If you have an older version (2017a or newer) or a different OS you can still work with MEX files, but you will need to manually configure MinGW
MinGW-w64 Add-On If you have issues, try launching MATLAB with administrator privileges.
Simply click "Install" in the upper right of the download page and the compiler will automatically configure itself. This may take a few minutes.
MEX files can be created from C,C++, or FORTRAN files. C++ is generally recommended over C, but to keep our example simple we will use C.
Here is our example C file
#include "mex.h"
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
if(nrhs==0) {
mexPrintf("Hello, World!\n");
}
if(nrhs==1) {
if (!mxIsChar(prhs[0])) {
mexErrMsgIdAndTxt("helloworld:notString", "Input must be a string.");
}
// Get the input string
char *inputString = mxArrayToString(prhs[0]);
if (inputString == nullptr) {
mexErrMsgIdAndTxt("helloworld:conversionFailed", "String conversion failed.");
}
// Print "Hello, <name>"
mexPrintf("Hello, %s!\n", inputString);
}
}
With the C API, we simply need a function called "mexFunction". The inputs for the function are
nlhs: The number of returned objects by our MATLAB function
plhs: The pointers to the returned objects of the MATLAB function
nrhs: The number of inputs being passed to the function in MATLAB
prhs: The pointers to the inputs we pass the MATLAB function
Here's what the code does:
First, if no inputs are given, say "Hello World!"
if(nrhs==0) {
mexPrintf("Hello, World!\n");
}
If an input is provided, make sure it has the char type and not a null pointer. Then, greet our new friend!
if(nrhs==1) {
if (!mxIsChar(prhs[0])) {
mexErrMsgIdAndTxt("helloworld:notString", "Input must be a string.");
}
// Get the input string
char *inputString = mxArrayToString(prhs[0]);
if (inputString == nullptr) {
mexErrMsgIdAndTxt("helloworld:conversionFailed", "String conversion failed.");
}
// Print "Hello, <name>"
mexPrintf("Hello, %s!\n", inputString);
}
Notice we can print directly to the MATLAB console from our MEX file as well as throw errors inside MATLAB. If we want to return a value, the method is similar to how we handled the inputs.
If you want to include outputs, the process is similar to the way we handled inputs. First, you would create the object to return and then assign the variable plhs[i] that object as a value. The links above have several useful examples covering how to handle inputs, different data types, and many other common situations.
To compile hello.cpp into a MEX file, we will need to use the mex command. For our simple example, if hello.cpp is in your working directory or on your MATLAB path, you can use type the following into your MATLAB terminal:
mex hello.cpp
This will compile hello.cpp and create a file called "hello.mexw64".
Our example is pretty simple. For a realistic project, you might need to use compiler flags. For example, if you type
mex hello.cpp -output "greeting"
then the MEX file will instead be called "greeting.mexw64". See the mex documentation linked about for the full list of supported compiler options.
From here, as long as the compiled file is in your current working directory or the MATLAB path, you can use it just like any other MATLAB command. Let's try out a few different cases:
hello()
hello('Alice')
hello(0)