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Posted: **07 Mar 2011, 18:36**

Hello,

I'm working on an extension and want to pass an integer argument by reference. I tried the following perl-glue code:

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UserFunction4perl("# Tests a given //matrix// for k-modularity, without certificates. It also computes k."
      "# @param Matrix<int> matrix"
      "# @param int& k"
      "# @return Bool",
      &is_k_modular_compute,"is_k_modular(Matrix<Integer>, $&)");

Neither "$" nor "$&" or anything else I tried has worked. Can you help me here?

The function signature is as follows:

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bool is_k_modular_compute(const Matrix <Integer>& matrix, int& ko)

Thank you!
Matthias Walter

Posted: **07 Mar 2011, 18:59**

You can't pass perl primitive types to C++ code by reference, they are not stored in C++ representation. If you want to return several values from a function, please use std::pair or perl::ListReturn.

Alternatively, your function would look more adhering to perl habits if it would return k if the matrix is k-modular and undef otherwise. Again, perl::ListReturn will facilitate this. Just return an empty list in negative case.

Posted: **08 Mar 2011, 14:40**

Thank you for the helpful reply! I managed to get it working with perl::ListReturn. The only drawback is that there was another version of the routine which did not compute k (to save running time) which I removed now. But I think it's okay as the running time gain is not a lot.

Posted: **08 Mar 2011, 15:25**

Well, you can still have two functions, just give them different names...

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