Table of Contents

OpenMP Hello World Software Manual

Author: Philip Nelson

Language: C++. The code can be compiled using the GNU C++ compiler (gcc). A make file is included to compile an example program

For example,

make

will produce an executable ./hello.out that can be executed.

Description/Purpose: This code shows that you have OpenMP installed and are able to compile/run programs using OpenMP.

Input: There are no inputs needed in this case.

Output: This code will print out the number of availiable threads of execution availiale on the system and each thread will print “Hello World from thread #” where # is the thread’s id.

Usage/Example:

The code can be run on a Linux commandline as shown below:

# ./hello.out

Output from the lines above

Number of threads is 4
Hello World from thread 0
Hello World from thread 3
Hello World from thread 1
Hello World from thread 2

The first line displays the number of threads of execution available on the system. The following lines are messages from each thread ending in their thread id.

Implementation/Code: The following is the code for helloWorld.cpp

#include <iostream>
#include <omp.h>

int main()
{
  int tid = 0;

// Fork a team of threads giving them their own copies of variables
#pragma omp parallel private(tid)
  {
    // Obtain thread id number
    tid = omp_get_thread_num();

    // Only master thread does this
    if (tid == 0)
    {
      int thread_ct = omp_get_num_threads();
      std::cout << "Number of threads is " << thread_ct << '\n';
    }

    std::cout << "Hello World from thread " << tid << '\n';

  } // All threads join master thread and disband

  return EXIT_SUCCESS;
}

Last Modified: September 2018