Passing Arrays of Strings :: Creating Fortran MEX-Files (External Interfaces)

External Interfaces

Passing Arrays of Strings

Passing arrays of strings adds a slight complication to the example in the previous section, Passing Strings. Because MATLAB stores elements of a matrix by column instead of by row, it is essential that the size of the string array be correctly defined in the Fortran MEX-file. The key point is that the row and column sizes as defined in MATLAB must be reversed in the Fortran MEX-file. Consequently, when returning to MATLAB, the output matrix must be transposed.

This example places a string array/character matrix into MATLAB as output arguments rather than placing it directly into the workspace. Inside MATLAB, call this function by typing

```
passstr;
```

You will get the matrix mystring of size 5-by-15. There are some manipulations that need to be done here. The original string matrix is of the size 5-by-15. Because of the way MATLAB reads and orients elements in matrices, the size of the matrix must be defined as M=15 and N=5 from the MEX-file. After the matrix is put into MATLAB, the matrix must be transposed.

C==============================================================
=
C     passstr.f
C     Example for illustrating how to pass a character matrix 
C     from Fortran to MATLAB.
C 
C     Passes a string array/character matrix into MATLAB as 
C     output arguments rather than placing it directly into the
C     workspace.
C      
C     This is a MEX-file for MATLAB.
C     Copyright (c) 1984-2000 The MathWorks, Inc.
C     $Revision: 1.11 $
C==============================================================
=

C     The gateway routine
      subroutine mexFunction(nlhs, plhs, nrhs, prhs)

      integer mxCreateString
      integer plhs(*), prhs(*)
      integer nlhs, nrhs, p_str
      integer i
      character*75 thestring
      character*15 string(5)

C     Create the strings to be passed into MATLAB.
      string(1) = 'MATLAB         '
      string(2) = 'The Scientific '
      string(3) = 'Computing      '
      string(4) = 'Environment    '
      string(5) = '   by TMW, Inc.'
      
C     Concatenate the set of 5 strings into a long string.
      thestring = string(1)
      do 10 i=2,6
         thestring = thestring(:((i-1)*15)) // string(i)
 10   continue
      
C     Create the string matrix to be passed into MATLAB. 
C     Set the matrix size to be M=15 and N=5.
      p_str = mxcreatestring(thestring)
      call mxSetM(p_str, 15)
      call mxSetN(p_str, 5)
      
C     Transpose the resulting matrix in MATLAB.
      call mexCallMATLAB(1, plhs, 1, p_str, 'transpose')

      return
      end

Typing

```
passstr
```

at the MATLAB prompt produces this result

ans =

MATLAB         
The Scientific 
Computing      
Environment    
   by TMW, Inc.

Passing Strings Passing Matrices