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Write C Functions Callable from MATLAB (MEX Files)

Create C functions that can be called from MATLAB^® R2017b or earlier, using mxArray to access MATLAB variables and create arrays to return to MATLAB

You can call your own C programs from the MATLAB command line as if they were built-in functions. These programs are called MEX functions, and the function name is the MEX file name. MEX functions are not appropriate for all applications. MATLAB is a high-productivity environment whose specialty is eliminating time-consuming, low-level programming in compiled languages. In general, do your programming in MATLAB. Do not use MEX functions unless your application requires it.

To create a MEX function, write your programs using MATLAB APIs. The functions in these libraries facilitate the transfer of data between MEX functions and the workspace. To choose a MATLAB API, consider the following:

Create MEX functions using modern C++ features, as defined in the MATLAB Data API for C++. For more information, see Write C++ Functions Callable from MATLAB (MEX Files).
If your MEX functions must run in MATLAB R2017b or earlier, or if you prefer to work in the C language, then use functions in the C Matrix API and the C MEX API. These APIs use the MATLAB mxArray data structure. The functions and topics on this page are based on mxArray.

Note

Choose functions from either the C Matrix API or the MATLAB Data API; you cannot mix functions from these APIs.

Build your source file into an executable program using the mex function. You can also share the MEX file with other MATLAB users.

For information about writing S-functions, see your Simulink^® documentation.

To call a MEX function that someone else created, see Call MEX Functions.

If you have a C/C++ program and want to call MATLAB functions from the program, then use one of the engine APIs. For more information, see:

If you want to read and write MATLAB data from C programs, see Write C Programs to Read MAT-File Data.

Functions

`mex`	Build MEX function or engine application
`dbmex`	Enable MEX-file debugging on UNIX platforms

C MEX API

`mexFunction`	Entry point to C/C++ MEX function built with C Matrix API
`mexFunctionName`	Name of current MEX function
`mexAtExit`	Register function to call when MEX function clears or MATLAB terminates
`mexCallMATLAB`	Call MATLAB function, user-defined function, or MEX function
`mexCallMATLABWithTrap`	Call MATLAB function, user-defined function, or MEX file and capture error information
`mexEvalString`	Execute MATLAB command in caller workspace
`mexEvalStringWithTrap`	Execute MATLAB command in caller workspace and capture error information
`mexGetVariable`	Copy of variable from specified workspace
`mexGetVariablePtr`	Read-only pointer to variable from another workspace
`mexPutVariable`	Array from MEX function into specified workspace
`mexGet`	Value of specified graphics property
`mexSet`	Set value of specified graphics property
`mexPrintf`	ANSI C PRINTF-style output routine
`mexErrMsgIdAndTxt`	Display error message with identifier and return to MATLAB prompt
`mexWarnMsgIdAndTxt`	Warning message with identifier
`mexIsLocked`	Determine if MEX file is locked
`mexLock`	Prevent clearing MEX file from memory
`mexUnlock`	Allow clearing MEX file from memory
`mexMakeArrayPersistent`	Make array persist after MEX file completes
`mexMakeMemoryPersistent`	Make memory allocated by MATLAB persist after MEX function completes

Topics

Share MEX Files

Document Build Information in the MEX File
This example shows how to document the xtimesy MEX file built on a Windows^® platform using a Microsoft^® Visual C++^® compiler.

Troubleshooting

Build Errors

Getting Help When MEX Fails
To help diagnose compiler set up and build errors, call the mex function with verbose option -v.
Compiling MEX File Fails
What to do when compiling a MEX file fails.
Troubleshooting MEX API Incompatibilities
More information for warnings and error messages.
Troubleshooting and Limitations Compiling C/C++ MEX Files with MinGW-w64
Troubleshooting MEX files built with the MinGW-w64 compiler.
Symbol mexFunction Unresolved or Not Defined
Every MEX file needs a mexFunction.

Runtime Errors

Invalid MEX File Errors
What to do when you get an invalid MEX file error.
MEX Version Compatibility
For best results, run MEX files built with your MATLAB version.
MEX Platform Compatibility
If you get a binary MEX file from another source, be sure that the file was compiled for the same platform on which you want to run it.
MEX API Is Not Thread Safe
Do not call a single session of MATLAB on separate threads from a MEX file.
MEX File Segmentation Fault
What to do when a MEX file causes a segmentation violation or assertion.
MEX File Generates Incorrect Results
What to do when your MEX generates wrong answers.

Debugging

Debug on Microsoft Windows Platforms
Suggestions for debugging with Microsoft Visual Studio^®.
Debug on macOS Platforms
This example shows how to debug a MEX file on Mac Platforms.
Debug on Linux Platforms
This example shows how to debug a MEX file on Linux^® Platforms.

Write C Functions Callable from MATLAB (MEX Files)

Functions

C MEX API

Topics

Write C MEX Functions

Test Your Build Environment

C Matrix API Versions

Share MEX Files

Troubleshooting

Build Errors

Runtime Errors

Debugging

Related Information