What is a mex file?

What is a MEX file?

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More information

Compiling

Method 1

Method 2 (Matlab 6.0 and later)

1. 
   From the development environment, create a new Win32 Dynamic-Link Library project (empty). When selecting a project name, I usually end it in “_mex” to differentiate it from a stand alone .exe version.
   

2. 
   Once the project MyFunction_mex is created, modify the project settings (shortcut is Alt-F7).
   

Table 1, Changes to project settings

3. 
   Add C source files to the project, one of which must contain a function called mexFunction. (See below.) That file (and maybe others) should contain the directive
   

Method 2 (Matlab 5.3 and earlier)

1. 
   Projects can be created which have dependencies on other projects. A separate project is created to build the file “meximports.lib”, which needs to be done only once, regardless of the number of mex-file projects in the workspace.
   

2. 
   Linker options can be explicitly added to the link step to define exported functions, eliminating the need for the “MyFuntion_mex.DEF” file.
   

Here is an overview for creating a mex-file using this method.

1. 
   From the development environment, create a new Win32 Static Library project (empty). Name the project “meximports”. You may opt to “Add to Current Workspace” if you are converting an existing project.
   

2. 
   Add a file to the project (by right-clicking on the project name from “File View”), “e:\matlab\extern\include\matlab.def”. (The path may vary depending on where Matlab was installed.)
   

3. 
   Modify the settings for the file “matlab.def” as follows:
   

Next, create a project to build the mex-file, which will have a dependency on the above project:

1. 
   From the development environment, create a new Win32 Dynamic-Link Library project (empty). Name the project appropriate for your new MEX-file. When creating the project, select the “Add to Current Workspace” radio button, is the project is placed in the same workspace as the meximports.dll project.
   

2. 
   Once the project MyFunction_mex is created, modify the project settings (shortcut is Alt-F7).
   

Table 3, Changes to project settings

3. 
   From the menu bar, select Project->Dependencies. Make sure the “Select project to modify” field is set to the new mex-file project. In the “Dependent on the following projects” area, mark the checkbox labeled “meximports”.
   

When the new mex-file project is built, is should first create the meximports.lib file, and then continue building the mex-file project. Note that many mex-file projects in the same workspace can have a dependency on the meximports project.

Method 3

4. 
   From the development environment, create a new Win32 Dynamic-Link Library project (empty). When selecting a project name, I usually end it in “_mex” to differentiate it from a stand alone .exe version.
   

5. 
   Once the project MyFunction_mex is created, modify the project settings (shortcut is Alt-F7).
   

Table 4, Changes to project settings

6. 
   Add a file to the project called MyFunction_mex.def. Type the following contents into the file:
   

EXPORTS mexFunction

7. 
   Add C source files to the project, one of which must contain a function called mexFunction. (See below.) That file (and maybe others) should contain the directive
   

Debugging

where msdev is the Microsoft Development Studio, the C development environment, also the function being debugged must be executed once before breakpoints can be set in the C code.

Caveats/suggestions

LINK : fatal error LNK1168: cannot open MyFunction.dll for writing

It’s because Matlab is still running after having invoked the DLL. To fix, simple type at the Matlab command prompt clear functions, or exit Matlab altogether.
Another important note: McAffee virus scan 4.0.2 and above can cause the pre-link build step to hang. To resolve this, either temporarily disable the virus scanner, or under the McAffee System Scan properties, Select “Program Files Only” under the Detection tab. See http://support.microsoft.com/support/kb/articles/Q250/6/70.ASP
Any files opened within a mex file should also be closed; else a new file will be opened each time the function is called, which could result in an “out of files” error.
Static variables may be used with in the code, which persist between function calls. However, clear functions Matlab command will cause the static variables to disappear.
printf() statements may be used freely within the C code.
Do not use malloc() or free() functions. Use mxCalloc(), mxFree(), or related mex function instead.

Sample Program

* file: MyFunction.c - Sample MEX source file. *

* Finds the unique data values in an array. *

***************************************************************/

#include
#include "mex.h"
/***************************************************************

* function: UniqueValues() - Find all the unique values within *

* a data set. *

* INPUTS: *

* pDataIn - Pointer to double floating point array of data *

* to be processed. *

* N - The number of double values in pDatain. *

* pDataUnique - Pointer to where unique values are placed. *

* RETURNS: *

* Count of the number of unique values. *

* NOTES: *

***************************************************************/

int UniqueValues(double *pDataIn, int N, double *pDataUnique)

{

int Count = 0; /* Count of number of unique values */

int j; /* Iteration counter for searching list of unique data */

double Tolerance; /* How close values must be to be non-unique */

int Unique_Flag; /* Set until it's determined a value is a duplicate */

/* a parameter passed in from Matlab */

for (i=0; i

{

Unique_Flag = 1;