mexme - write MEX files in no time

writes fully valid MEX .cpp files including mexFunction boilerplate based on numeric C/C++ snippet

967 Downloads

Updated Tue, 13 Nov 2012 15:00:03 +0000

View License

mexme automates the process of writing MEX files. You give mexme a snippet of C which just does numeric computations, as well a list of arguments, and it generates a valid MEX .cpp file. The generated code compiles in Linux (gcc) and in Windows (Visual Studio C++). New in version 1.1, it writes tedious input and output validation code for you. This way you can write a MEX file without manually coding calls to mx* API functions. It's inspired by SciPy's weave function.

Example: translate this piece of (non-vectorizable) .m code that applies a recursive filter into C:

function [y] = myrecursivefilter(x,alpha)
y = zeros(size(x));
y(1) = x(1)*alpha;
for ii = 2:length(x)
y(ii) = y(ii-1)*(1-alpha) + x(ii)*alpha;
end
end

Step 1: Write myrecursivefilter.csnip which does the same thing as the m file:

y[0] = x[0]*alpha;
for(mwSize i = 1; i < x_length; i++) {
y[i] = x[i]*alpha + y[i-1]*(1-alpha);
}

Step 2: Define arguments to your function (in Matlab):

inputargs = [InputNum('x'),...
InputNum('alpha',true,true,'double','alpha > 0 && alpha < 1)]; %scalar
%The last condition
outputarg = OutputNum('y','x_length,1');

Step 3: Generate a fully fledged .c file that can be compiled with mex:

cfile = mexme('myrecursivefilter.csnip',inputargs,outputarg)
writefile('myfilt.c',cfile);
mex myfilt.c
x = randn(1e6,1);
y = myfilt(x,.1);
plot([x,y])

cfile =

/*#include and #define not shown*/
#include "mexmetypecheck.c"

void mexFunction( int nlhs, mxArray *plhs[],
int nrhs, const mxArray *prhs[] )
{

/*Input output boilerplate*/
if(nlhs != 1 || nrhs != 2)
mexErrMsgTxt("Function must be called with 2 arguments and has 1 return values");

const mxArray *x_ptr = prhs[0];
const mwSize x_m = mxGetM(x_ptr);
const mwSize x_n = mxGetN(x_ptr);
const mwSize x_length = x_m == 1 ? x_n : x_m;
const mwSize x_numel = mxGetNumberOfElements(x_ptr);
const int x_ndims = mxGetNumberOfDimensions(x_ptr);
const mwSize *x_size = mxGetDimensions(x_ptr);
const double *x = (double *) mxGetData(x_ptr);
const mxArray *alpha_ptr = prhs[1];
if(mxGetNumberOfElements(alpha_ptr) != 1)
mexErrMsgTxt("Argument alpha (#2) must be scalar");
const double alpha = (double) mxGetScalar(alpha_ptr);
if(!(alpha > 0 && alpha < 1))
mexErrMsgTxt("Argument alpha (#2) did not pass test \"alpha > 0 && alpha < 1\"");

mwSize y_dims[] = {x_length,1};
plhs[0] = mxCreateNumericArray(2,y_dims,mxDOUBLE_CLASS,mxREAL);
mxArray **y_ptr = &plhs[0];
double *y = (double *) mxGetData(*y_ptr);

/*Actual function*/
#include "myfilt.csnip"

}

For every argument that you define, mexme generates extra "magic" variables. For example, if the variable is x, then in C:

x is the data
x_m is the size of the first dimension
x_n is the size of the second dimension
x_length is the length of a vector
x_numel is the number of elements in an array
x_ndims is the numer of dimensions
x_size is equivalent to the Matlab code size(x)
x_ptr is a reference to the mxArray that contains the x data

And if x is complex, x_r and x_i are the real and imaginary components of the data.

mexme currently does not support sparse data or non-numeric types but it does support full numeric arrays of any type (int8, single, double, etc.).

Cite As

Patrick Mineault (2023). mexme - write MEX files in no time (https://www.mathworks.com/matlabcentral/fileexchange/31257-mexme-write-mex-files-in-no-time), MATLAB Central File Exchange. Retrieved .

MATLAB Release Compatibility
Created with R2008b
Compatible with any release
Platform Compatibility
Windows macOS Linux
Acknowledgements

Inspired by: verbatim: Get the text of a block comment.

Inspired: Fast B-spline class

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!
Version Published Release Notes
1.8.0.0

Implemented Jan Simon's suggestions, including compatibility with Visual Studio

1.7.0.0

Added compatibility with Visual Studio and implemented Jan Simon's suggestions

1.4.0.0

Added input/output validation code generation

1.3.0.0

Added TestMexMe.m in zip file

1.2.0.0

Added reference to verbatim

1.0.0.0