Fortran 简明教程
Fortran - Dynamic Arrays
一个 dynamic array 是一个其大小在编译时未知但会在执行时已知的数组。
A dynamic array is an array, the size of which is not known at compile time, but will be known at execution time.
使用特性 allocatable 声明动态数组。
Dynamic arrays are declared with the attribute allocatable.
例如，
For example,
real, dimension (:,:), allocatable :: darray必须声明数组的秩，即维度，但是，要为这样的数组分配内存，请使用 allocate 函数。
The rank of the array, i.e., the dimensions has to be mentioned however, to allocate memory to such an array, you use the allocate function.
allocate ( darray(s1,s2) )在程序中使用数组后，应使用 deallocate 函数释放所创建的内存。
After the array is used, in the program, the memory created should be freed using the deallocate function
deallocate (darray)Example
以下示例展示了上面讨论的概念。
The following example demonstrates the concepts discussed above.
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后，将产生以下结果 −
When the above code is compiled and executed, it produces the following result −
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 ) = 12.0000000Use of Data Statement
使用 data 语句可以初始化多个数组，或者用于数组部分初始化。
The data statement can be used for initialising more than one array, or for array section initialisation.
数据语句的语法为 −
The syntax of data statement is −
data variable / list / ...Example
以下示例演示了此概念 −
The following example demonstrates the concept −
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后，将产生以下结果 −
When the above code is compiled and executed, it produces the following result −
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
2Use of Where Statement
where 语句允许你根据逻辑条件的结果，在表达式中使用数组的某些元素。如果给定的条件为真，它允许针对元素执行表达式。
The where statement allows you to use some elements of an array in an expression, depending on the outcome of some logical condition. It allows the execution of the expression, on an element, if the given condition is true.
Example
以下示例演示了此概念 −
The following example demonstrates the concept −
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后，将产生以下结果 −
When the above code is compiled and executed, it produces the following result −
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