Setting function return type

I want my function to return the type mpz_t, but I'm not sure how?

I've tried:
mpz_t MyFunction(mpz_t A, mpz_t B){}

But it didn't work, here is my code so far, I have bolded the parts of the code which are causing errors and added the errors in the comments:

Code:

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#include <iostream>
#include <mpir.h>

using namespace std;

???? A(mpz_t m, mpz_t n){
        mpz_t mmo; //used to store the value of m, minus one
        mpz_t nmo; //used to store the value of n, minus one
        mpz_t one; //used to store the value 1
        mpz_init(mmo);
        mpz_init(nmo);
        mpz_init(one);
        mpz_set_ui(one, 1);

        if(mpz_cmp_ui(m, 0) == 0){
                mpz_add_ui(n, n, 1);
                return n; //error: return value type does not match the function type
        }

        if(mpz_cmp_ui(m, 0) > 0 && mpz_cmp_ui(n, 0) == 0){
                mpz_sub_ui(mmo, m, 1);
                return A(mmo, one);
        }

        if(mpz_cmp_ui(m, 0) > 0 && mpz_cmp_ui(n, 0) > 0){
                mpz_sub_ui(mmo, m, 1);
                mpz_sub_ui(nmo, n, 1);
                return A(mmo, A(m, nmo));
        }
}

int main(){
        mpz_t param1;
        mpz_init(param1);
        mpz_t param2;
        mpz_init(param2);

        mpz_set_ui(param1, 4);
        mpz_set_ui(param2, 2);

        mpz_out_str(stdout, 10, A(param1, param2));
        return 0;
}

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Is there a way around this?

Thank you :)

There's a disconnect between what you say you tried and what you implemented. Your implementation shows a void function trying to return something.

Sorry, I was trying something else before I posted this and forgot to change it

What is A?

Quote:

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Originally Posted by SamstaUK

I want my function to return the type mpz_t, but I'm not sure how?

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Why are you returning a variable name?

Code:

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mpz_t MyFunction(mpz_t A, mpz_t B){}
//...
return A(mmo, one);  // ?

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The A is the name of the variable, not the type. Aren't you supposed to do something like this?

Code:

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return mpz_t(mmo, one);

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?
Also, what is mpz_t? If it's a class or struct, you should be passing them by reference or const reference, not by value, unless there is a compelling and logical reason to be passing them by value.

Code:

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mpz_t MyFunction(mpz_t& A, mpz_t& B)

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Regards,

Paul McKenzie

Quote:

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Originally Posted by SamstaUK

I want my function to return the type mpz_t, but I'm not sure how?

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Read the GMP manual on parameter conventions:

Quote:

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When a function is going to return a GMP result, it should designate a parameter that it sets, like the library functions do. More than one value can be returned by having more than one output parameter, again like the library functions. A return of an mpz_t etc doesn't return the object, only a pointer, and this is almost certainly not what's wanted.

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Also, note that what you mpz_init, you must mpz_clear, similiar to the rule that what you malloc, you must free. Alternatively, you can use the C++ wrapper and let RAII do the work for you.

Quote:

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Originally Posted by Paul McKenzie

Also, what is mpz_t?

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An opaque pointer type.