External Interfaces/API

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: 1.9 $
  C==============================================================
  =
  
  C     The gateway routine
        subroutine mexFunction(nlhs, plhs, nrhs, prhs)
  C--------------------------------------------------------------
  C     (pointer) Replace integer by integer*8 on the DEC Alpha  
  C     platform.
  
        integer plhs(*), prhs(*)
        integer p_str, mxCreateString
  C--------------------------------------------------------------
  
        integer nlhs, nrhs
        integer i
        character*75 thestring
        character*15 string(5)
  
  C     Create the string to 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