A.22 Using the default(none) Clause

 

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The following example distinguishes the variables that are affected by the default(none) clause from those that are not:

// openmp_using_clausedefault.c  
// compile with: /openmp  
#include <stdio.h>  
#include <omp.h>  
  
int x, y, z[1000];  
#pragma omp threadprivate(x)  
  
void fun(int a) {  
   const int c = 1;  
   int i = 0;  
  
   #pragma omp parallel default(none) private(a) shared(z)  
   {  
      int j = omp_get_num_thread();  
             //O.K.  - j is declared within parallel region  
      a = z[j];       // O.K.  - a is listed in private clause  
                      //      - z is listed in shared clause  
      x = c;          // O.K.  - x is threadprivate  
                      //      - c has const-qualified type  
      z[i] = y;       // C3052 error - cannot reference i or y here  
  
      #pragma omp for firstprivate(y)  
         for (i=0; i<10 ; i++) {  
            z[i] = y;  // O.K. - i is the loop control variable  
                       // - y is listed in firstprivate clause  
          }  
       z[i] = y;   // Error - cannot reference i or y here  
   }  
}  

For more information on the default clause, see Section 2.7.2.5 on page 28.