Matlab C混合编程
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假設你把hello.c放在了C:\TEST\下，在Matlab里用CD C:\TEST\ 將當前目錄改為C:\TEST\（注意，僅將C:\TEST\加入搜索路徑是沒有用的）。現在敲：
mex hello.c
?? 如果一切順利，編譯應該在出現編譯器提示信息后正常退出。如果你已將C:\TEST\加入了搜索路徑，現在鍵入hello，程序會在屏幕上打出一行：hello,world! 看看C\TEST\目錄下，你會發現多了一個文件：HELLO.DLL。說明Mex函數已經完成，編譯成功 ? 接口函數規范mexFunction介紹 void?mexFunction(int?nlhs,?mxArray?*plhs[],?int?nrhs,?const?mxArray?*prhs[])
nlhs：輸出參數數目?
plhs：指向輸出參數的指針?
nrhs：輸入參數數目?
例如，使用
[a,b]=test(c,d,e)
調用mex函數test時，傳給test的這三個參數分別是?prhs[0]=c?，prhs[1]=d?，prhs[2]=e?
當函數返回時，將會把你放在plhs[0]，plhs[1]里的地址賦給a和b，達到返回數據的目的。??
細心的你也許已經注意到，prhs[i]和plhs[i]都是指向類型mxArray類型數據的指針。?這個類型是在mex.h中定義的，事實上，在Matlab里大多數數據都是以這種類型存在。當然還有其他的數據類型，可以參考Apiguide.pdf里的介紹。 為了讓大家能更直觀地了解參數傳遞的過程，我們把hello.c改寫一下，使它能根據輸?入參數的變化給出不同的屏幕輸出：
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將這個程序編譯通過后，執行hello(1),屏幕上會打出：?
??????????hello,world!?
而hello(0)將會得到：?
???????????大家好！?
現在，程序hello已經可以根據輸入參數來給出相應的屏幕輸出。在這個程序里，除了用到了屏幕輸出函數mexPrintf（用法跟c里的printf函數幾乎完全一樣）外，還用到了一個函數：mxGetScalar，調用方式如下：?
i=mxGetScalar(prhs[0]);?
"Scalar"就是標量的意思。在Matlab里數據都是以數組的形式存在的，mxGetScalar的作用就是把通過prhs[0]傳遞進來的mxArray類型的指針指向的數據（標量）賦給C程序里的變量。這個變量本來應該是double類型的，通過強制類型轉換賦給了整形變量i。既然有標量，顯然還應該有矢量，否則矩陣就沒法傳了。看下面的程序：?
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這樣，就通過mxGetPr函數從指向mxArray類型數據的prhs[0]獲得了指向double類型的指針。
但是，還有個問題，如果輸入的不是單個的數據，而是向量或矩陣，那該怎么處理呢?？通過mxGetPr只能得到指向這個矩陣的指針，如果我們不知道這個矩陣的確切大小，就?沒法對它進行計算。?
為了解決這個問題，Matlab提供了兩個函數mxGetM和mxGetN來獲得傳進來參數的行數?和列數。下面例程的功能很簡單，就是獲得輸入的矩陣，把它在屏幕上顯示出來：?
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編譯完成后，用下面的命令測試一下：?
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還有就是若是數據不是二維的，可以通過下面的函數獲得數據的維度個數（向量：1，矩陣：2，...）以及維度數組。
需要注意的是，在Matlab里，矩陣第一行是從1開始的，而在C語言中，第一行的序數為零，Matlab里的矩陣元素b(i,j)在傳遞到C中的一維數組data后對應于data[j*M+i]?。?輸入數據是在函數調用之前已經在Matlab里申請了內存的，由于mex函數與Matlab共用同一個地址空間，因而在prhs[]里傳遞指針就可以達到參數傳遞的目的。但是，輸出參數卻需要在mex函數內申請到內存空間，才能將指針放在plhs[]中傳遞出去。由于返回指針類型必須是mxArray，所以Matlab專門提供了一個函數：mxCreateDoubleMatrix來實現內存的申請，函數原型如下：?
???mxArray?*mxCreateDoubleMatrix(int?m,?int?n,?mxComplexity?ComplexFlag)?
???m：待申請矩陣的行數?
???n：待申請矩陣的列數?
為矩陣申請內存后，得到的是mxArray類型的指針，就可以放在plhs[]里傳遞回去了。但是對這個新矩陣的處理，卻要在函數內完成，這時就需要用到前面介紹的mxGetPr。使用?mxGetPr獲得指向這個矩陣中數據區的指針（double類型）后，就可以對這個矩陣進行各種操作和運算了。下面的程序是在上面的show.c的基礎上稍作改變得到的，功能是將輸出處理后的元素：
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當然，Matlab里使用到的并不是只有double類型這一種矩陣，還有字符串類型、稀疏矩陣、結構類型矩陣等等，并提供了相應的處理函數。本文用到編制mex程序中最經常遇到的一些函數，其余的詳細情況清參考Apiref.pdf。? 另外，若是不是輸出元素，申請內存之后要記得釋放： mwSize?*subScript;?
subScript?=?(mwSize?*)mxCalloc(?numOfDim,?sizeof(?mwSize?)?);? mxFree(?subScript?);?
通過前面兩部分的介紹，大家對參數的輸入和輸出方法應該有了基本的了解。具備了這些知識，就能夠滿足一般的編程需要了。但這些程序還有些小的缺陷，以前面介紹的re由于前面的例程中沒有對輸入、輸出參數的數目及類型進行檢查，導致程序的容錯性很差，以下程序則容錯性較好
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在上面的異常處理中，使用了兩個新的函數：mexErrMsgTxt和mxIsDouble。MexErrMsgTxt在給出出錯提示的同時退出當前程序的運行。MxIsDouble則用于判斷mxArray中的數據是否double類型。當然Matlab還提供了許多用于判斷其他數據類型的函數，這里不加詳述。?
需要說明的是，Matlab提供的API中，函數前綴有mex-和mx-兩種。帶mx-前綴的大多是對mxArray數據進行操作的函數，如mxIsDouble,mxCreateDoubleMatrix等等。而帶mx前綴的則大多是與Matlab環境進行交互的函數，如mexPrintf，mxErrMsgTxt等等。了解了這一點，對在Apiref.pdf中查找所需的函數很有幫助。 另外，需要注意的是，當代碼的后綴名為.c的時候，需要一次性把變量聲明完，且放在代碼的最前面，后綴為.cpp不會出現這個問題。
常用的Mex函數一覽表
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 |
參考：
http://blog.sciencenet.cn/blog-620659-579885.html
http://blog.csdn.net/raodotcong/article/details/6295859
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