Components of Fortran MEX File
mexFunction Gateway Routine
The gateway routine is the entry point to the MEX
file. It is through this routine that MATLAB® accesses the rest of the routines in your MEX files. The name
of the gateway routine is
mexFunction. It takes the
place of the main program in your source code.
Naming the MEX File
The name of the source file containing
the name of your MEX file, and, hence, the name of the function you call in
MATLAB. Name your Fortran source file with an uppercase
.F file extension.
The file extension of the binary MEX file is platform-dependent. You find
the file extension using the
mexext function, which
returns the value for the current machine.
To ensure that your Fortran MEX file is platform independent, use an
.F file extension.
Fortran compilers assume source files using a lowercase
.f file extension have been preprocessed. On most
mex makes sure that the file is preprocessed
regardless of the file extension. However, on Apple
mex cannot force
The Fortran signature for
subroutine mexFunction(nlhs, plhs, nrhs, prhs) integer nlhs, nrhs mwpointer plhs(*), prhs(*)
Place this subroutine after your computational routine and any other subroutines in your source file.
The following table describes the parameters for
|Array of right-side input arguments.|
|Array of left-side output arguments.|
|Number of right-side arguments, or the size of the
|Number of left-side arguments, or the size of the
plhs as type
mwPointer, which means they point to MATLAB arrays. They are vectors that contain pointers to the
arguments of the MEX file.
You can think of the name
prhs as representing the
“parameters, right-hand side,” that is, the input parameters.
plhs represents the “parameters, left
side,” or output parameters.
Managing Input and Output Parameters
Input parameters (found in the
prhs array) are read-only;
do not modify them in your MEX file. Changing data in an input parameter can
produce undesired side effects.
You also must take care when using an input parameter to create output data
or any data used locally in your MEX file. If you want to copy an input
array into an output array, for example
plhs(1), call the
mxDuplicateArray function to make of copy of the
input array. For example:
plhs(1) = mxDuplicateArray(prhs(1))
For more information, see the troubleshooting topic Incorrectly Constructing a Cell or Structure mxArray.
For a list of functions to validate inputs to your subroutines, see the
Matrix Library category, Validate Fortran Data. The
mxIsClass function is a general-purpose way to
The computational routine contains the code for
performing the computations you want implemented in the binary MEX file.
Although not required, consider writing the gateway routine,
mexFunction, to call a computational routine. To
validate input parameters and to convert them into the types required by the
computational routine, use the
mexFunction code as a
If you write separate gateway and computational routines, you can combine
them into one source file or into separate files. If you use separate files,
the file containing
mexFunction must be the first
source file listed in the