Unnecessary copying of variables in generated code

Hi, I am trying to call a function that has an argument both as input and output (for example: varA=foo(varA)). In the generated C-code, the variable varA is first copied to some temporary variable, then varA (the original, not the temporary) is passed (as a pointer) to the function and in the end the temporary variable is copied back to varA.

Is there any way to prevent this from happening?

Thank you.

[Arnab De]

Can you please tell us which version of MATLAB you are using?

[Mike Hosea]

Another question: Is the function defined in the a = foo(a) form, or is that just what the call site looks like?