问题描述
是否有必要在任何其他代码之前声明数组维度?例如,我编写了以下简化示例代码:
Is it necessary to declare array dimensions before any other code? For example, I have written the following simplified example code:
PROGRAM mytest
IMPLICIT NONE
INTEGER :: i, j, k, mysum
! Let array c be a k-by-k**2 array
! Determine k within the program by some means...for example,
mysum=0
DO i=1, 3
mysum=mysum+1
END DO
k=mysum
REAL, DIMENSION(k, k**2) :: c
WRITE(*,*) "k=", k
WRITE(*,*) "k**2=", k**2
WRITE(*,*)
DO i=1,size(c,1)
WRITE(*,"(100(3X,F3.1))") (c(i,j), j=1,size(c,2))
END DO
END PROGRAM mytest
我想说明的一点是,我想创建一个数组 c
,即 k
-by-k**2
的大小,并且 k
仅由代码中的其他计算决定;k
一开始并不知道.
The point that I am trying to make is that I would like to create an array c
that is k
-by-k**2
in size, and k
is only determined by other computations within the code; k
is not known at the very beginning.
但是,上面的代码在编译时给了我以下错误信息:
But, the above code gives me the following error message at compile time:
mytest.f90:13.31:
REAL, DIMENSION(k, k**2) :: c
1
Error: Unexpected data declaration statement at (1)
我代码中的第 13 行是我最终声明 c
的那一行:REAL, DIMENSION(k, k**2) :: c
.
where line 13 in my code is the line where I finally declare c
: REAL, DIMENSION(k, k**2) :: c
.
另一方面,如果我改为声明 k
并预先指定其尺寸,
On the other hand, if I instead declare k
and specify its dimensions upfront,
PROGRAM mytest
IMPLICIT NONE
INTEGER :: i, j, k, mysum
REAL, DIMENSION(3,9) :: c
! Let array c be a k-by-k**2 array
! Determine k within the program by some means...for example,
mysum=0
DO i=1, 3
mysum=mysum+1
END DO
k=mysum
WRITE(*,*) "k=", k
WRITE(*,*) "k**2=", k**2
WRITE(*,*)
DO i=1,size(c,1)
WRITE(*,"(100(3X,F3.1))") (c(i,j), j=1,size(c,2))
END DO
END PROGRAM mytest
我得到了正确的输出:
k= 3
k**2= 9
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
但是,因为我事先不知道 k
,所以我无法在我的实际代码中做到这一点.有没有办法在不指定其维度的情况下最初声明"数组 c
,然后在 k
的值已知后指定维度?
But, since I don't know k
beforehand, I can't do exactly this in my actual code. Is there some way to "declare" the array c
initially, without specifying its dimensions, and then later specify the dimensions once the value of k
is known?
推荐答案
您想使用可分配数组:
PROGRAM mytest
IMPLICIT NONE
INTEGER :: i, j, k, mysum
REAL, DIMENSION(:,:), allocatable :: c !<- c is allocatable, rank 2
! Let array c be a k-by-k**2 array
! Determine k within the program by some means...for example,
mysum=0
DO i=1, 3
mysum=mysum+1
END DO
k=mysum
WRITE(*,*) "k=", k
WRITE(*,*) "k**2=", k**2
WRITE(*,*)
allocate(c(k,k**2)) ! <-- allocate array c with supplied shape
DO i=1,size(c,1)
WRITE(*,"(100(3X,F3.1))") (c(i,j), j=1,size(c,2))
END DO
deallocate(c) ! <-- deallocate when done
END PROGRAM mytest
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