MATLAB REAL-TIME WORKSHOP 7 - TARGET LANGUAGE COMPILER Uživatelský manuál stáhnout pdf (Strana 63)

C MEX-Files

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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.

1 2 ... 58 59 60 61 62 63 64 65 66 67 68 ... 407 408

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MATLAB REAL-TIME WORKSHOP 7 - TARGET LANGUAGE COMPILER Uživatelský manuál Strana 63