i][j] * b[j][k];
      }      
      end_time = MPI_Wtime() - start;  
        all_info[i].arr_time[i] = end_time;
      for (int i=1 ;i <= numworkers ;i++)
            strcpy( all_info[i].pname, processor_name);

         printf(" time  = %f  for processor %s 
         \n",all_info[i].arr_time, all_info[i].pname);

}


      MPI_Gather( &end_time, 1, MPI_DOUBLE, &all_info[i].arr_time, 1, 
       MPI_DOUBLE, 0, MPI_COMM_WORLD);

if (process_id == 0){

      for(i = 1; i <= numworkers; i++ )
      {
         printf("  time   %f  for processor %s 
         \n",all_info[i].arr_time , all_info[i].pname);
 }     }

I have no result if I print it in if (process_id == 0) !!! the out put is

 time   0.000000  for processor  
 time   0.000000  for processor  
 time   0.000000  for processor

and just the time printed if I printting in if (process_id > 0)

In fact I don't know how can I use Structure with MPI can anyone give me advice how can I generate array of structure that has processor name and his time? Thank you in advance for your time.

Please indent & format your code properly, it's hard to read now. — meaning-matters
– meaning-matters, Commented Dec 23, 2017 at 19:06
this is part of my code I'm just asking how can I putting (end_time and processor_name ) in array of structure ? — eleen
– eleen, Commented Dec 23, 2017 at 19:11
It's a matter of being nice and formatting code well prevents mistakes. — meaning-matters
– meaning-matters, Commented Dec 23, 2017 at 19:20
Meanwhile, please make the effort to post a correctly indented code that compiles. — Gilles Gouaillardet
– Gilles Gouaillardet, Commented Dec 24, 2017 at 2:20
@Gilles Gouaillardet , all the idea I want the array of structure must has the name and time for each processor that work in parallel (each processor has time and name) — eleen
– eleen, Commented Dec 24, 2017 at 11:42

halfer · Accepted Answer · 2017-12-29 21:04:57Z

3

At this line:

processor_name[MPI_MAX_PROCESSOR_NAME];

you start using the array variable processor_name without defining it anywhere.

You're missing something like all_info[i]. in front of it. Like you have a bit lower:

all_info[i].processor_name;

Then, for storing a string your processor_name needs memory. A single char is just one byte (i.e. one letter). So let's assume these names are never longer than 255, you'd get:

struct stru
{
   double end_time;
   char   processor_name[256];   
};

There are so many basic things wrong in your code and your questions seem to indicate that you lack basic understanding of C programming. Therefore my advice would be to take more time studying this language.

edited Dec 29, 2017 at 21:04

halfer

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answered Dec 23, 2017 at 19:04

meaning-matters

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4 Comments

eleen Over a year ago

I defined it in structure, but I don't know if this true or no ?

eleen Over a year ago

I do your update and this error I have ( error: ‘processor_name’ undeclared (first use in this function) processor_name[MPI_MAX_PROCESSOR_NAME]; )

eleen Over a year ago

I update my code and I got rid of the mistake , but I have no result when printing the result ... thank you and Merry Christmas! :)

eleen Over a year ago

for this hint "char processor_name[256]; " plus one

Dakshraj Sharma · Accepted Answer · 2017-12-23 19:16:03Z

1

The error occurs here because you have not defined any type processor name. If I understand what you're trying to correctly, it seems like you were trying to access the attribute of the structures. For doing that, you might need to use the . operator. For that you might need to define an array

struct stru all_info[MPI_MAX_PROCESSOR_NAME];

instead of

struct stru all_info[50];

answered Dec 23, 2017 at 19:16

Dakshraj Sharma

1511 silver badge5 bronze badges

3 Comments

eleen Over a year ago

in this case I reache just for the processor name ?? is that correct ??

eleen Over a year ago

I want all info array must contain the processor name and the time that I compute

eleen Over a year ago

I update my code and I got rid of the mistake , but I have no result when printing the result .

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