Matlab C混合编程
- #include "mex.h"
- void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
- {
- mexPrintf("hello,world!\n");
- }
假设你把hello.c放在了C:\TEST\下，在Matlab里用CD C:\TEST\ 将当前目录改为C:\TEST\（注意，仅将C:\TEST\加入搜索路径是没有用的）。现在敲：
mex hello.c
如果一切顺利，编译应该在出现编译器提示信息后正常退出。如果你已将C:\TEST\加入了搜索路径，现在键入hello，程序会在屏幕上打出一行： hello,world!
nlhs：输出参数数目
plhs：指向输出参数的指针
nrhs：输入参数数目
例如，使用
[a,b]=test(c,d,e)
调用mex函数test时，传给test的这三个参数分别是 prhs[0]=c ，prhs[1]=d ，prhs[2]=e
当函数返回时，将会把你放在plhs[0]，plhs[1]里的地址赋给a和b，达到返回数据的目的。
细心的你也许已经注意到，prhs[i]和plhs[i]都是指向类型mxArray类型数据的指针。 这个类型是在mex.h中定义的，事实上，在Matlab里大多数数据都是以这种类型存在。当然还有其他的数据类型，可以参考Apiguide.pdf里的介绍。
- //hello.c 2.0
- #include "mex.h"
- void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
- {
- int i;
- i=mxGetScalar(prhs[0]);
- if(i==1)
- mexPrintf("hello,world!\n");
- else
- mexPrintf("大家好！\n");
- }
将这个程序编译通过后，执行hello(1),屏幕上会打出：
hello,world!
而hello(0)将会得到：
大家好！
现在，程序hello已经可以根据输入参数来给出相应的屏幕输出。在这个程序里，除了用到了屏幕输出函数mexPrintf（用法跟c里的printf函数几乎完全一样）外，还用到了一个函数：mxGetScalar，调用方式如下：
i=mxGetScalar(prhs[0]);
"Scalar"就是标量的意思。在Matlab里数据都是以数组的形式存在的，mxGetScalar的作用就是把通过prhs[0]传递进来的mxArray类型的指针指向的数据（标量）赋给C程序里的变量。这个变量本来应该是double类型的，通过强制类型转换赋给了整形变量i。既然有标量，显然还应该有矢量，否则矩阵就没法传了。看下面的程序：
- //hello.c 2.1
- #include "mex.h"
- void mexFunction(int nlhs, mxArray *plhs[],
- int nrhs, const mxArray *prhs[])
- {
- int *i;
- i=mxGetPr(prhs[0]); //prhs是一个指针数组（每一个是一个指针），所以返回一个指针
- if(i[0]==1)
- mexPrintf("hello,world!\n");
- else
- mexPrintf("大家好！\n");
- }
这样，就通过mxGetPr函数从指向mxArray类型数据的prhs[0]获得了指向double类型的指针。
但是，还有个问题，如果输入的不是单个的数据，而是向量或矩阵，那该怎么处理呢 ？通过mxGetPr只能得到指向这个矩阵的指针，如果我们不知道这个矩阵的确切大小，就 没法对它进行计算。
为了解决这个问题，Matlab提供了两个函数mxGetM和mxGetN来获得传进来参数的行数 和列数。下面例程的功能很简单，就是获得输入的矩阵，把它在屏幕上显示出来：
- //show.c 1.0
- #include "mex.h"
- #include "mex.h"
- void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
- {
- double *data;
- int M,N;
- int i,j;
- data=mxGetPr(prhs[0]); //获得指向矩阵的指针
- M=mxGetM(prhs[0]); //获得矩阵的行数
- N=mxGetN(prhs[0]); //获得矩阵的列数
- for(i=0;i<M;i++)
- { for(j=0;j<N;j++)
- mexPrintf("%4.3f ",data[j*M+i]);
- mexPrintf("\n");
- }
- }
编译完成后，用下面的命令测试一下：
- a=1:10;
- b=[a;a+1];
- show(a)
- show(b)
- // 获取维度个数
- numOfDim = mxGetNumberOfDimensions(pArray);
- // 获取维度数组
- Dims = mxGetDimensions(pArray);
需要注意的是，在Matlab里，矩阵第一行是从1开始的，而在C语言中，第一行的序数为零，Matlab里的矩阵元素b(i,j)在传递到C中的一维数组data后对应于data[j*M+i] 。 输入数据是在函数调用之前已经在Matlab里申请了内存的，由于mex函数与Matlab共用同一个地址空间，因而在prhs[]里传递指针就可以达到参数传递的目的。但是，输出参数却需要在mex函数内申请到内存空间，才能将指针放在plhs[]中传递出去。由于返回指针类型必须是mxArray，所以Matlab专门提供了一个函数：mxCreateDoubleMatrix来实现内存的申请，函数原型如下：
mxArray *mxCreateDoubleMatrix(int m, int n, mxComplexity ComplexFlag)
m：待申请矩阵的行数
n：待申请矩阵的列数
为矩阵申请内存后，得到的是mxArray类型的指针，就可以放在plhs[]里传递回去了。但是对这个新矩阵的处理，却要在函数内完成，这时就需要用到前面介绍的mxGetPr。使用 mxGetPr获得指向这个矩阵中数据区的指针（double类型）后，就可以对这个矩阵进行各种操作和运算了。下面的程序是在上面的show.c的基础上稍作改变得到的，功能是将输出处理后的元素：
- //reverse.c 1.0
- #include "mex.h"
- void mexFunction(int nlhs, mxArray *plhs[],
- int nrhs, const mxArray *prhs[])
- {
- double *inData;
- double *outData;
- int M,N;
- int i,j;
- inData=mxGetPr(prhs[0]);
- M=mxGetM(prhs[0]);
- N=mxGetN(prhs[0]);
- plhs[0]=mxCreateDoubleMatrix(M,N,mxREAL);
- outData=mxGetPr(plhs[0]);
- for(i=0;i<M;i++)
- for(j=0;j<N;j++)
- outData[j*M+i]=inData[(N-1-j)*M+i];
- }
当然，Matlab里使用到的并不是只有double类型这一种矩阵，还有字符串类型、稀疏矩阵、结构类型矩阵等等，并提供了相应的处理函数。本文用到编制mex程序中最经常遇到的一些函数，其余的详细情况清参考Apiref.pdf。
通过前面两部分的介绍，大家对参数的输入和输出方法应该有了基本的了解。具备了这些知识，就能够满足一般的编程需要了。但这些程序还有些小的缺陷，以前面介绍的re由于前面的例程中没有对输入、输出参数的数目及类型进行检查，导致程序的容错性很差，以下程序则容错性较好
- #include "mex.h"
- void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
- {
- double *inData;
- double *outData;
- int M,N;
- //异常处理
- //异常处理
- if(nrhs!=1)
- mexErrMsgTxt("USAGE: b=reverse(a)\n");
- if(!mxIsDouble(prhs[0]))
- mexErrMsgTxt("the Input Matrix must be double!\n");
- inData=mxGetPr(prhs[0]);
- M=mxGetM(prhs[0]);
- N=mxGetN(prhs[0]);
- plhs[0]=mxCreateDoubleMatrix(M,N,mxREAL);
- outData=mxGetPr(plhs[0]);
- for(i=0;i<M;i++)
- for(j=0;j<N;j++)
- outData[j*M+i]=inData[(N-1-j)*M+i];
- }
在上面的异常处理中，使用了两个新的函数：mexErrMsgTxt和mxIsDouble。MexErrMsgTxt在给出出错提示的同时退出当前程序的运行。MxIsDouble则用于判断mxArray中的数据是否double类型。当然Matlab还提供了许多用于判断其他数据类型的函数，这里不加详述。
需要说明的是，Matlab提供的API中，函数前缀有mex-和mx-两种。带mx-前缀的大多是对mxArray数据进行操作的函数，如mxIsDouble,mxCreateDoubleMatrix等等。而带mx前缀的则大多是与Matlab环境进行交互的函数，如mexPrintf，mxErrMsgTxt等等。了解了这一点，对在Apiref.pdf中查找所需的函数很有帮助。
MX Matrix Library
| mwIndex (C and Fortran) |
Type for index values |
| mwPointer (Fortran) |
Pointer type for platform |
| mwSignedIndex (C and Fortran) |
Signed integer type for size values |
| mwSize (C and Fortran) |
Type for size values |
| mxAddField (C and Fortran) |
Field to structure array |
| mxArray (C and Fortran) |
Type for MATLAB array |
| mxArrayToString (C) |
Convert array to string |
| mxAssert (C) |
Check assertion value for debugging purposes |
| mxAssertS (C) |
Check assertion value without printing assertion text |
| mxCalcSingleSubscript (C and Fortran) |
Offset from first element to desired element |
| mxCalloc (C and Fortran) |
Allocate dynamic memory for array using MATLAB memory manager |
| mxChar (C) |
Type for string array |
| mxClassID (C) |
Enumerated value identifying class of array |
| mxClassIDFromClassName (Fortran) |
Identifier corresponding to class |
| mxComplexity (C) |
Flag specifying whether array has imaginary components |
| mxCopyCharacterToPtr (Fortran) |
CHARACTER values from Fortran array to pointer array |
| mxCopyComplex16ToPtr (Fortran) |
COMPLEX*16 values from Fortran array to pointer array |
| mxCopyComplex8ToPtr (Fortran) |
COMPLEX*8 values from Fortran array to pointer array |
| mxCopyInteger1ToPtr (Fortran) |
INTEGER*1 values from Fortran array to pointer array |
| mxCopyInteger2ToPtr (Fortran) |
INTEGER*2 values from Fortran array to pointer array |
| mxCopyInteger4ToPtr (Fortran) |
INTEGER*4 values from Fortran array to pointer array |
| mxCopyPtrToCharacter (Fortran) |
CHARACTER values from pointer array to Fortran array |
| mxCopyPtrToComplex16 (Fortran) |
COMPLEX*16 values from pointer array to Fortran array |
| mxCopyPtrToComplex8 (Fortran) |
COMPLEX*8 values from pointer array to Fortran array |
| mxCopyPtrToInteger1 (Fortran) |
INTEGER*1 values from pointer array to Fortran array |
| mxCopyPtrToInteger2 (Fortran) |
INTEGER*2 values from pointer array to Fortran array |
| mxCopyPtrToInteger4 (Fortran) |
INTEGER*4 values from pointer array to Fortran array |
| mxCopyPtrToPtrArray (Fortran) |
Pointer values from pointer array to Fortran array |
| mxCopyPtrToReal4 (Fortran) |
REAL*4 values from pointer array to Fortran array |
| mxCopyPtrToReal8 (Fortran) |
REAL*8 values from pointer array to Fortran array |
| mxCopyReal4ToPtr (Fortran) |
REAL*4 values from Fortran array to pointer array |
| mxCopyReal8ToPtr (Fortran) |
REAL*8 values from Fortran array to pointer array |
| mxCreateCellArray (C and Fortran) |
Unpopulated N-D cell array |
| mxCreateCellMatrix (C and Fortran) |
Unpopulated 2-D cell array |
| mxCreateCharArray (C and Fortran) |
Unpopulated N-D string array |
| mxCreateCharMatrixFromStrings (C and Fortran) |
Create populated 2-D string array |
| mxCreateDoubleMatrix (C and Fortran) |
2-D, double-precision, floating-point array initialized to 0 |
| mxCreateDoubleScalar (C and Fortran) |
Scalar, double-precision array initialized to specified value |
| mxCreateLogicalArray (C) |
N-D logical array initialized to false |
| mxCreateLogicalMatrix (C) |
2-D, logical array initialized to false |
| mxCreateLogicalScalar (C) |
Scalar, logical array |
| mxCreateNumericArray (C and Fortran) |
Unpopulated N-D numeric array |
| mxCreateNumericMatrix (C and Fortran) |
Numeric matrix initialized to 0 |
| mxCreateSparse (C and Fortran) |
2-D unpopulated sparse array |
| mxCreateSparseLogicalMatrix (C) |
Unpopulated 2-D, sparse, logical array |
| mxCreateString (C and Fortran) |
Create 1-by-N array initialized to specified string |
| mxCreateStructArray (C and Fortran) |
Unpopulated N-D structure array |
| mxCreateStructMatrix (C and Fortran) |
Unpopulated 2-D structure array |
| mxDestroyArray (C and Fortran) |
Free dynamic memory allocated by MXCREATE* functions |
| mxDuplicateArray (C and Fortran) |
Make deep copy of array |
| mxFree (C and Fortran) |
Free dynamic memory allocated by MXCALLOC, MXMALLOC, or MXREALLOC functions |
| mxGetCell (C and Fortran) |
Contents of array cell |
| mxGetChars (C) |
Pointer to character array data |
| mxGetClassID (C and Fortran) |
Class of array |
| mxGetClassName (C and Fortran) |
Class of array as string |
| mxGetData (C and Fortran) |
Pointer to real data |
| mxGetDimensions (C and Fortran) |
Pointer to dimensions array |
| mxGetElementSize (C and Fortran) |
Number of bytes required to store each data element |
| mxGetEps (C and Fortran) |
Value of EPS |
| mxGetField (C and Fortran) |
Field value, given field name and index, into structure array |
| mxGetFieldByNumber (C and Fortran) |
Field value, given field number and index, into structure array |
| mxGetFieldNameByNumber (C and Fortran) |
Field name, given field number, in structure array |
| mxGetFieldNumber (C and Fortran) |
Field number, given field name, in structure array |
| mxGetImagData (C and Fortran) |
Pointer to imaginary data of array |
| mxGetInf (C and Fortran) |
Value of infinity |
| mxGetIr (C and Fortran) |
Sparse matrix IR array |
| mxGetJc (C and Fortran) |
Sparse matrix JC array |
| mxGetLogicals (C) |
Pointer to logical array data |
| mxGetM (C and Fortran) |
Number of rows in array |
| mxGetN (C and Fortran) |
Number of columns in array |
| mxGetNaN (C and Fortran) |
Value of NaN (Not-a-Number) |
| mxGetNumberOfDimensions (C and Fortran) |
Number of dimensions in array |
| mxGetNumberOfElements (C and Fortran) |
Number of elements in array |
| mxGetNumberOfFields (C and Fortran) |
Number of fields in structure array |
| mxGetNzmax (C and Fortran) |
Number of elements in IR, PR, and PI arrays |
| mxGetPi (C and Fortran) |
Imaginary data elements in array of type DOUBLE |
| mxGetPr (C and Fortran) |
Real data elements in array of type DOUBLE |
| mxGetProperty (C and Fortran) |
Value of public property of MATLAB object |
| mxGetScalar (C and Fortran) |
Real component of first data element in array |
| mxGetString (C and Fortran) |
String array to C-style string |
| mxIsCell (C and Fortran) |
Determine whether input is cell array |
| mxIsChar (C and Fortran) |
Determine whether input is string array |
| mxIsClass (C and Fortran) |
Determine whether array is member of specified class |
| mxIsComplex (C and Fortran) |
Determine whether data is complex |
| mxIsDouble (C and Fortran) |
Determine whether mxArray represents data as double-precision, floating-point numbers |
| mxIsEmpty (C and Fortran) |
Determine whether array is empty |
| mxIsFinite (C and Fortran) |
Determine whether input is finite |
| mxIsFromGlobalWS (C and Fortran) |
Determine whether array was copied from MATLAB global workspace |
| mxIsInf (C and Fortran) |
Determine whether input is infinite |
| mxIsInt16 (C and Fortran) |
Determine whether array represents data as signed 16-bit integers |
| mxIsInt32 (C and Fortran) |
Determine whether array represents data as signed 32-bit integers |
| mxIsInt64 (C and Fortran) |
Determine whether array represents data as signed 64-bit integers |
| mxIsInt8 (C and Fortran) |
Determine whether array represents data as signed 8-bit integers |
| mxIsLogical (C and Fortran) |
Determine whether array is of type mxLogical |
| mxIsLogicalScalar (C) |
Determine whether scalar array is of type mxLogical |
| mxIsLogicalScalarTrue (C) |
Determine whether scalar array of type mxLogical is true |
| mxIsNaN (C and Fortran) |
Determine whether input is NaN (Not-a-Number) |
| mxIsNumeric (C and Fortran) |
Determine whether array is numeric |
| mxIsSingle (C and Fortran) |
Determine whether array represents data as single-precision, floating-point numbers |
| mxIsSparse (C and Fortran) |
Determine whether input is sparse array |
| mxIsStruct (C and Fortran) |
Determine whether input is structure array |
| mxIsUint16 (C and Fortran) |
Determine whether array represents data as unsigned 16-bit integers |
| mxIsUint32 (C and Fortran) |
Determine whether array represents data as unsigned 32-bit integers |
| mxIsUint64 (C and Fortran) |
Determine whether array represents data as unsigned 64-bit integers |
| mxIsUint8 (C and Fortran) |
Determine whether array represents data as unsigned 8-bit integers |
| mxLogical (C) |
Type for logical array |
| mxMalloc (C and Fortran) |
Allocate dynamic memory using MATLAB memory manager |
| mxRealloc (C and Fortran) |
Reallocate dynamic memory using MATLAB memory manager |
| mxRemoveField (C and Fortran) |
Remove field from structure array |
| mxSetCell (C and Fortran) |
Value of one cell of array |
| mxSetClassName (C) |
Convert structure array to MATLAB object array |
| mxSetData (C and Fortran) |
Set pointer to data |
| mxSetDimensions (C and Fortran) |
Modify number of dimensions and size of each dimension |
| mxSetField (C and Fortran) |
Set structure array field, given structure field name and array index |
| mxSetFieldByNumber (C and Fortran) |
Set structure array field, given field number and index |
| mxSetImagData (C and Fortran) |
Imaginary data pointer for array |
| mxSetIr (C and Fortran) |
IR array of sparse array |
| mxSetJc (C and Fortran) |
JC array of sparse array |
| mxSetM (C and Fortran) |
Number of rows in array |
| mxSetN (C and Fortran) |
Set number of columns in array |
| mxSetNzmax (C and Fortran) |
Set storage space for nonzero elements |
| mxSetPi (C and Fortran) |
Set new imaginary data for array |
| mxSetPr (C and Fortran) |
Set new real data for array |
| mxSetProperty (C and Fortran) |
Set value of public property of MATLAB object |
MEX Library
| mexAtExit (C and Fortran) |
Register function to call when MEX-function cleared or MATLAB software terminates |
| mexCallMATLAB (C and Fortran) |
Call MATLAB function, user-defined function, or MEX-file |
| mexCallMATLABWithTrap (C and Fortran) |
Call MATLAB function, user-defined function, or MEX-file and capture error information |
| mexErrMsgIdAndTxt (C and Fortran) |
Display error message with identifier and return to MATLAB prompt |
| mexErrMsgTxt (C and Fortran) |
Display error message and return to MATLAB prompt |
| mexEvalString (C and Fortran) |
Execute MATLAB command in caller workspace |
| mexEvalStringWithTrap (C and Fortran) |
Execute MATLAB command in caller workspace and capture error information |
| mexFunction (C and Fortran) |
Entry point to C/C++ or Fortran MEX-file |
| mexFunctionName (C and Fortran) |
Name of current MEX-function |
| mexGet (C) |
Value of specified Handle Graphics property |
| mexGetVariable (C and Fortran) |
Copy of variable from specified workspace |
| mexGetVariablePtr (C and Fortran) |
Read-only pointer to variable from another workspace |
| mexIsGlobal (C and Fortran) |
Determine whether variable has global scope |
| mexIsLocked (C and Fortran) |
Determine whether MEX-file is locked |
| mexLock (C and Fortran) |
Prevent clearing MEX-file from memory |
| mexMakeArrayPersistent (C and Fortran) |
Make array persist after MEX-file completes |
| mexMakeMemoryPersistent (C and Fortran) |
Make memory allocated by MATLAB software persist after MEX-function completes |
| mexPrintf (C and Fortran) |
ANSI C PRINTF-style output routine |
| mexPutVariable (C and Fortran) |
Array from MEX-function into specified workspace |
| mexSet (C) |
Set value of specified Handle Graphics property |
| mexSetTrapFlag (C and Fortran) |
Control response of MEXCALLMATLAB to errors |
| mexUnlock (C and Fortran) |
Allow clearing MEX-file from memory |
| mexWarnMsgIdAndTxt (C and Fortran) |
Warning message with identifier |
| mexWarnMsgTxt (C and Fortran) |
Warning message |
参考：
http://blog.sciencenet.cn/blog-620659-579885.html
http://blog.csdn.net/raodotcong/article/details/6295859