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3. Fortran - 动态数组( Dynamic Arrays)

Fortran - 动态数组( Dynamic Arrays)

dynamic array是一个数组，其大小在编译时是未知的，但在执行时将是已知的。

使用属性allocatable声明动态数组。

例如，

real, dimension (:,:), allocatable :: darray    

但是，为了将内存分配给这样的数组，你必须提到数组的等级，即维度，你可以使用allocate函数。

allocate ( darray(s1,s2) )      

使用数组后，在程序中，应使用deallocate函数释放创建的内存

deallocate (darray)  

例子 (Example)

以下示例演示了上面讨论的概念。

program dynamic_array 
implicit none 
   !rank is 2, but size not known   
   real, dimension (:,:), allocatable :: darray    
   integer :: s1, s2     
   integer :: i, j     
   print*, "Enter the size of the array:"     
   read*, s1, s2      
   ! allocate memory      
   allocate ( darray(s1,s2) )      
   do i = 1, s1           
      do j = 1, s2                
         darray(i,j) = i*j               
         print*, "darray(",i,",",j,") = ", darray(i,j)           
      end do      
   end do      
   deallocate (darray)  
end program dynamic_array

编译并执行上述代码时，会产生以下结果 -

Enter the size of the array: 3,4
darray( 1 , 1 ) = 1.00000000    
darray( 1 , 2 ) = 2.00000000    
darray( 1 , 3 ) = 3.00000000    
darray( 1 , 4 ) = 4.00000000    
darray( 2 , 1 ) = 2.00000000    
darray( 2 , 2 ) = 4.00000000    
darray( 2 , 3 ) = 6.00000000    
darray( 2 , 4 ) = 8.00000000    
darray( 3 , 1 ) = 3.00000000    
darray( 3 , 2 ) = 6.00000000    
darray( 3 , 3 ) = 9.00000000    
darray( 3 , 4 ) = 12.0000000   

Use of Data 语句

data语句可用于初始化多个阵列，或用于阵列段初始化。

数据语句的语法是 -

data variable/list/...

例子 (Example)

以下示例演示了该概念 -

program dataStatement
implicit none
   integer :: a(5), b(3,3), c(10),i, j
   data a /7,8,9,10,11/ 
   data b(1,:) /1,1,1/ 
   data b(2,:)/2,2,2/ 
   data b(3,:)/3,3,3/ 
   data (c(i),i = 1,10,2) /4,5,6,7,8/ 
   data (c(i),i = 2,10,2)/5*2/
   Print *, 'The A array:'
   do j = 1, 5                
      print*, a(j)           
   end do 
   Print *, 'The B array:'
   do i = lbound(b,1), ubound(b,1)
      write(*,*) (b(i,j), j = lbound(b,2), ubound(b,2))
   end do
   Print *, 'The C array:' 
   do j = 1, 10                
      print*, c(j)           
   end do      
end program dataStatement

编译并执行上述代码时，会产生以下结果 -

 The A array:
           7
           8
           9
          10
          11
 The B array:
           1           1           1
           2           2           2
           3           3           3
 The C array:
           4
           2
           5
           2
           6
           2
           7
           2
           8
           2

Use of Where 语句

where语句允许您在表达式中使用数组的某些元素，具体取决于某些逻辑条件的结果。 如果给定条件为真，它允许在元素上执行表达式。

例子 (Example)

以下示例演示了该概念 -

program whereStatement
implicit none
   integer :: a(3,5), i , j
   do i = 1,3
      do j = 1, 5                
         a(i,j) = j-i          
      end do 
   end do
   Print *, 'The A array:'
   do i = lbound(a,1), ubound(a,1)
      write(*,*) (a(i,j), j = lbound(a,2), ubound(a,2))
   end do
   where( a<0 ) 
      a = 1 
   elsewhere
      a = 5
   end where
   Print *, 'The A array:'
   do i = lbound(a,1), ubound(a,1)
      write(*,*) (a(i,j), j = lbound(a,2), ubound(a,2))
   end do   
end program whereStatement

编译并执行上述代码时，会产生以下结果 -

 The A array:
           0           1           2           3           4
          -1           0           1           2           3
          -2          -1           0           1           2
 The A array:
           5           5           5           5           5
           1           5           5           5           5
           1           1           5           5           5