User`s manual

C MEX-Files
2-3
C MEX-Files
C MEX-files are built by using the mex script to compile your C source code with
additional calls to API routines.
The Components of a C MEX-File
The source code for a MEX-file consists of two distinct parts:
•A computational routine that contains the code for performing the
computations that you want implemented in the MEX-file. Computations
can be numerical computations as well as inputting and outputting data.
•A gateway routine that interfaces the computational routine with MATLAB
by the entry point
mexFunction and its parameters prhs, nrhs, plhs, nlhs,
where
prhs is an array of right-hand input arguments, nrhs is the number
of right-hand input arguments,
plhs is an array of left-hand output
arguments, and
nlhs is the number of left-hand output arguments. The
gateway calls the computational routine as a subroutine.
In the gateway routine, you can access the data in the
mxArray structure and
then manipulate this data in your C computational subroutine. For example,
the expression
mxGetPr(prhs[0]) returns a pointer of type double * to the real
data in the
mxArray pointed to by prhs[0]. You can then use this pointer like
any other pointer of type
double * in C. After calling your C computational
routine from the gateway, you can set a pointer of type
mxArray to the data it
returns. MATLAB is then able to recognize the output from your computational
routine as the output from the MEX-file.
The following C MEX Cycle figure shows how inputs enter a MEX-file, what
functions the gateway routine performs, and how outputs return to MATLAB.