This is a collection of notes made when using the Matlab compiler under Matlab 6 (2003) and Matlab 7 (2006) which may be of use to Matlab compiler users.
Matlab 6 notes
The Matlab compiler is a useful utility which enables you to turn your Matlab code into C/C++ and compile it. The compiler doesn’t really compile your code at all… it translates your Matlab code into C line for line. The C/C++ code produced is unreadable do don’t count on being able to modify it or even understand it! Mex files can be included, watch out for relative paths names though, some documentation on this on Matlab homepage.
Don’t use the remez filter generation command in Matlab as the compiler can’t compile it. There is a fix but it is complicated, see this.
Other functions such as eval and keyboard are unsupported by the compiler. The save command only supports .mat format, not ascii format.
Make sure you test the executable you’ve produced on other machines especially if you intend to deploy the code for other users! I have found that code would work fine on the machine it was compiled on but produce run-time errors on other machines due to missing dlls & incorrect relative paths.
When you supply a command line argument to the executable when running from the DOS command line, it is passed to the internal code as a string even if it is a number. You need to use a command such as
to convert these into numbers. Of course now if you run this code under Matlab, it doesn’t work… I used a compile variable to execute different parts of code depending on whether we were running under Matlab or in a compiled version of the code:
If you run the compiler command (mcc) from a DOS prompt or Perl script etc, you need to make sure you’ve got the Matlab path saved as a Windows variable or else the compiler can’t find any libraries such as the wavelet toolbox. Use the mccsavepath utility to do this.
When giving executable models to other users, you also need to supply the Matlab run-time libraries. These are supplied with matlab compiler, but can also be downloaded from the mathworks homepage.
Matlab 7 notes
For Matlab 7, the compiler has been revised extensively. It now encrypts your code along with the built-in Matlab functions you’ve used. It presumably decrypts these at run-time.
A few more issues:
You need to be VERY CAREFUL here as the compiler makes no effort to change either directory structures or filenames. If you are using some bespoke algorithm/ method in your system which you regard as proprietary and you name your filename after this, e.g. 16TapRLS.m then the one who uses your deployed application is going to see it!
Compiler doesn’t like working over networked file stores, sometimes it fails for strange reasons.
C files with a mex interface used to be called .dll files are now called .mexw32. Matlab 7 only uses .mexw32 file and will helpfully rename your .dll files to .dll.old when you recompile your .c files rendering them useless under Matlab 6.
Some things have been improved since version 6:
Introduction of isdeployed function to indicate if you are running in Matlab or compiled environment. The following code can be used to handle this whilst retaining backwards run compatability to Matlab 6.
Compiled code still can’t handle numerical inputs from command line.
Compiled code can now load .mat files in same way as native code i.e.
The mex function has the following format:
The Matlab mex documentation gives a full explanation of how to access arguments and return values. The mex function allows multiple values to be returned from a C-function. However, the function arguments are passed by address and can therefore be changed within the C-code; these changes are reflected in the matlab environment.
An example shows a mex function called product, written in a file called product.c as:
The mex call in matlab could be:
The value of c will be 200, b will be 20 but a will now be 200 also. The example seems obvious but can be easily overlooked when dealing with more complex functions.
Other notes:
- If the mex function creates static variables, these are created dynamically the first time the function is called and remain persistent for future calls.
- The matlab clear function will clear only matlab variables from the workspace; clear all will properly clear any variables, such as static variables, allocated by the mex function.
- The mex compiler error LINK : fatal error LNK1168: cannot open your_mexfunction.dll for writing is caused by static variables persisting after your_mexfunction has been called in the Matlab environment. The clear all command will remedy this.
- The compiled mex function has a .dll extension under Matlab 6 (Matlab 7 uses .mexw32). If the function has been called, the DLL file cannot be deleted until clear your_mexfunction or clear all is used.
- Creating a mex build script is difficult since matlab string variables cannot be referenced within the mex command. However, the mex command can be simplified by using the triple dot ‘…’ directive to separate the command. Particularly useful for very large build commands, e.g.
