Time-limiting code

[EDIT: 20110523 17:40 CDT - clarify - WDR]

I need to give a program code in a m.file type. but I want that code be expired after a specific time. Can you help me?

[Jan]

Are you sure you need M-files? P-file cannot be modified or read in clear text. But a secure time limitation cannot be achieved by P-coding also.

Answer 1

[Sean de Wolski]

This topic was covered on CSSM:

http://www.mathworks.com/matlabcentral/newsreader/view_thread/260998

[Jan]

This thread concerns P-files. The OP asks for M-files - to my surprise.

[Sean de Wolski]

I'd guess the OP had never heard of a p-file.

Answer 2

[Jan]

M-files are very easy to edit. Therefore it is hard to imagine which level of protection you expect from such an expiration.

I assume the best expiration mechanism for an M-file is removing all comments, using minimalistic names for variables and subfunctions, interchange of variables by ASSIGNIN and EVALIN and using a flock of variables (G1, G2, G3, ...) instead of an array together with EVAL command to access them.

Then let the customer sign a contract, which includes the date of expiration. Without your support, such an ugly M-file is useless and the customer will delete it voluntarily.

There are some very good examples for this method in the FEX. Look for files, which have been rated with 1 star by John D'Errico. [EDITED: Tried to formulate the last sentence more clear.]

[Sean de Wolski]

Ha!

Clarification: Files that John rated with 1-star, not files of John's which have a 1-star rating from angry "homework script" authors.

[Oleg Komarov]

I would also suggest to modify your M-file to a one-liner and keep of course the normal version for yourself.

[Jan]

@John and all other hard-working FEX comment creators: Your comments improve the usability and quality of the complete FEX. Thanks!

[Walter Roberson]

I'm fond of variable names that include varying numbers of underscores, or which contain mixes of lower-case L and the digital 1 (which are virtually identical in some fonts.)

[Jan]

And I love using a Mex function to use fieldnames which contain spaces, line breaks, tabs and non-ASCII characters. Then even an inserted SAVE command does not create a usable dump of the variables.

[Walter Roberson]

Jan, when you create a field name that way, is it the single-byte characters or the double-byte characters? And if you have something like a struct(), does it use double-byte characters like the rest of MATLAB or does it "save space" by using single-byte characters?

[Jan]

The fieldnames are 8 bit UCHARs: CHAR(200) works as fieldname if created inside a Mex and accessed by "S.(char(200))", but CHAR(300) fails.

mxGetFieldNameByNumber replies a pointer to a \0 terminated C-string with a fixed distance of 64 byte - at least in all tests I've performed with Matlab 2009a, but this is not a proof.