Assign variable length string to fixed length string

Question

I'm trying to bridge some C code into Fortran. However, I'm having trouble getting the variable length C strings returned by the C API into the fixed length strings required by the Fortran API.

Here's a reduced version of the code that won't compile - I get The shapes of the array expressions do not conform.

character*200 function getValueFromC() 
  use cbridge
  implicit none

  type(c_ptr) :: resultString
  integer(kind=c_int) :: resultLength
  character, pointer, dimension(:) :: string

  call c_bridge_getValue(bridge, resultString, resultLength)
  call c_f_pointer(resultString, string, (/ resultLength /) )
  getValueFromC = string
  call c_bridge_releaseString(resultString)
end function getValueFromC

cbridge is just the module containing the c_bridge_getValue() and c_bridge_releaseString definitions, and the bridge pointer (just a void*)

c_bridge_getValue() just mallocs up a new string and returns it, and c_bridge_releaseString() frees the memory.

So my question is, what do I need to do to assign the string variable to the getValueFromC?

Always use tag fortran for Fortran questions. And your code is Fortran2003, so the fortran90 tag was inappropriate. — Vladimir F Героям слава
– Vladimir F Героям слава, Commented Mar 8, 2016 at 9:30

Michael Anderson · Accepted Answer · 2016-03-08 08:50:50Z

1

One solution is to loop and assign to the string slices. I've not verified that this is 100% right, but it compiles for me...

character*200 function getValueFromC() 
  use cbridge
  implicit none

  type(c_ptr) :: resultString
  integer(kind=c_int) :: resultLength
  character, pointer, dimension(:) :: string

  call c_bridge_getValue(bridge, resultString, resultLength)
  call c_f_pointer(resultString, string, (/ resultLength /) )
  do i = 1, min(200, resultLength)
    getValueFromC(i:i) = string(i)
  end do
  call c_bridge_releaseString(resultString)
end function getValueFromC

answered Mar 8, 2016 at 8:50

Michael Anderson

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2 Comments

Vladimir F Героям слава Over a year ago

That is correct, the problem is that getValueFromC is a character string (scalar) and string is an array of characters of length 1.

haraldkl Over a year ago

Yes, I'd say this is a valid solution, I am doing the same: bitbucket.org/apesteam/aotus/src/…

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