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A.22 Using the default(none) Clause 

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 on page 28.