對於 (OpenMP)

使完成的工作執行緒之間分割為在平行區域內的迴圈。

#pragma omp [parallel] for [clauses]
   for_statement

備註

其中，

• clause (選擇項)
  零個或多個子句。 請參閱 ＜ 備註 ＞ 一節清單所支援的子句的的。

• for_statement
  答： for 迴圈。 如果使用者的程式碼，就會產生未定義的行為迴圈變成 index 變數。

備註

的指示詞可支援下列 OpenMP 子句：

• firstprivate

• lastprivate

• [不等待

• 排序

• private

• 縮小

• 排程

如果平行指定了， clause可以任何子句所接受平行或的指示詞，除非 [不等待。

如需詳細資訊，請參閱 2.4.1 建構。

範例

// omp_for.cpp
// compile with: /openmp 
#include <stdio.h>
#include <math.h>
#include <omp.h>

#define NUM_THREADS 4
#define NUM_START 1
#define NUM_END 10

int main() {
   int i, nRet = 0, nSum = 0, nStart = NUM_START, nEnd = NUM_END;
   int nThreads = 0, nTmp = nStart + nEnd;
   unsigned uTmp = (unsigned((abs(nStart - nEnd) + 1)) * 
                               unsigned(abs(nTmp))) / 2;
   int nSumCalc = uTmp;

   if (nTmp < 0)
      nSumCalc = -nSumCalc;

   omp_set_num_threads(NUM_THREADS);

   #pragma omp parallel default(none) private(i) shared(nSum, nThreads, nStart, nEnd)
   {
      #pragma omp master
      nThreads = omp_get_num_threads();

      #pragma omp for
      for (i=nStart; i<=nEnd; ++i) {
            #pragma omp atomic
            nSum += i;
      }
   }

   if  (nThreads == NUM_THREADS) {
      printf_s("%d OpenMP threads were used.\n", NUM_THREADS);
      nRet = 0;
   }
   else {
      printf_s("Expected %d OpenMP threads, but %d were used.\n",
               NUM_THREADS, nThreads);
      nRet = 1;
   }

   if (nSum != nSumCalc) {
      printf_s("The sum of %d through %d should be %d, "
               "but %d was reported!\n",
               NUM_START, NUM_END, nSumCalc, nSum);
      nRet = 1;
   }
   else
      printf_s("The sum of %d through %d is %d\n",
               NUM_START, NUM_END, nSum);
}

請參閱

參考

OpenMP 指示詞