MATLAB: Does the Simulink model, which used to work fine in Simulink 4.0 (R12), return an error message “One or more output arguments not assigned during call” when executed in Simulink 6.0 (R14) and later versions

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When I run my model containing a S-Function in Simulink 6.0 (R14) and later release, I receive the following error:
 One or more output arguments not assigned during call
The S-Function is calling a user-defined MATLAB file.

Best Answer

This is expected behavior. This error obtained is due to the change in behavior in the way that output arguments are assigned inside a M-function call.
In the newer release, you need to assign an output inside M-function, if one is requested, or throw an error if no output is available. The older release implicitly assigned [] to the output.
To work around this issue, you can return an empty value to the function output argument, as in the following example:
function y = foo(a)
disp('hello world ');
y=[];
Here is some additional information about the change in functionality:
There is a minor change from MATLAB 6.0 (R12) to MATLAB 7.0 (R14) and later in the way output arguments are assigned during a function call.
Consider the following example:
function y = foo(a)
disp('hello world');
If you execute this function in MATLAB 7.0.4 (R14SP2), you see the following result:
 >> x = foo(2)
 hello world 
 ??? Output argument "y" (and maybe others) not assigned during call to "Y:\1-1UZXOV\foo.m (foo)".
 Error in ==> foo at 2
 disp('hello world ');
If you execute the same function in MATLAB 6.0 (R12), you see the following result:
 >> x = foo(2)
 hello world 
 Warning: One or more output arguments not assigned during call to 'foo'.
 >>
Behavior that resulted in a warning in MATLAB 6.0 (R12) results in an error in MATLAB 7.0 (R14) and later versions.
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