Return an array of strings of different length in Fortran

问题

I would like to create a type to contain an array of strings in Fortran without explicitly assigning lengths so I can return it from a function.

The following is my type:

type returnArr
    Character (*), dimension(4)  :: array
end type returnArr

The following is the function's signature:

type(returnArr) FUNCTION process(arr, mean, stdDev) result(j)

The following is where I try set the result:

j%array(1)= "Test"

But all I get is the following error:

Error: Character length of component ‘array’ needs to be a constant specification expression at (1)

How can I declare the type so that the strings may be of different length?

回答1:

A character component of a derived type may have either an explicit length, or it may have its length deferred. This latter is how one changes its value (by any of a number of means). It is also necessary to allow the flexibility of different lengths in an array of the derived type.

However, using len=* is not the correct way to say "deferred length" (it is "assumed length"). Instead, you may use len=: and make the component allocatable (or a pointer):

type returnArr
  Character (:), allocatable  :: char
end type returnArr

Then one may have an array of returnArr objects:

function process(arr, mean, stdDev) result(j)
  type(returnArr) :: j(4)
end function

Assignment such as as

  j(1)%char = "Test"

then relies on automatic allocation of the component char.

Note that now the function result is an array of that container type. We cannot do

function process(arr, mean, stdDev) result(j)
  character(:), allocatable :: j(:)
end function

and allocate j(1) to a length different from j(2) (etc.).

Similarly

type returnArr
  Character (:), allocatable  :: char(:)
end type returnArr

doesn't allow those char component elements to be of different lengths.

来源：https://stackoverflow.com/questions/51968735/return-an-array-of-strings-of-different-length-in-fortran

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arrays

string

types

fortran

character