Matlab与C/C++混合编程（mex文件）

阳光穿透心脏的1/2处 2022-08-27 11:41 215阅读 0赞

Matlab是一种矩阵语言，是为vector和matrix操作设计的，这两种类型的运算速度非常快，但是当涉及到大量的循环处理时，Matlab的速度就有点慢了。因此，Matlab提供了MEX脚本来使用C/C++函数以提高循环的运算速度。

现在我们来介绍一下如何编写相应的C/C++函数以生成对应的mexw32或mexw64文件。

MEX文件的编写和编译需要两个基本条件：一是必须按照Matlab应用程序接口组件设计；二是要有相应的C/C++编译器。这些我们先不谈，先来看看如何编写Source File。

我们以一个例子来讲——编写一个Mex文件来调用一个C函数：arrayProduct【这个函数实现一个常量与数组相乘】

**文件信息，非必需，可选：**

1: 
       2: /*==========================================================
       3:  * arrayProduct.c - example in MATLAB External Interfaces
       4:  *
       5:  * Multiplies an input scalar (multiplier) 
       6:  * times a 1xN matrix (inMatrix)
       7:  * and outputs a 1xN matrix (outMatrix)
       8:  *
       9:  * The calling syntax is:
      10:  *
      11:  *    outMatrix = arrayProduct(multiplier, inMatrix)
      12:  *
      13:  * This is a MEX-file for MATLAB.
      14:  * Copyright 2007-2012 The MathWorks, Inc.
      15:  *
      16:  *========================================================*/
      17: /* $Revision: 1.1.10.4 $ */
      18:

**添加头文件mex.h，该文件包含相应的MATLAB API函数声明。**

1: #include "mex.h"

**核心计算程序。**

1: /* The computational routine */
       2: void arrayProduct(double x, double *y, double *z, mwSize n)
       3: {
       4:     mwSize i;
       5:     /* multiply each element y by x */
       6:     for (i=0; i<n; i++) {
       7:         z[i] = x * y[i];
       8:     }
       9: }
      10:

**MEX文件的入口函数——mexFunction**

<table> 
 <tbody> 
  <tr> 
   <td>参数</td> 
   <td>描述</td> 
  </tr> 
  <tr> 
   <td>nlhs</td> 
   <td># of output arguments, or the size of the plhs array</td> 
  </tr> 
  <tr> 
   <td>plhs</td> 
   <td>Array of output arguments</td> 
  </tr> 
  <tr> 
   <td>nrhs</td> 
   <td># of input arguments, or the size of the prhs array</td> 
  </tr> 
  <tr> 
   <td>prhs</td> 
   <td>Array of input arguments.</td> 
  </tr> 
 </tbody> 
</table>

1: 
       2: /* The gateway function */
       3: void mexFunction( int nlhs, mxArray *plhs[],
       4:                   int nrhs, const mxArray *prhs[])
       5: {
       6:     double multiplier;              /* input scalar */
       7:     double *inMatrix;               /* 1xN input matrix */
       8:     size_t ncols;                   /* size of matrix */
       9:     double *outMatrix;              /* output matrix */
      10: 
      11:     /* check for proper number of arguments */
      12:     if(nrhs!=2) {
      13:         mexErrMsgIdAndTxt("MyToolbox:arrayProduct:nrhs","Two inputs required.");
      14:     }
      15:     if(nlhs!=1) {
      16:         mexErrMsgIdAndTxt("MyToolbox:arrayProduct:nlhs","One output required.");
      17:     }
      18:     /* make sure the first input argument is scalar */
      19:     if( !mxIsDouble(prhs[0]) || 
      20:          mxIsComplex(prhs[0]) ||
      21:          mxGetNumberOfElements(prhs[0])!=1 ) {
      22:         mexErrMsgIdAndTxt("MyToolbox:arrayProduct:notScalar","Input multiplier must be a scalar.");
      23:     }
      24:     
      25:     /* make sure the second input argument is type double */
      26:     if( !mxIsDouble(prhs[1]) || 
      27:          mxIsComplex(prhs[1])) {
      28:         mexErrMsgIdAndTxt("MyToolbox:arrayProduct:notDouble","Input matrix must be type double.");
      29:     }
      30:     
      31:     /* check that number of rows in second input argument is 1 */
      32:     if(mxGetM(prhs[1])!=1) {
      33:         mexErrMsgIdAndTxt("MyToolbox:arrayProduct:notRowVector","Input must be a row vector.");
      34:     }
      35:     
      36:     /* get the value of the scalar input  */
      37:     multiplier = mxGetScalar(prhs[0]);
      38: 
      39:     /* create a pointer to the real data in the input matrix  */
      40:     inMatrix = mxGetPr(prhs[1]);
      41: 
      42:     /* get dimensions of the input matrix */
      43:     ncols = mxGetN(prhs[1]);
      44: 
      45:     /* create the output matrix */
      46:     plhs[0] = mxCreateDoubleMatrix(1,(mwSize)ncols,mxREAL);
      47: 
      48:     /* get a pointer to the real data in the output matrix */
      49:     outMatrix = mxGetPr(plhs[0]);
      50: 
      51:     /* call the computational routine */
      52:     arrayProduct(multiplier,inMatrix,outMatrix,(mwSize)ncols);
      53: }