Q: Map of pointers to member functions

[Jim]

I'd like to create a map of strings to member function pointers, so that I
can call a specific function based on a string. I'm compiling this using MS
Visual C++ 7.0 (VS.NET 2002)

class Foo;

/// Prototype for functions that extract a parameter from a module
typedef const void (Foo::*PARAM_GETTER)(std::string&);

/// A map of strings to parameter getters
typedef std::map<std::string, PARAM_GETTER> ParamGetterMap;

And then,

class Foo
{
protected:
ParamGetterMap m_getterMap;
};

class Bar : public AnotherBaseClass, public Foo
{
private:
// getter/setter helpers
void GetBar(std::string& strValue) { strValue = "something"; }
};

And finally,

Bar::Bar()
{
// Fill the parameter maps
m_getterMap.insert(make_pair("bar", GetBar)); // COMPLILE ERROR HERE
}

I get the following compile error:

C:\Microsoft Visual Studio .NET\Vc7\include\utility(41) : error C2440:
'initializing' : cannot
convert from 'void (__thiscall Bar::* const )(std::string &)' to
'PARAM_GETTER '
Types pointed to are unrelated; conversion requires reinterpret_cast,
C-style cast or
function-style cast
Bar.cpp(41) : see
reference to function template instantiation 'std:air<_Ty1,_Ty2>:air
(const std:air<char,void
(__thiscall Bar::* )(std::string &)> &)' being compiled
with
[
_Ty1=const std::string,
_Ty2=PARAM_GETTER
]
C:\Microsoft Visual Studio .NET\Vc7\include\utility(41) : error C2439:
'std:air<_Ty1,_Ty2>::second' : member could not be initialized
with
[
_Ty1=const std::string,
_Ty2=PARAM_GETTER
]
C:\Microsoft Visual Studio .NET\Vc7\include\utility(56) : see
declaration of
'std:air<_Ty1,_Ty2>::second'
with
[
_Ty1=const std::string,
_Ty2=PARAM_GETTER
]

Can anyone point out what I'm doing wrong here?

Thx x 10^6

 

[Michael Etscheid]

m_getterMap.insert(make_pair("bar", GetBar)); // COMPLILE ERROR HERE

GetBar is only defined in Bar but PARAM_GETTER is a function pointer to
a member function of Foo:

typedef const void (Foo::*PARAM_GETTER)(std::string&);

I hope that helps you.

 

[Jim]

GetBar is only defined in Bar but PARAM_GETTER is a function pointer to
a member function of Foo:


I hope that helps you.

A little; but it doesn't point to a solution.

I've used a similar technique before and it worked; I had to cast the
function pointer to a specific type to clear up a different error, however
here I can't get even that close (the cast gives me severe warning).

 

[Victor Bazarov]

[...]
Bar::Bar()
{
// Fill the parameter maps
m_getterMap.insert(make_pair("bar", GetBar)); // COMPLILE ERROR HERE

The address of a non-static member function cannot be obtained by using
only its name. The format is &Bar::GetBar. It is required.

 

[Jim]

[...]
Bar::Bar()
{
// Fill the parameter maps
m_getterMap.insert(make_pair("bar", GetBar)); // COMPLILE ERROR HERE

The address of a non-static member function cannot be obtained by using
only its name. The format is &Bar::GetBar. It is required.

}

Thanks; but using the syntax you specified makes no difference (same compile
error).

 

[red floyd]

A little; but it doesn't point to a solution.

I've used a similar technique before and it worked; I had to cast the
function pointer to a specific type to clear up a different error, however
here I can't get even that close (the cast gives me severe warning).

No, what he's saying is your map translates from std::string to Foo::*
member.
You're trying to pass it a Bar::* member. The typedef in the error
message is hiding it. Look at the def of PARAM_GETTER, and the def of
GetBar().

 

[Victor Bazarov]

[...]
Bar::Bar()
{
// Fill the parameter maps
m_getterMap.insert(make_pair("bar", GetBar)); // COMPLILE ERROR HERE

The address of a non-static member function cannot be obtained by using
only its name. The format is &Bar::GetBar. It is required.

}

Thanks; but using the syntax you specified makes no difference (same compile
error).

Sorry, solved a wrong problem

A pointer to member of a derived class is not convertible to a pointer
to member of the base class. It does work that way for pointers to
objects, but works _in_reverse_ for pointers to members.

To convert a pointer to member you need a static_cast.
--------------------------------------------------------
Bar::Bar()
{
// Fill the parameter maps
m_getterMap.insert(std::make_pair("bar",
static_cast<PARAM_GETTER>(&Bar::GetBar))); // NO ERROR HERE
}