Why is this invalid as a function prototype? (c++)

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cyclone3d

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template<class type, class type2, class type3>
void sieve(CPrime<type, type2, type3> *cPrime);

Any time I have this as a function prototype, VS2010 gives me an error that this is an "illegal use of type void" and stops my build?

When I just use it for the actual function definition, it compiles properly.
 
Are you aware that template classes and functions are not separated into header and implementation? The implementation must be with the header, because the information on how to generate instances of the function for types T must be known at compile time.
 
Cyrilix said:
Are you aware that template classes and functions are not separated into header and implementation? The implementation must be with the header, because the information on how to generate instances of the function for types T must be known at compile time.
Click to expand...

I'm not using a header file for this. The prototype is near the top of my main source file and the implementation is in my main source file.

All of the other templated function prototypes work fine. The only difference is that none of the other functions I have prototyped have anything passed into them.
 
You might need a "typename" before CPrime in the parameter list...

void sieve(typename CPrime<type, type2, type3> *cPrime);

I'm not 100% on templates but we just had an assignment and I remember that was required when we were returning templated classes, so it might be required for the parameters as well.
 
I don't think anyone can help you without seeing the declaration of CPrime.
 
mikeblas said:
I don't think anyone can help you without seeing the declaration of CPrime.
Click to expand...

Guess I should have incuded it... In any case, here is the declaration of CPrime

template<class type, class type2, class type3>
class CPrime : public ting::Thread
 
Arainach said:
We'd need to see more of the code to know for sure.
Click to expand...

O.k., here is the complete CPrime class:

Code: 
template<class type, class type2, class type3>
class CPrime : public ting::Thread
{
   public:
     int iNum;
     my_uint32 array_id;
   
    void Run() //override
    {
       if(choice == 1)
       {
          if (iNum == 0)
          { 
             first_prime_sieve<type>();
             array_id = cpu_cores;
          }
          else 
          {
             array_id = iNum;
          }
          while(array_id < total_work_units)
          {
             prime_sieve<type, type2>(array_id);
             array_id += cpu_cores;
          }
       }
       else
          if(choice == 2)
          {
             array_id = iNum;
             while(array_id < total_work_units)
         {
         prime_sieve_range<type, type3>(array_id);
         array_id += cpu_cores;
       }
    }
 };
};

And here is the sieve function:

Code: 
template<class type, class type2, class type3>
void sieve(CPrime<type, type2, type3> *cPrime)
{
   my_uint32 i;

   for(i=0; i<cpu_cores; i++)
   {   
      cPrime[i].iNum = i;
		
      again:
      try
      {
         cPrime[i].Start();
      }
      catch (exception& e)
      {
         cout << e.what() << endl;
         cout << "Trying thread: " << i  << " again." << endl;
         goto again;
       }
   }

// Wait for all threads to end before continuing 
   for (i = 0; i<cpu_cores; i++)
   {
      cPrime[i].Join();
   }

   delete[] cPrime;

   return;
}
 
Last edited:
For reference, I just wrote this, that compiles and runs fine in VS2010:
Code: 
#include <iostream>
using namespace std;

template<class A, class B, class C>
class foo
{
public:
    A item1;
    B item2;
    C item3;

    foo(A a, B b, C c)
        : item1(a), item2(b), item3(c) {};
};

template <class D, class E, class F>
void sieve(foo<D,E,F> *cPrime)
{
    if (!cPrime)
    {
        cout << "Null Pointers are bad, mmkay?" << endl;
    }
    else
    {
        cout    << "item1: " << cPrime->item1 << endl
                << "item2: " << cPrime->item2 << endl
                << "item3: " << cPrime->item3 << endl;
    }
}

int main()
{
    foo<int, float, bool> myFoo(42, 3.14159f, false);

    sieve<int, float, bool>(&myFoo);

    return 0;
}
If I move the implementation of sieve to the bottom of the file and leave a declaration at the top of the file, it still works fine. My guess is you have another error in your file somewhere (missed semicolon after a class or struct definition?) that is causing the error.
 
hrmmm...

Here it is surrounded by other function declarations.

Code: 
template<class type, class type2>
void prime_sieve_range(my_uint32 work_unit_id);

template<class type, class type2, class type3>
void sieve(CPrime<type, type2, type3> *cPrime);

void prime_number_test(my_uint32 work_unit_id);

It only gives me that stupid error when the declaration for sieve is there.... :mad:
 
Last edited:
Yep, no matter where I put that function declaration in my function declarations it gives me that error.

As soon as I comment out that function declaration it compiles fine.

I even tried moving some variables and a few defines down to where the rest of them were and it made no difference.

I have looked through my code line by line and cannot find anything wrong,

It compiles and runs great without that function declaration there..... so weird.
 
Figured it out... was a lame mistake on my part. I was declaring the function before the class. As soon as I put the function declaration after the class the error went away.
 
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