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Static Member Function Template Specialization

P: n/a
Hello everyone, thanks in advance for your help. I'm new to C++
templates and have run into some issues using member function
templates. I have a shared library containing templates that I'm
trying to use from an executable, compile using gcc 4.1.2. Everything
works fine until I try specializing one of the static member function
templates in a non-template class. I have a feeling I'm messing up
something obvious so before I post a bunch of code does the following
look correct? Thanks.

--- Shared Library (Arrays.h) ---

namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
protected:
Arrays() {};
};

template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
printf("Calling generic function.\n");
return 1;
}

template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
printf("Calling char specialization.\n");
return 0;
}
}

Oct 14 '07 #1
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13 Replies


P: n/a
On 2007-10-14 18:38, mike b wrote:
Hello everyone, thanks in advance for your help. I'm new to C++
templates and have run into some issues using member function
templates. I have a shared library containing templates that I'm
trying to use from an executable, compile using gcc 4.1.2. Everything
works fine until I try specializing one of the static member function
templates in a non-template class. I have a feeling I'm messing up
something obvious so before I post a bunch of code does the following
look correct? Thanks.

--- Shared Library (Arrays.h) ---

namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
protected:
Arrays() {};
};

template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
printf("Calling generic function.\n");
return 1;
}

template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
printf("Calling char specialization.\n");
return 0;
}
}
I can see nothing wrong with it (except using printf and not including
<stdio.h>). What error messages are you getting and how are you trying
to use the function?

--
Erik Wikström
Oct 14 '07 #2

P: n/a
On Oct 14, 12:38 pm, mike b <michaeljber...@gmail.comwrote:
Hello everyone, thanks in advance for your help. I'm new to C++
templates and have run into some issues using member function
templates. I have a shared library containing templates that I'm
trying to use from an executable, compile using gcc 4.1.2. Everything
works fine until I try specializing one of the static member function
templates in a non-template class. I have a feeling I'm messing up
something obvious so before I post a bunch of code does the following
look correct? Thanks.

--- Shared Library (Arrays.h) ---

namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
protected:
Arrays() {};

};

template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
printf("Calling generic function.\n");
return 1;

}

template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
printf("Calling char specialization.\n");
return 0;

}
}- Hide quoted text -

- Show quoted text -
Your specialization should be inside the example:Arrays class, not
outside it.
namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int
length);
static int compareItems(char*a1, char *a2, int
length);
};
You cant add a new specialization once the class declaration is
closed. If compareItems were a namespace level declaration, then you
can reopen the namespace and add a new specialization later.
Lance

Oct 14 '07 #3

P: n/a
mike b wrote:
Hello everyone, thanks in advance for your help. I'm new to C++
templates and have run into some issues using member function
templates. I have a shared library containing templates that I'm
trying to use from an executable, compile using gcc 4.1.2. Everything
works fine until I try specializing one of the static member function
templates in a non-template class. I have a feeling I'm messing up
something obvious so before I post a bunch of code does the following
look correct? Thanks.

--- Shared Library (Arrays.h) ---

namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
protected:
Arrays() {};
};

template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
printf("Calling generic function.\n");
return 1;
}

template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
printf("Calling char specialization.\n");
return 0;
}
}
This below compiles fine and does what I think you expect. What problem
are you having ?

#include <cstdio>
#include <iostream>

namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
Arrays() {};
};

template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
std::printf("Calling generic function.\n");
return 1;
}

template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
std::printf("Calling char specialization.\n");
return 0;
}
}

int main()
{
std::cout << example::Arrays::compareItems( (short*)0, (short*)0, 0
) << "\n";
std::cout << example::Arrays::compareItems( (char*)0, (char*)0, 0 )
<< "\n";
}
Oct 14 '07 #4

P: n/a
On 2007-10-14 20:16, Lance Diduck wrote:
On Oct 14, 12:38 pm, mike b <michaeljber...@gmail.comwrote:
>Hello everyone, thanks in advance for your help. I'm new to C++
templates and have run into some issues using member function
templates. I have a shared library containing templates that I'm
trying to use from an executable, compile using gcc 4.1.2. Everything
works fine until I try specializing one of the static member function
templates in a non-template class. I have a feeling I'm messing up
something obvious so before I post a bunch of code does the following
look correct? Thanks.

--- Shared Library (Arrays.h) ---

namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
protected:
Arrays() {};

};

template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
printf("Calling generic function.\n");
return 1;

}

template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
printf("Calling char specialization.\n");
return 0;

}
}- Hide quoted text -

- Show quoted text -
Your specialization should be inside the example:Arrays class, not
outside it.
namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int
length);
static int compareItems(char*a1, char *a2, int
length);
};
Actually, what you are suggesting is not a specialisation, but declaring
a non-parametrised function taking care of the special case. Which, to
my knowledge, will work just as well but there are probably some subtle
details that make specialised parametrised functions different from
normal functions.

--
Erik Wikström
Oct 14 '07 #5

P: n/a
On Oct 14, 11:16 pm, Lance Diduck <lancedid...@nyc.rr.comwrote:
On Oct 14, 12:38 pm, mike b <michaeljber...@gmail.comwrote:
Your specialization should be inside the example:Arrays class, not
outside it.
namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int
length);
static int compareItems(char*a1, char *a2, int
length);
};
IIRR, a template specialization will always start with the word
"template". Hence, the above (non-template) function is surely not a
specialization of the template function.

>
You cant add a new specialization once the class declaration is
closed.
14.7.3(2) says:
"An explicit specialization of a member function, member class or
static data member of a class template shall be declared in the
namespace of which the class template is a member"

Which means that new specializations can be added in the same
namespace.

-N

Oct 14 '07 #6

P: n/a
On Oct 14, 2:16 pm, Lance Diduck <lancedid...@nyc.rr.comwrote:
On Oct 14, 12:38 pm, mike b <michaeljber...@gmail.comwrote:
Hello everyone, thanks in advance for your help. I'm new to C++
templates and have run into some issues using member function
templates. I have a shared library containing templates that I'm
trying to use from an executable, compile using gcc 4.1.2. Everything
works fine until I try specializing one of the static member function
templates in a non-template class. I have a feeling I'm messing up
something obvious so before I post a bunch of code does the following
look correct? Thanks.
--- Shared Library (Arrays.h) ---
namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
protected:
Arrays() {};
};
template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
printf("Calling generic function.\n");
return 1;
}
template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
printf("Calling char specialization.\n");
return 0;
}
}- Hide quoted text -
- Show quoted text -

Your specialization should be inside the example:Arrays class, not
outside it.
namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int
length);
static int compareItems(char*a1, char *a2, int
length);
};

You cant add a new specialization once the class declaration is
closed. If compareItems were a namespace level declaration, then you
can reopen the namespace and add a new specialization later.
Lance
I tried this but it doesn't automatically call my specialization. Do
I need to call overloaded implementations of the function from inside
the generic implementation? So basically don't use specialization at
all, use overloading from within the single generic implementation?

Oct 14 '07 #7

P: n/a
On Oct 14, 2:16 pm, Gianni Mariani <gi4nos...@marian.wswrote:
mike b wrote:
Hello everyone, thanks in advance for your help. I'm new to C++
templates and have run into some issues using member function
templates. I have a shared library containing templates that I'm
trying to use from an executable, compile using gcc 4.1.2. Everything
works fine until I try specializing one of the static member function
templates in a non-template class. I have a feeling I'm messing up
something obvious so before I post a bunch of code does the following
look correct? Thanks.
--- Shared Library (Arrays.h) ---
namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
protected:
Arrays() {};
};
template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
printf("Calling generic function.\n");
return 1;
}
template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
printf("Calling char specialization.\n");
return 0;
}
}

This below compiles fine and does what I think you expect. What problem
are you having ?

#include <cstdio>
#include <iostream>

namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
Arrays() {};

};

template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
std::printf("Calling generic function.\n");
return 1;

}

template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
std::printf("Calling char specialization.\n");
return 0;

}
}

int main()
{
std::cout << example::Arrays::compareItems( (short*)0, (short*)0, 0
) << "\n";
std::cout << example::Arrays::compareItems( (char*)0, (char*)0, 0 )
<< "\n";

}
The problem only occurs when code is separated into multiple binaries,
a shared lib and executable, with multiple users in the app.

Oct 14 '07 #8

P: n/a
mike b wrote:
On Oct 14, 2:16 pm, Gianni Mariani <gi4nos...@marian.wswrote:
....
The problem only occurs when code is separated into multiple binaries,
a shared lib and executable, with multiple users in the app.

Are definitions of all template functions in every compilation unit ?
(i.e. included into every binary's source in question ?) If not, that's
your problem.
Oct 14 '07 #9

P: n/a
On Oct 14, 6:13 pm, Gianni Mariani <gi4nos...@marian.wswrote:
mike b wrote:
On Oct 14, 2:16 pm, Gianni Mariani <gi4nos...@marian.wswrote:
...
The problem only occurs when code is separated into multiple binaries,
a shared lib and executable, with multiple users in the app.

Are definitions of all template functions in every compilation unit ?
(i.e. included into every binary's source in question ?) If not, that's
your problem.
I defined my entire template class in the header file (.h) so it
should be making it into every compilation unit. Is there something
aside from that I need to do?

Oct 15 '07 #10

P: n/a
On Oct 14, 12:38 pm, mike b <michaeljber...@gmail.comwrote:
Hello everyone, thanks in advance for your help. I'm new to C++
templates and have run into some issues using member function
templates. I have a shared library containing templates that I'm
trying to use from an executable, compile using gcc 4.1.2. Everything
works fine until I try specializing one of the static member function
templates in a non-template class. I have a feeling I'm messing up
something obvious so before I post a bunch of code does the following
look correct? Thanks.

--- Shared Library (Arrays.h) ---

namespace example {
class Arrays {
public:
template<class Tstatic int compareItems(T *a1, T *a2, int length);
protected:
Arrays() {};

};

template<class Tint Arrays::compareItems(T *a1, T *a2, int length) {
printf("Calling generic function.\n");
return 1;

}

template<int Arrays::compareItems<char>(char *a1, char *a2, int
length) {
printf("Calling char specialization.\n");
return 0;

}
}
Sincere thanks to everyone who responded, the problem has been
solved. The issue it seems is that I was defining my member
specializations in the header but only a declaration for the
specialization is allowed in the header, the actual implementation
must go in the implementation file, .cpp. So here is the change to
make the code work:

--- Arrays.h ---

namespace example {
class Arrays : public Object {
public:
template<class Tstatic int compareItems(const T a1[], const
T a2[], const int length);
};

// I was defining the function here but only the declaration goes here
template<int Arrays::compareItems(const char a1[], const char a2[],
const int length);

template<class Tint compareItems(const T a1[], const T a2[], const
int length) {
// Generic implementation goes here.
}
}
--- Arrays.cpp ---

// This was in the header file before and was causing the problems,
moving it here solved it.
template<int hydro::Arrays::compareItems(const char a1[], const char
a2[], const int length) {
return strncmp(a1, a2, length);
}

--- END ---

Oct 15 '07 #11

P: n/a
mike b wrote:
....
Sincere thanks to everyone who responded, the problem has been
solved. The issue it seems is that I was defining my member
specializations in the header but only a declaration for the
specialization is allowed in the header, the actual implementation
must go in the implementation file, .cpp.
Sounds strange. What errors were you getting ?
Oct 16 '07 #12

P: n/a
On Oct 16, 3:45 pm, Gianni Mariani <gi4nos...@marian.wswrote:
mike b wrote:

...
Sincere thanks to everyone who responded, the problem has been
solved. The issue it seems is that I was defining my member
specializations in the header but only a declaration for the
specialization is allowed in the header, the actual implementation
must go in the implementation file, .cpp.

Sounds strange. What errors were you getting ?
I was getting errors about my specialization being defined multiple
times. This was with GCC 4.

Oct 17 '07 #13

P: n/a
mike b wrote:
On Oct 16, 3:45 pm, Gianni Mariani <gi4nos...@marian.wswrote:
>mike b wrote:

...
>>Sincere thanks to everyone who responded, the problem has been
solved. The issue it seems is that I was defining my member
specializations in the header but only a declaration for the
specialization is allowed in the header, the actual implementation
must go in the implementation file, .cpp.
Sounds strange. What errors were you getting ?

I was getting errors about my specialization being defined multiple
times. This was with GCC 4.

Declare the template as "inline" as see if you get the same errors.
Oct 17 '07 #14

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