Fortran动态数组 - Fortran教程
动态数组是一种数组,其尺寸在编译时不知道,而是在执行时才已知/确定的。
动态数组的属性使用 allocatable 声明。 .
例如,
real, dimension (:,:), allocatable :: darray
数组的秩,即尺寸,必须提到但是,分配内存以这样的阵列,可以使用allocate函数。
allocate ( darray(s1,s2) )
该阵列使用后,在该程序中,所创建的存储器应该使用 deallocate 函数解除
deallocate (darray)
示例
下面的例子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
当上述代码被编译和执行时,它产生了以下结果:
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
使用data语句
data 语句可用于初始化多个阵列,或用于阵列部分的初始化。
data 语句的语法是:
data variable / list / ...
示例
下面的例子演示了这一概念:
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
当上述代码被编译和执行时,它产生了以下结果:
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
使用where语句
where语句可以使用数组中的某些元素在一个表达式,根据一些逻辑条件的结果。它允许表达的执行在一个元素上,如果给定的条件为真。
例子
下面的例子演示了这一概念:
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
当上述代码被编译和执行时,它产生了以下结果:
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