pointers to templated c++ functions

gearoid_murphy · 08-11-2006, 08:34 AM

does anyone know how to create a typedef'd pointer to a function in c++ ?, I'm stumped.

exman · 08-11-2006, 08:45 AM

Hi,
some sample code that worked for me:

Code:

#include <iostream>
using namespace std;

int foo(int a, int b)
{
        return a+b;
}

typedef int(*add_t)(int,int);


void bar(add_t func)
{
        cout<<func(1,1)<<endl;
}

int main()
{
        bar(foo);
        return 0;
}

exman

dmail · 08-11-2006, 09:13 AM

Code:

int main()
{
        bar(foo);
        return 0;
}

The above is correct C code but not good C++ code, C++ should include the ampersand operator.

Code:

int main()
{
        bar(&foo);
        return 0;
}

exman · 08-11-2006, 09:24 AM

Hi,

tried that and works too.
But both dont bring up a warning with

Code:

g++ -o td -Wall td.cpp -pedantic

Could you explain why one should use the &?
Im just interested.

exman

xhi · 08-11-2006, 09:37 AM

hmm

i thought & was optional in both, same meaning with or without

dmail · 08-11-2006, 09:52 AM

Quote:

Originally Posted by xhi

hmm

i thought & was optional in both, same meaning with or without

This is why I didn't say "none valid" or "bad" rather just "not good"
The ampersand is required for none static member functions and it's just good style to be consistant.
Sorry if I mislead you.

gearoid_murphy · 08-11-2006, 10:06 AM

yeah, shit, I forgot to mention that the functions were templated, kindof a big detail to forget. Anyways I now think that it isn't possible as I should be able to create pointers to instansiated functions but not to abstract templates of functions, could someone confirm or deny the please?, much obliged Gearoid

dmail · 08-11-2006, 10:35 AM

Can you give a small example to what you mean(member functions?), code speaks a thousand words

I'm also trying to think of a need for this?

xhi · 08-11-2006, 11:00 AM

Quote:

Originally Posted by dmail

This is why I didn't say "none valid" or "bad" rather just "not good"
The ampersand is required for none static member functions and it's just good style to be consistant.
Sorry if I mislead you.

yeh true. i think ive been coding in c for too long lately.

orhun · 08-11-2006, 12:08 PM

I don't have access to gcc right now but this worked for me under VC80.

Code:

template<typename T>
void MyTemplatedFunction(const T& t)
{
	std::cout << t << std::endl;
}


typedef void (*FuncIntT)(const int&);
typedef void (*FuncStrT)(const std::string&);

int main(int argc, char* argv[])
{
	FuncIntT func1(&MyTemplatedFunction);
	func1(5);

	FuncStrT func2(&MyTemplatedFunction);
	func2("string");
	return 0;
}

exman · 08-11-2006, 12:22 PM

Quote:

Originally Posted by gearoid_murphy

yeah,could someone confirm or deny the please?

I tried orhun's example with something like this

Code:

template<typename T>
typedef T (*foo)(T&,T&);

g++ -o tpp test.cpp
test.cpp:11: error: templatedeclaration of »typedef«
So its not possible or at least not that easy

exman

xhi · 08-11-2006, 01:12 PM

could you give an example of what you are trying to accomplish? what purpose will these function pointers serve?