my_check_err_hello.c

#include <stdio.h>
#include <stdlib.h>
// 检查是否定义
#ifdef _OPENMP
#  include <omp.h>   
#endif 

void Usage(char* prog_name);
void Hello(int thread_count);  /* Thread function */

int main(int argc, char* argv[]) {
   int thread_count;

   if (argc != 2) Usage(argv[0]);
   thread_count = strtol(argv[1], NULL, 10); 
   if (thread_count <= 0) Usage(argv[0]);

#  pragma omp parallel num_threads(thread_count) 
   Hello(thread_count);

   return 0; 
}  /* main */

void Usage(char *prog_name) {
   fprintf(stderr, "usage: %s <thread_count>\n", prog_name);
   fprintf(stderr, "   thread_count should be positive\n");
   exit(0);
}  /* Usage */

void Hello(int thread_count) {
#  ifdef _OPENMP
      int my_rank = omp_get_thread_num();
      int actual_thread_count = omp_get_num_threads();
#  else
      int my_rank = 0;
      int actual_thread_count = 1;
#  endif

   if (my_rank == 0 && thread_count != actual_thread_count)
      fprintf(stderr, "Number of threads started != %d\n", thread_count);
   printf("Hello from thread %d of %d\n", my_rank, actual_thread_count);

}  /* Hello */