gcc problem: c++ tmplates

[stinos]

Hi All,

I'm currently using gcc 4.20 and I'm running into problems with templates. Afaik the latest gcc versions are quit strict in meeting the standard, so I'm probably doing something wrong, but I don't see what.. (reading the standard didn't help, the lingo is quite weird ;-)

here's a simplified test case:

template< class T >
struct tTest
{
  template< class T2 >
  static T2 func()( const T& ac_tType )
  {
      //actual code does stuff to convert T->T2 here
    return T2();
  }
};
 
template< class T >
struct tUsesTest
{
  typedef tTest< T > mt_Test;
 
  void func()
  {
    T test;
    int nConverted = mt_Test::func( test );
  }
};
 
 
int main( argc, argv )
{
  tUsesTest< unsigned > test;
  test.func();
  return 0;
}

template< class T >
struct tTest
{
  template< class T2 >
  static T2 func()( const T& ac_tType )
  {
      //actual code does stuff to convert T->T2 here
    return T2();
  }
};

template< class T >
struct tUsesTest
{
  typedef tTest< T > mt_Test;

  void func()
  {
    T test;
    int nConverted = mt_Test::func( test );
  }
};


int main( argc, argv )
{
  tUsesTest< unsigned > test;
  test.func();
  return 0;
}

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this gives:
20: error: no matching function for call to 'tTest<unsigned int>::func(unsigned int&)'

replacing line 20 with

int nConverted = mt_test::func< int >( test );

int nConverted = mt_test::func< int >( test );

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yields:
20: error: expected primary-expression before 'int'

Can anyone explain in understandable language why this fails, and how to code this correctly?
Thanks in advance!

[marcel]

template< class T >
struct tTest
{
  template< class T2 >
  static T2 func( const T& ac_tType )
  {
      //actual code does stuff to convert T->T2 here
    return T2();
  }
};
 
template< class T >
struct tUsesTest
{
  typedef tTest< T > mt_Test;
 
  void func()
  {
    T test;
    int nConverted = mt_Test::func<unsigned int>( test );
  }
};
 
int main(int argc, char* argv[])
{
  tUsesTest< int > test;
  test.func();
    return 0;
}

template< class T >
struct tTest
{
  template< class T2 >
  static T2 func( const T& ac_tType )
  {
      //actual code does stuff to convert T->T2 here
    return T2();
  }
};
 
template< class T >
struct tUsesTest
{
  typedef tTest< T > mt_Test;
 
  void func()
  {
    T test;
    int nConverted = mt_Test::func<unsigned int>( test );
  }
};

int main(int argc, char* argv[])
{
  tUsesTest< int > test;
  test.func();
    return 0;
}

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You had a couple of errors back there. For example you did not specify the T2 type for func in tUsesTest. So the compiler could not deduce the type out of thin air
.
And in tTest, func had a weird syntax. It did resembled a bit with pointer to function syntax, but it wasn't correct.

Try the code I posted. Should work with gcc too.

[stinos]

You had a couple of errors back there. For example you did not specify the T2 type for func in tUsesTest. So the compiler could not deduce the type out of thin air
.
And in tTest, func had a weird syntax. It did resembled a bit with pointer to function syntax, but it wasn't correct.

ok sorry for the typos..

Try the code I posted. Should work with gcc too.

well that's the same as what I did here

int nConverted = mt_test::func< int >( test );

int nConverted = mt_test::func< int >( test );

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and that doesn't work with gcc (tried both 4.0.1 and 4.2).. it does with msvc8.0, but I'm not sure which of the two is correct here.

[marcel]

Try this:

int nConverted = mt_Test::template func<unsigned int>( test );

int nConverted = mt_Test::template func<unsigned int>( test );

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You got your error because func is dependent on the template type, which is resolved at instantiation time( your function is static.

BTW, you can use ->template when accessing template functions for pointers and .template for objects.

These cool things have been introduced in the standard by necessity( my opinion ).

regards

[stinos]

well thanks alot! that does indeed do the trick!