Oompi String Example

The Object Oriented Message Passing Interface (OOMPI) does not have a means of directly transmitting strings between processes. This problem can be solved by building a class which can encapsulate the two steps needed for transmitting a string. Those steps are

• Send the size of the string.
• Send an array of chars which contains the content of the string.

The wrapping class then handles at each end the conversion from and to a string object which is inside the class. It is easy to extend this so that the user can directly send and receive string objects. -- JohnFletcher

See also ObjectOrientedMessagePassingInterface MessagePassingInterface ParallelProgrammingModel

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Example program which shows use of the class OOMPI_string

 #include <iostream>
 #include <sstream>
 #include <string>
 #include <vector>
 #include "oompi.h"
 using namespace std;
 // ===============================================================================
 // OOMPI_string definition
 // ===============================================================================
 class OOMPI_string {
 public:
  OOMPI_string() : num(0) { }
  OOMPI_string(const string &ss) : s(ss) { num = s.length() + 1; }
  void Send(OOMPI_Port &to);
  void Recv(OOMPI_Port &from);
  // Set send true for the process which is sending.
  void Bcast(OOMPI_Port &from,bool send=false);
  void Gather(OOMPI_Port &to);
  vector<string> Gather(OOMPI_Port &to,int size,
            int *string_sizes,int *string_displ);
  void Scatter(OOMPI_Port &from);
  void Scatter(OOMPI_Port &from,const vector<string> &v,
            int size,int *string_sizes,int *string_displ);
  void Set(const string &ss) { s = ss; num = s.length() + 1; }
  string Get() const { return s; }
  int Size() const { return num; }
  friend OOMPI_Port& operator << (OOMPI_Port& p,const OOMPI_string &s);
  friend OOMPI_Port& operator >> (OOMPI_Port& p,const OOMPI_string &s);
 private:
  string s;
  int num;
 };
 // ===============================================================================
 // OOMPI_string implementation 
 // ===============================================================================
 // Implementation not included for reasons of space,
 // except for these overloads which hide the OOMPI_string in the user code  
 // and allow strings to be used directly.
 OOMPI_Port& operator << (OOMPI_Port& p,const string &s)
 {
  OOMPI_string os(s);
  os.Send(p);
  return p;
 }

 OOMPI_Port& operator >> (OOMPI_Port& p,string &s)
 {
  OOMPI_string os;
  os.Recv(p);
  s = os.Get();
  return p;
 }

 int main(int argc, char *argv[])
 {
  OOMPI_COMM_WORLD.Init(argc, argv);
  int rank = OOMPI_COMM_WORLD.Rank();
  int size = OOMPI_COMM_WORLD.Size();
  OOMPI_Port to   = OOMPI_COMM_WORLD[0];
  string hello("Hello");
  if (rank == 0) {
      int where;
      for (where = 1; where < size; where++) {
         string how;
         OOMPI_Port source = OOMPI_COMM_WORLD[where];
         source >> how;
         cout << rank << " has " << how << " from " << where << endl;
      }
  } else {
      ostringstream out;
      out << rank << " says " << hello << endl; 
      to << out.str();
  }  
  OOMPI_COMM_WORLD.Finalize();
  return 0;
 }

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CategoryCpp