Question on arrays of pointers to functions in C++

[C. J. Clegg]

Consider the following code...

class MyClass
{
public:
int Fct1( void );
int Fct2( void );
int Fct3( void );

void ExecFcts( void );
};

int MyClass::fct1( void )
{
// do some stuff
return 0
}

int MyClass::fct2( void )
{
// do some different stuff
return 0
}

int MyClass::fct3( void )
{
// do some still different stuff
return 0
}

void MyClass::ExecFcts( void )
{
struct
{
int anIntVar;
int (MyClass::*TheFct)( void );
} arrayOfFcts[ ] =
{
{ 0, &MyClass::Fct1 },
{ 1, &MyClass::Fct2 },
{ 2, &MyClass::Fct3 }
};

// This all compiles OK up to here.
// Then...
//
// try to call one of the functions in the struct array

arrayOfFcts[ 0 ].TheFct( );
// This makes a compile error
}

int main( int argc, char** argv )
{
MyClass theClass;

theClass.ExecFcts();

return 0;
}

I have read through the FAQ and every post I can find on dejanews on
this topic, in fact the FAQ educated me on the difference between a
pointer to a member function and a pointer to a non-member function
and the need to prepend "MyClass::" to the function names in the
struct array, and allowed me to get a clean compile up to the point
indicated in the code comment above.

But, I can't get the correct syntax for the function call.

I have tried every combination I can think of of:

arrayOfFcts[ 0 ].MyClass::TheFct( );
arrayOfFcts[ 0 ].*MyClass::TheFct( );
arrayOfFcts[ 0 ].MyClass::*TheFct( );

( ... with and without parens sprinkled liberally about...)

....and no luck.

I have done my research ... honest ... and I'm out of ideas.

 

[Victor Bazarov]

[...]
// try to call one of the functions in the struct array

arrayOfFcts[ 0 ].TheFct( );

Should be

(this->*(arrayOfFcts[0].TheFct))();

// This makes a compile error
}
[...]

And next time please don't type your code directly into the posting,
you made several typos.

V

 

[Jakob Bieling]

Consider the following code...

class MyClass
{
public:
int Fct1( void );
int Fct2( void );
int Fct3( void );

void ExecFcts( void );
};

int MyClass::fct1( void )
{
// do some stuff
return 0
}

int MyClass::fct2( void )
{
// do some different stuff
return 0
}

int MyClass::fct3( void )
{
// do some still different stuff
return 0
}

void MyClass::ExecFcts( void )
{
struct
{
int anIntVar;
int (MyClass::*TheFct)( void );
} arrayOfFcts[ ] =
{
{ 0, &MyClass::Fct1 },
{ 1, &MyClass::Fct2 },
{ 2, &MyClass::Fct3 }
};

// This all compiles OK up to here.
// Then...
//
// try to call one of the functions in the struct array

arrayOfFcts[ 0 ].TheFct( );
// This makes a compile error
}

int main( int argc, char** argv )
{
MyClass theClass;

theClass.ExecFcts();

return 0;
}

I have read through the FAQ and every post I can find on dejanews on
this topic, in fact the FAQ educated me on the difference between a
pointer to a member function and a pointer to a non-member function
and the need to prepend "MyClass::" to the function names in the
struct array, and allowed me to get a clean compile up to the point
indicated in the code comment above.

But, I can't get the correct syntax for the function call.

I have tried every combination I can think of of:

arrayOfFcts[ 0 ].MyClass::TheFct( );
arrayOfFcts[ 0 ].*MyClass::TheFct( );
arrayOfFcts[ 0 ].MyClass::*TheFct( );

Almost. I suppose you know that member functions need an object to
work with, considering you did the research In your code, you do not
provide any object, though. This is why this won't work. Try this
instead:

(this->*arrayOfFcts[0].TheFct) ();

For a 'regular' call (at the same code location!, ie. inside a
member function), as in 'Fct1 ();', you do not need to explicitly
provide an object, because 'this' is used implicitly. When you use
pointers, you must provide the object explicitly .. even inside a member
function.

hth

 

[C. J. Clegg]

Should be

(this->*(arrayOfFcts[0].TheFct))();

Good afternoon, Victor and Jakob.

Thanks to both of you for that... it's the one variation I didn't try
(naturally), and it worked fine.

And next time please don't type your code directly into the posting,

Hmmm ... Really? OK, I can refrain from doing that in the future, but
how do I provide code samples that illustrate the problem?

Thanks again...

 

[Jakob Bieling]

how do I provide code samples that illustrate the problem?

You should compile the code until the only errors (if any) left are
the ones you are having problems with.

regards

 

[Victor Bazarov]

On Mon, 10 Apr 2006 11:55:38 -0400, "Victor Bazarov"


Hmmm ... Really? OK, I can refrain from doing that in the future, but
how do I provide code samples that illustrate the problem?

Copy and paste. I am betting your text editor and news reader allow you
to do so.

 

[C. J. Clegg]

You should compile the code until the only errors (if any) left are
the ones you are having problems with.

Ah, OK, understood.

I actually did that, sort of ... the code I put in my posting (I guess
nobody calls these postings "articles" anymore) was a vastly
oversimplified version of some code that is in an application I'm
writing, and I figured you guys wouldn't want to wade through all the
baggage that comes with the real thing, so I simplified it to the
simplest possible form and used that. I did compile the actual code
but didn't compile my simplified sample first ... sorry.

 

[C. J. Clegg]

Copy and paste. I am betting your text editor and news reader allow you
to do so.

Ah, OK, I misunderstood what you said, thought you meant not to put
the code in the posting at all.

Got it.