Re: function pointers

From:

John Moeller <fishcorn@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 19 Jun 2007 23:48:53 CST

Message-ID:

<f59tbt$8ks$1@news.xmission.com>

ender wrote:

why can't the new operator be used on function pointers?

Can you post an example of what you are trying to do?

maybe I have the syntax wrong but when I tried creating a vector of
the form vector< int (*)(window, unsigned int)> I got a compile time
error stating that new could not be used on int (*)(window, unsigned
int). perhaps I am just ignorent of the correct way to pass a
function pointer type as a template argument (or use it in a
typedef). If that is the cause could you tell me the correct syntax?

I had no trouble with the following program on MSVC++ 2005 EE:

   #include <vector>

   struct window {};

   int fn(window, unsigned int) { return 0; }

   int main(int, char * [])
   {
     std::vector< int (*)(window, unsigned int)> v(5);

     v[2] = fn;

     return (*(v[2]))(window(), 0);
   }

One trick that I often use if I can't get certain things to compile is
to use typedefs. Especially in the case of function pointers, it can
make things easier to understand:

typedef int (*fn_ptr)(window, unsigned int);
std::vector<fn_ptr> v(5);

This would be equivalent to the single-line declaration in the above
program.

--

John Moeller
fishcorn@gmail.com

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