Matrices in C S-Functions
MX Array Manipulation
S-functions can manipulate mxArrays using
the standard MATLAB API functions. (See MX Array Manipulation in
the MATLAB C and Fortran API Reference pages for a complete list
of functions.) In general, if your S-function is declared exception
free by passing the SS_OPTION_EXCEPTION_FREE_CODE option
to ssSetOptions (see Exception Free Code in Error Handling), it should avoid MATLAB API
functions that throw exceptions (i.e., long jump), such as mxCreateDoubleMatrix.
Otherwise, the S-function can use any of the listed functions.
The Real-Time Workshop product
supports a subset of the mxArray manipulation functions
when generating noninlined code for an S-function. For a list of supported
functions, see Writing Noninlined S-Functions in the Real-Time Workshop User's
Guide.
Calls to the macro ssGetSFcnParam return
a pointer to an mxArray, which can be used with
the mxArray manipulation functions. If your S-function
contains S-function parameters, use the mxArray manipulation
functions in the mdlCheckParameters method to check
the S-function parameter values. See the S-function sfun_runtime3.c for
an example
In this S-function, the following lines check that the first
S-function parameter is a character array with a length greater than
or equal to two.
if (!mxIsChar(ssGetSFcnParam(S, 0)) ||
(nu=mxGetNumberOfElements(ssGetSFcnParam(S, 0))) < 2) {
ssSetErrorStatus(S,"1st parameter to S-function must be a "
"string of at least 2 '+' and '-' characters");
return;
}Back to Top
Memory Allocation
When you create an S-function, you might need to allocate memory
for each instance of your S-function. The standard MATLAB API
memory allocation routines mxCalloc and mxFree should
not be used with C MEX S-functions, because these routines are designed
to be used with MEX-files that are called from the MATLAB environment
and not the Simulink environment. The correct approach for allocating
memory is to use the stdlib.h library routines calloc and free.
In mdlStart, allocate and initialize the memory
UD *ptr = (UD *)calloc(1,sizeof(UD));
where UD, in this example, is a data structure
defined at the beginning of the S-function. Then, place the pointer
to it either in the pointer work vector
ssSetPWorkValue(S, 0, ptr);
or attach it as user data.
ssSetUserData(S,ptr);
In mdlTerminate, free the allocated memory.
For example, if the pointer was stored in the user data
UD *prt = ssGetUserData(S);
free(prt);
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