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comp.lang.c++

template-based test function for unary operators?

Jan Wagner

10/3/2008 6:26:00 PM

Somewhat a C++ beginner, I'm trying to make a general test function
that could test unary operators (or methods) of an object of any class.

Arguments are a member-pointer to the function, a single input
argument of some type for that function, and the expected result of
some type. Then it tests if the result is as expected, and does some
logging of the results (pass, fail) etc.

Well, the template "mess" does not quite work out.

Below is the code. After that, the error messages.

--------------------------------------------------------

class A {
int f (int c) { return c; }
int f (const char c) { return c; }
A& operator+= (A const& a) { return *this; }
};

template <class rettype, class argtype, class btype>
bool unary_op_test(rettype (*func)(argtype),
btype self, argtype arg, rettype expect)
{
rettype rv = self.func(arg);
bool result = (rv == expect);
return result;
}

int main ()
{
A aa;
int (A::*p1)(int) = &A::f;
A& (A::*p2)(A const&) = &A::operator+=;
unary_op_test<int,int,A&>(p1, aa, 12, 12);
unary_op_test<A&,A&,A&>(p2, aa, aa, aa);
unary_op_test<A&,const A&,A&>(p2, aa, aa, aa);
}

--------------------------------------------------------

$ g++ -Wall -pedantic test.cc
test.cc: In function 'int main()':
test.cc:21: error: no matching function for call to
'unary_op_test(int (A::*&)(int), A&, int, int)'
test.cc:22: error: no matching function for call to
'unary_op_test(A& (A::*&)(const A&), A&, A&, A&)'
test.cc:23: error: no matching function for call to
'unary_op_test(A& (A::*&)(const A&), A&, A&, A&)'

--------------------------------------------------------

How come "A& (A::*&)(const A&)" does not map to "rettype
(*func)(argtype)"<templated> i.e. to "A&(*func)(const A&)"?

Sure some beginner mistake somewhere... :)

Any ideas?

- Jan
3 Answers

Victor Bazarov

10/3/2008 6:38:00 PM

0

JanW wrote:
> Somewhat a C++ beginner, I'm trying to make a general test function that
> could test unary operators (or methods) of an object of any class.
>
> Arguments are a member-pointer to the function, a single input argument
> of some type for that function, and the expected result of some type.
> Then it tests if the result is as expected, and does some logging of the
> results (pass, fail) etc.
>
> Well, the template "mess" does not quite work out.
>
> Below is the code. After that, the error messages.
>
> --------------------------------------------------------
>
> class A {
> int f (int c) { return c; }
> int f (const char c) { return c; }
> A& operator+= (A const& a) { return *this; }
> };
>
> template <class rettype, class argtype, class btype>
> bool unary_op_test(rettype (*func)(argtype),
> btype self, argtype arg, rettype expect)
> {
> rettype rv = self.func(arg);
> bool result = (rv == expect);
> return result;
> }
>
> int main ()
> {
> A aa;
> int (A::*p1)(int) = &A::f;
> A& (A::*p2)(A const&) = &A::operator+=;
> unary_op_test<int,int,A&>(p1, aa, 12, 12);
> unary_op_test<A&,A&,A&>(p2, aa, aa, aa);
> unary_op_test<A&,const A&,A&>(p2, aa, aa, aa);
> }
>
> --------------------------------------------------------
>
> $ g++ -Wall -pedantic test.cc
> test.cc: In function 'int main()':
> test.cc:21: error: no matching function for call to 'unary_op_test(int
> (A::*&)(int), A&, int, int)'
> test.cc:22: error: no matching function for call to 'unary_op_test(A&
> (A::*&)(const A&), A&, A&, A&)'
> test.cc:23: error: no matching function for call to 'unary_op_test(A&
> (A::*&)(const A&), A&, A&, A&)'
>
> --------------------------------------------------------
>
> How come "A& (A::*&)(const A&)" does not map to "rettype
> (*func)(argtype)"<templated> i.e. to "A&(*func)(const A&)"?
>
> Sure some beginner mistake somewhere... :)
>
> Any ideas?

Only one idea so far: the type "a pointer to a [non-static] member
function of class T" is not convertible to "a pointer to function".

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Jan Wagner

10/3/2008 6:50:00 PM

0

Victor Bazarov wrote:
> JanW wrote:
<snip>
> Only one idea so far: the type "a pointer to a [non-static] member
> function of class T" is not convertible to "a pointer to function".

Oops, true. That was quick, thanks :-)

After the first attempts it has now started working. As a first
version, just rewriting unary_op_test() to like below (and defining
A::operator== in class A) removes the complaints:

template <class rettype, class argtype, class btype>
bool unary_op_test(rettype (btype::* func)(argtype), btype& self,
argtype arg, rettype expect)
{
rettype rv = (self.*func)(arg);
bool result = (rv == expect);
return result;
}

And then call the tests like below:

unary_op_test<int,int,A>(p1, aa, 12, 12);
unary_op_test<A&,const A&,A>(p2, aa, aa, aa);
unary_op_test(p1, aa, 12, 12);

Thanks!

- Jan

Gennaro Prota

10/3/2008 6:58:00 PM

0

JanW wrote:
> Well, the template "mess" does not quite work out.
>
> Below is the code. After that, the error messages.
>
> --------------------------------------------------------
>
> class A {
> int f (int c) { return c; }
> int f (const char c) { return c; }
> A& operator+= (A const& a) { return *this; }
> };
>
> template <class rettype, class argtype, class btype>
> bool unary_op_test(rettype (*func)(argtype),
> btype self, argtype arg, rettype expect)
> {
> rettype rv = self.func(arg);
> bool result = (rv == expect);
> return result;
> }
>
> int main ()
> {
> A aa;
> int (A::*p1)(int) = &A::f;
> A& (A::*p2)(A const&) = &A::operator+=;
> unary_op_test<int,int,A&>(p1, aa, 12, 12);
> unary_op_test<A&,A&,A&>(p2, aa, aa, aa);
> unary_op_test<A&,const A&,A&>(p2, aa, aa, aa);
> }

Pointers to member functions are not pointers to functions, and there's
no implicit conversion. There are other issues in your code, but this is
the main one. Here's a rough function template accepting a pointer to
member function:

template< typename Ret, typename C, typename Arg>
void f( Ret ( C::*pmf )( Arg ),
C & c,
Arg a )
{
( c.*pmf )( a ) ;
}

usable as follows:

A instance = {} ;
int ( A::*p1 )( int ) = &A::f;
f( p1, instance, 12 ) ;

--
Gennaro Prota | name.surname yahoo.com
Breeze C++ (preview): <https://sourceforge.net/projects/b...
Do you need expertise in C++? I'm available.