How do I get the argument types of a function pointer

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I want to get the argument types of a function pointer like this : (second line)

C#

typedef void (*fun)(int);
GetParam1Type<fun>::Result  <----Result为int

is not necessarily to use template,and must support class member function pointer.

Posted 25-Nov-13 0:35am

liuhaopeng

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Philippe Mori 25-Nov-13 19:49pm

If you want to do Advanced Template stuff, then you should read books on that topic like C++ Template Metaprogramming (or maybe something more recent) as the language as evolve a lot since then (C++11)

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Stefan_Lang · Answer 1 · 2013-11-25T01:46:00

As Carlo pointed out, there is no way to retrieve this information at runtime. However, you can inquire and use type information at compile time through the use of templates: the easiest way would be with the C++ 11 extensions decltype or std::result_of, or if you use GCC, it has an extension called typeof. (I'm not familiar with either, and have no compiler installed to write and test code for your purpose though.)

Even without these, it should be possible, but before I start wringing a knot into my brain to come up with a standard template solution, is compile time resolution even sufficient for your purposes?

P.S.: here is a thread on stack overflow about function argument types which may be of help: Function argument type[^]

CPallini · Answer 2 · 2013-11-25T00:45:00

Solution 1

Simply stated, you cannot. C++ programming language provides no reflection facilities. However you might implement your own mechanism (for instance, MS did it with IDispatch).

Posted 25-Nov-13 0:45am

CPallini

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Philippe Mori 25-Nov-13 19:45pm

Using templates, you can get a lot of informations from types...

liuhaopeng · Answer 3 · 2013-11-26T03:48:00

C++

#include <iostream>
#include <type_traits>
 
struct A{};
  
template< typename T/*, typename U */>
struct GetParam1Type;
  
template< typename T, typename U, typename V >
struct GetParam1Type< T( U, V ) >
{
    typedef U Result;
};
 
template< typename T, typename U, typename V , typename R>
struct GetParam1Type< T( U, V ,R) >
{
    typedef U Result;
};
  
template< typename T >
struct GetParam1Type< T( void ) >
{
    typedef void Result;
};
  
template< typename T, typename U, typename V >
struct GetParam1Type< T( * )( U, V) >
{
    typedef U Result;
};
 
template< typename T, typename U, typename V , typename R>
struct GetParam1Type< T( * )( U, V ,R) >
{
    typedef U Result;
};
  
template< typename T >
struct GetParam1Type< T( * )( void ) >
{
    typedef void Result;
};
  
template< typename T, typename U, typename V, typename R >
struct GetParam1Type< T ( V::* )( U, R ) >
{
    typedef U Result;
};
 
template< typename T, typename U, typename V, typename R , typename A>
struct GetParam1Type< T ( V::* )( U, R ,A) >
{
    typedef U Result;
};
  
template< typename T, typename V >
struct GetParam1Type< T ( V::* )( void ) >
{
    typedef void Result;
};
  
typedef void ( A::*fun1 )( int, long, double );
typedef void ( A::*fun2 )(  );
typedef long fun3( int, long, double );
typedef long fun4(  );
typedef long ( *fun5 )( int, long, double );
typedef long ( *fun6 )(  );
 
int main( void )
{
    std::cout << std::is_same< GetParam1Type< fun1 >::Result, int >::value << std::endl;
    std::cout << std::is_same< GetParam1Type< fun2 >::Result, void >::value << std::endl;
    std::cout << std::is_same< GetParam1Type< fun3 >::Result, int >::value << std::endl;
    std::cout << std::is_same< GetParam1Type< fun4 >::Result, void >::value << std::endl;
    std::cout << std::is_same< GetParam1Type< fun5 >::Result, int >::value << std::endl;
    std::cout << std::is_same< GetParam1Type< fun6 >::Result, void >::value << std::endl;
    getchar();
    return 0;
}

How do I get the argument types of a function pointer

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